doctest.rst 67 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
:mod:`doctest` --- Test interactive Python examples
===================================================

.. module:: doctest
   :synopsis: Test pieces of code within docstrings.
.. moduleauthor:: Tim Peters <tim@python.org>
.. sectionauthor:: Tim Peters <tim@python.org>
.. sectionauthor:: Moshe Zadka <moshez@debian.org>
.. sectionauthor:: Edward Loper <edloper@users.sourceforge.net>


The :mod:`doctest` module searches for pieces of text that look like interactive
Python sessions, and then executes those sessions to verify that they work
exactly as shown.  There are several common ways to use doctest:

* To check that a module's docstrings are up-to-date by verifying that all
  interactive examples still work as documented.

* To perform regression testing by verifying that interactive examples from a
  test file or a test object work as expected.

* To write tutorial documentation for a package, liberally illustrated with
  input-output examples.  Depending on whether the examples or the expository text
  are emphasized, this has the flavor of "literate testing" or "executable
  documentation".

Here's a complete but small example module::

   """
   This is the "example" module.

   The example module supplies one function, factorial().  For example,

   >>> factorial(5)
   120
   """

   def factorial(n):
       """Return the factorial of n, an exact integer >= 0.

       >>> [factorial(n) for n in range(6)]
       [1, 1, 2, 6, 24, 120]
       >>> factorial(30)
44
       265252859812191058636308480000000
45 46 47 48 49 50 51 52 53 54 55
       >>> factorial(-1)
       Traceback (most recent call last):
           ...
       ValueError: n must be >= 0

       Factorials of floats are OK, but the float must be an exact integer:
       >>> factorial(30.1)
       Traceback (most recent call last):
           ...
       ValueError: n must be exact integer
       >>> factorial(30.0)
56
       265252859812191058636308480000000
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

       It must also not be ridiculously large:
       >>> factorial(1e100)
       Traceback (most recent call last):
           ...
       OverflowError: n too large
       """

       import math
       if not n >= 0:
           raise ValueError("n must be >= 0")
       if math.floor(n) != n:
           raise ValueError("n must be exact integer")
       if n+1 == n:  # catch a value like 1e300
           raise OverflowError("n too large")
       result = 1
       factor = 2
       while factor <= n:
           result *= factor
           factor += 1
       return result


   if __name__ == "__main__":
81 82
       import doctest
       doctest.testmod()
83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117

If you run :file:`example.py` directly from the command line, :mod:`doctest`
works its magic::

   $ python example.py
   $

There's no output!  That's normal, and it means all the examples worked.  Pass
:option:`-v` to the script, and :mod:`doctest` prints a detailed log of what
it's trying, and prints a summary at the end::

   $ python example.py -v
   Trying:
       factorial(5)
   Expecting:
       120
   ok
   Trying:
       [factorial(n) for n in range(6)]
   Expecting:
       [1, 1, 2, 6, 24, 120]
   ok

And so on, eventually ending with::

   Trying:
       factorial(1e100)
   Expecting:
       Traceback (most recent call last):
           ...
       OverflowError: n too large
   ok
   2 items passed all tests:
      1 tests in __main__
      8 tests in __main__.factorial
118
   9 tests in 2 items.
119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137
   9 passed and 0 failed.
   Test passed.
   $

That's all you need to know to start making productive use of :mod:`doctest`!
Jump in.  The following sections provide full details.  Note that there are many
examples of doctests in the standard Python test suite and libraries.
Especially useful examples can be found in the standard test file
:file:`Lib/test/test_doctest.py`.


.. _doctest-simple-testmod:

Simple Usage: Checking Examples in Docstrings
---------------------------------------------

The simplest way to start using doctest (but not necessarily the way you'll
continue to do it) is to end each module :mod:`M` with::

138
   if __name__ == "__main__":
139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299
       import doctest
       doctest.testmod()

:mod:`doctest` then examines docstrings in module :mod:`M`.

Running the module as a script causes the examples in the docstrings to get
executed and verified::

   python M.py

This won't display anything unless an example fails, in which case the failing
example(s) and the cause(s) of the failure(s) are printed to stdout, and the
final line of output is ``***Test Failed*** N failures.``, where *N* is the
number of examples that failed.

Run it with the :option:`-v` switch instead::

   python M.py -v

and a detailed report of all examples tried is printed to standard output, along
with assorted summaries at the end.

You can force verbose mode by passing ``verbose=True`` to :func:`testmod`, or
prohibit it by passing ``verbose=False``.  In either of those cases,
``sys.argv`` is not examined by :func:`testmod` (so passing :option:`-v` or not
has no effect).

Since Python 2.6, there is also a command line shortcut for running
:func:`testmod`.  You can instruct the Python interpreter to run the doctest
module directly from the standard library and pass the module name(s) on the
command line::

   python -m doctest -v example.py

This will import :file:`example.py` as a standalone module and run
:func:`testmod` on it.  Note that this may not work correctly if the file is
part of a package and imports other submodules from that package.

For more information on :func:`testmod`, see section :ref:`doctest-basic-api`.


.. _doctest-simple-testfile:

Simple Usage: Checking Examples in a Text File
----------------------------------------------

Another simple application of doctest is testing interactive examples in a text
file.  This can be done with the :func:`testfile` function::

   import doctest
   doctest.testfile("example.txt")

That short script executes and verifies any interactive Python examples
contained in the file :file:`example.txt`.  The file content is treated as if it
were a single giant docstring; the file doesn't need to contain a Python
program!   For example, perhaps :file:`example.txt` contains this::

   The ``example`` module
   ======================

   Using ``factorial``
   -------------------

   This is an example text file in reStructuredText format.  First import
   ``factorial`` from the ``example`` module:

       >>> from example import factorial

   Now use it:

       >>> factorial(6)
       120

Running ``doctest.testfile("example.txt")`` then finds the error in this
documentation::

   File "./example.txt", line 14, in example.txt
   Failed example:
       factorial(6)
   Expected:
       120
   Got:
       720

As with :func:`testmod`, :func:`testfile` won't display anything unless an
example fails.  If an example does fail, then the failing example(s) and the
cause(s) of the failure(s) are printed to stdout, using the same format as
:func:`testmod`.

By default, :func:`testfile` looks for files in the calling module's directory.
See section :ref:`doctest-basic-api` for a description of the optional arguments
that can be used to tell it to look for files in other locations.

Like :func:`testmod`, :func:`testfile`'s verbosity can be set with the
:option:`-v` command-line switch or with the optional keyword argument
*verbose*.

Since Python 2.6, there is also a command line shortcut for running
:func:`testfile`.  You can instruct the Python interpreter to run the doctest
module directly from the standard library and pass the file name(s) on the
command line::

   python -m doctest -v example.txt

Because the file name does not end with :file:`.py`, :mod:`doctest` infers that
it must be run with :func:`testfile`, not :func:`testmod`.

For more information on :func:`testfile`, see section :ref:`doctest-basic-api`.


.. _doctest-how-it-works:

How It Works
------------

This section examines in detail how doctest works: which docstrings it looks at,
how it finds interactive examples, what execution context it uses, how it
handles exceptions, and how option flags can be used to control its behavior.
This is the information that you need to know to write doctest examples; for
information about actually running doctest on these examples, see the following
sections.


.. _doctest-which-docstrings:

Which Docstrings Are Examined?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The module docstring, and all function, class and method docstrings are
searched.  Objects imported into the module are not searched.

In addition, if ``M.__test__`` exists and "is true", it must be a dict, and each
entry maps a (string) name to a function object, class object, or string.
Function and class object docstrings found from ``M.__test__`` are searched, and
strings are treated as if they were docstrings.  In output, a key ``K`` in
``M.__test__`` appears with name ::

   <name of M>.__test__.K

Any classes found are recursively searched similarly, to test docstrings in
their contained methods and nested classes.


.. _doctest-finding-examples:

How are Docstring Examples Recognized?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In most cases a copy-and-paste of an interactive console session works fine, but
doctest isn't trying to do an exact emulation of any specific Python shell.  All
hard tab characters are expanded to spaces, using 8-column tab stops.  If you
don't believe tabs should mean that, too bad:  don't use hard tabs, or write
your own :class:`DocTestParser` class.

::

   >>> # comments are ignored
   >>> x = 12
   >>> x
   12
   >>> if x == 13:
300
   ...     print("yes")
301
   ... else:
302 303 304
   ...     print("no")
   ...     print("NO")
   ...     print("NO!!!")
305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330
   ...
   no
   NO
   NO!!!
   >>>

Any expected output must immediately follow the final ``'>>> '`` or ``'... '``
line containing the code, and the expected output (if any) extends to the next
``'>>> '`` or all-whitespace line.

The fine print:

* Expected output cannot contain an all-whitespace line, since such a line is
  taken to signal the end of expected output.  If expected output does contain a
  blank line, put ``<BLANKLINE>`` in your doctest example each place a blank line
  is expected.

* Output to stdout is captured, but not output to stderr (exception tracebacks
  are captured via a different means).

* If you continue a line via backslashing in an interactive session, or for any
  other reason use a backslash, you should use a raw docstring, which will
  preserve your backslashes exactly as you type them::

     >>> def f(x):
     ...     r'''Backslashes in a raw docstring: m\n'''
331
     >>> print(f.__doc__)
332 333 334 335 336 337 338 339
     Backslashes in a raw docstring: m\n

  Otherwise, the backslash will be interpreted as part of the string. For example,
  the "\\" above would be interpreted as a newline character.  Alternatively, you
  can double each backslash in the doctest version (and not use a raw string)::

     >>> def f(x):
     ...     '''Backslashes in a raw docstring: m\\n'''
340
     >>> print(f.__doc__)
341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629
     Backslashes in a raw docstring: m\n

* The starting column doesn't matter::

     >>> assert "Easy!"
           >>> import math
               >>> math.floor(1.9)
               1.0

  and as many leading whitespace characters are stripped from the expected output
  as appeared in the initial ``'>>> '`` line that started the example.


.. _doctest-execution-context:

What's the Execution Context?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

By default, each time :mod:`doctest` finds a docstring to test, it uses a
*shallow copy* of :mod:`M`'s globals, so that running tests doesn't change the
module's real globals, and so that one test in :mod:`M` can't leave behind
crumbs that accidentally allow another test to work.  This means examples can
freely use any names defined at top-level in :mod:`M`, and names defined earlier
in the docstring being run. Examples cannot see names defined in other
docstrings.

You can force use of your own dict as the execution context by passing
``globs=your_dict`` to :func:`testmod` or :func:`testfile` instead.


.. _doctest-exceptions:

What About Exceptions?
^^^^^^^^^^^^^^^^^^^^^^

No problem, provided that the traceback is the only output produced by the
example:  just paste in the traceback. [#]_ Since tracebacks contain details
that are likely to change rapidly (for example, exact file paths and line
numbers), this is one case where doctest works hard to be flexible in what it
accepts.

Simple example::

   >>> [1, 2, 3].remove(42)
   Traceback (most recent call last):
     File "<stdin>", line 1, in ?
   ValueError: list.remove(x): x not in list

That doctest succeeds if :exc:`ValueError` is raised, with the ``list.remove(x):
x not in list`` detail as shown.

The expected output for an exception must start with a traceback header, which
may be either of the following two lines, indented the same as the first line of
the example::

   Traceback (most recent call last):
   Traceback (innermost last):

The traceback header is followed by an optional traceback stack, whose contents
are ignored by doctest.  The traceback stack is typically omitted, or copied
verbatim from an interactive session.

The traceback stack is followed by the most interesting part: the line(s)
containing the exception type and detail.  This is usually the last line of a
traceback, but can extend across multiple lines if the exception has a
multi-line detail::

   >>> raise ValueError('multi\n    line\ndetail')
   Traceback (most recent call last):
     File "<stdin>", line 1, in ?
   ValueError: multi
       line
   detail

The last three lines (starting with :exc:`ValueError`) are compared against the
exception's type and detail, and the rest are ignored.

Best practice is to omit the traceback stack, unless it adds significant
documentation value to the example.  So the last example is probably better as::

   >>> raise ValueError('multi\n    line\ndetail')
   Traceback (most recent call last):
       ...
   ValueError: multi
       line
   detail

Note that tracebacks are treated very specially.  In particular, in the
rewritten example, the use of ``...`` is independent of doctest's
:const:`ELLIPSIS` option.  The ellipsis in that example could be left out, or
could just as well be three (or three hundred) commas or digits, or an indented
transcript of a Monty Python skit.

Some details you should read once, but won't need to remember:

* Doctest can't guess whether your expected output came from an exception
  traceback or from ordinary printing.  So, e.g., an example that expects
  ``ValueError: 42 is prime`` will pass whether :exc:`ValueError` is actually
  raised or if the example merely prints that traceback text.  In practice,
  ordinary output rarely begins with a traceback header line, so this doesn't
  create real problems.

* Each line of the traceback stack (if present) must be indented further than
  the first line of the example, *or* start with a non-alphanumeric character.
  The first line following the traceback header indented the same and starting
  with an alphanumeric is taken to be the start of the exception detail.  Of
  course this does the right thing for genuine tracebacks.

* When the :const:`IGNORE_EXCEPTION_DETAIL` doctest option is is specified,
  everything following the leftmost colon is ignored.

* The interactive shell omits the traceback header line for some
  :exc:`SyntaxError`\ s.  But doctest uses the traceback header line to
  distinguish exceptions from non-exceptions.  So in the rare case where you need
  to test a :exc:`SyntaxError` that omits the traceback header, you will need to
  manually add the traceback header line to your test example.

* For some :exc:`SyntaxError`\ s, Python displays the character position of the
  syntax error, using a ``^`` marker::

     >>> 1 1
       File "<stdin>", line 1
         1 1
           ^
     SyntaxError: invalid syntax

  Since the lines showing the position of the error come before the exception type
  and detail, they are not checked by doctest.  For example, the following test
  would pass, even though it puts the ``^`` marker in the wrong location::

     >>> 1 1
     Traceback (most recent call last):
       File "<stdin>", line 1
         1 1
         ^
     SyntaxError: invalid syntax


.. _doctest-options:

Option Flags and Directives
^^^^^^^^^^^^^^^^^^^^^^^^^^^

A number of option flags control various aspects of doctest's behavior.
Symbolic names for the flags are supplied as module constants, which can be
or'ed together and passed to various functions.  The names can also be used in
doctest directives (see below).

The first group of options define test semantics, controlling aspects of how
doctest decides whether actual output matches an example's expected output:


.. data:: DONT_ACCEPT_TRUE_FOR_1

   By default, if an expected output block contains just ``1``, an actual output
   block containing just ``1`` or just ``True`` is considered to be a match, and
   similarly for ``0`` versus ``False``.  When :const:`DONT_ACCEPT_TRUE_FOR_1` is
   specified, neither substitution is allowed.  The default behavior caters to that
   Python changed the return type of many functions from integer to boolean;
   doctests expecting "little integer" output still work in these cases.  This
   option will probably go away, but not for several years.


.. data:: DONT_ACCEPT_BLANKLINE

   By default, if an expected output block contains a line containing only the
   string ``<BLANKLINE>``, then that line will match a blank line in the actual
   output.  Because a genuinely blank line delimits the expected output, this is
   the only way to communicate that a blank line is expected.  When
   :const:`DONT_ACCEPT_BLANKLINE` is specified, this substitution is not allowed.


.. data:: NORMALIZE_WHITESPACE

   When specified, all sequences of whitespace (blanks and newlines) are treated as
   equal.  Any sequence of whitespace within the expected output will match any
   sequence of whitespace within the actual output. By default, whitespace must
   match exactly. :const:`NORMALIZE_WHITESPACE` is especially useful when a line of
   expected output is very long, and you want to wrap it across multiple lines in
   your source.


.. data:: ELLIPSIS

   When specified, an ellipsis marker (``...``) in the expected output can match
   any substring in the actual output.  This includes substrings that span line
   boundaries, and empty substrings, so it's best to keep usage of this simple.
   Complicated uses can lead to the same kinds of "oops, it matched too much!"
   surprises that ``.*`` is prone to in regular expressions.


.. data:: IGNORE_EXCEPTION_DETAIL

   When specified, an example that expects an exception passes if an exception of
   the expected type is raised, even if the exception detail does not match.  For
   example, an example expecting ``ValueError: 42`` will pass if the actual
   exception raised is ``ValueError: 3*14``, but will fail, e.g., if
   :exc:`TypeError` is raised.

   Note that a similar effect can be obtained using :const:`ELLIPSIS`, and
   :const:`IGNORE_EXCEPTION_DETAIL` may go away when Python releases prior to 2.4
   become uninteresting.  Until then, :const:`IGNORE_EXCEPTION_DETAIL` is the only
   clear way to write a doctest that doesn't care about the exception detail yet
   continues to pass under Python releases prior to 2.4 (doctest directives appear
   to be comments to them).  For example, ::

      >>> (1, 2)[3] = 'moo' #doctest: +IGNORE_EXCEPTION_DETAIL
      Traceback (most recent call last):
        File "<stdin>", line 1, in ?
      TypeError: object doesn't support item assignment

   passes under Python 2.4 and Python 2.3.  The detail changed in 2.4, to say "does
   not" instead of "doesn't".


.. data:: SKIP

   When specified, do not run the example at all.  This can be useful in contexts
   where doctest examples serve as both documentation and test cases, and an
   example should be included for documentation purposes, but should not be
   checked.  E.g., the example's output might be random; or the example might
   depend on resources which would be unavailable to the test driver.

   The SKIP flag can also be used for temporarily "commenting out" examples.


.. data:: COMPARISON_FLAGS

   A bitmask or'ing together all the comparison flags above.

The second group of options controls how test failures are reported:


.. data:: REPORT_UDIFF

   When specified, failures that involve multi-line expected and actual outputs are
   displayed using a unified diff.


.. data:: REPORT_CDIFF

   When specified, failures that involve multi-line expected and actual outputs
   will be displayed using a context diff.


.. data:: REPORT_NDIFF

   When specified, differences are computed by ``difflib.Differ``, using the same
   algorithm as the popular :file:`ndiff.py` utility. This is the only method that
   marks differences within lines as well as across lines.  For example, if a line
   of expected output contains digit ``1`` where actual output contains letter
   ``l``, a line is inserted with a caret marking the mismatching column positions.


.. data:: REPORT_ONLY_FIRST_FAILURE

   When specified, display the first failing example in each doctest, but suppress
   output for all remaining examples.  This will prevent doctest from reporting
   correct examples that break because of earlier failures; but it might also hide
   incorrect examples that fail independently of the first failure.  When
   :const:`REPORT_ONLY_FIRST_FAILURE` is specified, the remaining examples are
   still run, and still count towards the total number of failures reported; only
   the output is suppressed.


.. data:: REPORTING_FLAGS

   A bitmask or'ing together all the reporting flags above.

"Doctest directives" may be used to modify the option flags for individual
examples.  Doctest directives are expressed as a special Python comment
following an example's source code:

.. productionlist:: doctest
   directive: "#" "doctest:" `directive_options`
   directive_options: `directive_option` ("," `directive_option`)\*
   directive_option: `on_or_off` `directive_option_name`
   on_or_off: "+" \| "-"
   directive_option_name: "DONT_ACCEPT_BLANKLINE" \| "NORMALIZE_WHITESPACE" \| ...

Whitespace is not allowed between the ``+`` or ``-`` and the directive option
name.  The directive option name can be any of the option flag names explained
above.

An example's doctest directives modify doctest's behavior for that single
example.  Use ``+`` to enable the named behavior, or ``-`` to disable it.

For example, this test passes::

630
   >>> print(range(20)) #doctest: +NORMALIZE_WHITESPACE
631 632 633 634 635 636 637 638
   [0,   1,  2,  3,  4,  5,  6,  7,  8,  9,
   10,  11, 12, 13, 14, 15, 16, 17, 18, 19]

Without the directive it would fail, both because the actual output doesn't have
two blanks before the single-digit list elements, and because the actual output
is on a single line.  This test also passes, and also requires a directive to do
so::

639
   >>> print(range(20)) # doctest: +ELLIPSIS
640 641 642 643
   [0, 1, ..., 18, 19]

Multiple directives can be used on a single physical line, separated by commas::

644
   >>> print(range(20)) # doctest: +ELLIPSIS, +NORMALIZE_WHITESPACE
645 646 647 648 649
   [0,    1, ...,   18,    19]

If multiple directive comments are used for a single example, then they are
combined::

650
   >>> print(range(20)) # doctest: +ELLIPSIS
651 652 653 654 655 656 657
   ...                 # doctest: +NORMALIZE_WHITESPACE
   [0,    1, ...,   18,    19]

As the previous example shows, you can add ``...`` lines to your example
containing only directives.  This can be useful when an example is too long for
a directive to comfortably fit on the same line::

658
   >>> print(range(5) + range(10,20) + range(30,40) + range(50,60))
659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736
   ... # doctest: +ELLIPSIS
   [0, ..., 4, 10, ..., 19, 30, ..., 39, 50, ..., 59]

Note that since all options are disabled by default, and directives apply only
to the example they appear in, enabling options (via ``+`` in a directive) is
usually the only meaningful choice.  However, option flags can also be passed to
functions that run doctests, establishing different defaults.  In such cases,
disabling an option via ``-`` in a directive can be useful.


There's also a way to register new option flag names, although this isn't useful
unless you intend to extend :mod:`doctest` internals via subclassing:


.. function:: register_optionflag(name)

   Create a new option flag with a given name, and return the new flag's integer
   value.  :func:`register_optionflag` can be used when subclassing
   :class:`OutputChecker` or :class:`DocTestRunner` to create new options that are
   supported by your subclasses.  :func:`register_optionflag` should always be
   called using the following idiom::

      MY_FLAG = register_optionflag('MY_FLAG')


.. _doctest-warnings:

Warnings
^^^^^^^^

:mod:`doctest` is serious about requiring exact matches in expected output.  If
even a single character doesn't match, the test fails.  This will probably
surprise you a few times, as you learn exactly what Python does and doesn't
guarantee about output.  For example, when printing a dict, Python doesn't
guarantee that the key-value pairs will be printed in any particular order, so a
test like

.. % Hey! What happened to Monty Python examples?
.. % Tim: ask Guido -- it's his example!

::

   >>> foo()
   {"Hermione": "hippogryph", "Harry": "broomstick"}

is vulnerable!  One workaround is to do ::

   >>> foo() == {"Hermione": "hippogryph", "Harry": "broomstick"}
   True

instead.  Another is to do ::

   >>> d = foo().items()
   >>> d.sort()
   >>> d
   [('Harry', 'broomstick'), ('Hermione', 'hippogryph')]

There are others, but you get the idea.

Another bad idea is to print things that embed an object address, like ::

   >>> id(1.0) # certain to fail some of the time
   7948648
   >>> class C: pass
   >>> C()   # the default repr() for instances embeds an address
   <__main__.C instance at 0x00AC18F0>

The :const:`ELLIPSIS` directive gives a nice approach for the last example::

   >>> C() #doctest: +ELLIPSIS
   <__main__.C instance at 0x...>

Floating-point numbers are also subject to small output variations across
platforms, because Python defers to the platform C library for float formatting,
and C libraries vary widely in quality here. ::

   >>> 1./7  # risky
   0.14285714285714285
737
   >>> print(1./7) # safer
738
   0.142857142857
739
   >>> print(round(1./7, 6)) # much safer
740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980
   0.142857

Numbers of the form ``I/2.**J`` are safe across all platforms, and I often
contrive doctest examples to produce numbers of that form::

   >>> 3./4  # utterly safe
   0.75

Simple fractions are also easier for people to understand, and that makes for
better documentation.


.. _doctest-basic-api:

Basic API
---------

The functions :func:`testmod` and :func:`testfile` provide a simple interface to
doctest that should be sufficient for most basic uses.  For a less formal
introduction to these two functions, see sections :ref:`doctest-simple-testmod`
and :ref:`doctest-simple-testfile`.


.. function:: testfile(filename[, module_relative][, name][, package][, globs][, verbose][, report][, optionflags][, extraglobs][, raise_on_error][, parser][, encoding])

   All arguments except *filename* are optional, and should be specified in keyword
   form.

   Test examples in the file named *filename*.  Return ``(failure_count,
   test_count)``.

   Optional argument *module_relative* specifies how the filename should be
   interpreted:

   * If *module_relative* is ``True`` (the default), then *filename* specifies an
     OS-independent module-relative path.  By default, this path is relative to the
     calling module's directory; but if the *package* argument is specified, then it
     is relative to that package.  To ensure OS-independence, *filename* should use
     ``/`` characters to separate path segments, and may not be an absolute path
     (i.e., it may not begin with ``/``).

   * If *module_relative* is ``False``, then *filename* specifies an OS-specific
     path.  The path may be absolute or relative; relative paths are resolved with
     respect to the current working directory.

   Optional argument *name* gives the name of the test; by default, or if ``None``,
   ``os.path.basename(filename)`` is used.

   Optional argument *package* is a Python package or the name of a Python package
   whose directory should be used as the base directory for a module-relative
   filename.  If no package is specified, then the calling module's directory is
   used as the base directory for module-relative filenames.  It is an error to
   specify *package* if *module_relative* is ``False``.

   Optional argument *globs* gives a dict to be used as the globals when executing
   examples.  A new shallow copy of this dict is created for the doctest, so its
   examples start with a clean slate. By default, or if ``None``, a new empty dict
   is used.

   Optional argument *extraglobs* gives a dict merged into the globals used to
   execute examples.  This works like :meth:`dict.update`:  if *globs* and
   *extraglobs* have a common key, the associated value in *extraglobs* appears in
   the combined dict.  By default, or if ``None``, no extra globals are used.  This
   is an advanced feature that allows parameterization of doctests.  For example, a
   doctest can be written for a base class, using a generic name for the class,
   then reused to test any number of subclasses by passing an *extraglobs* dict
   mapping the generic name to the subclass to be tested.

   Optional argument *verbose* prints lots of stuff if true, and prints only
   failures if false; by default, or if ``None``, it's true if and only if ``'-v'``
   is in ``sys.argv``.

   Optional argument *report* prints a summary at the end when true, else prints
   nothing at the end.  In verbose mode, the summary is detailed, else the summary
   is very brief (in fact, empty if all tests passed).

   Optional argument *optionflags* or's together option flags.  See section
   :ref:`doctest-options`.

   Optional argument *raise_on_error* defaults to false.  If true, an exception is
   raised upon the first failure or unexpected exception in an example.  This
   allows failures to be post-mortem debugged. Default behavior is to continue
   running examples.

   Optional argument *parser* specifies a :class:`DocTestParser` (or subclass) that
   should be used to extract tests from the files.  It defaults to a normal parser
   (i.e., ``DocTestParser()``).

   Optional argument *encoding* specifies an encoding that should be used to
   convert the file to unicode.


.. function:: testmod([m][, name][, globs][, verbose][, report][, optionflags][, extraglobs][, raise_on_error][, exclude_empty])

   All arguments are optional, and all except for *m* should be specified in
   keyword form.

   Test examples in docstrings in functions and classes reachable from module *m*
   (or module :mod:`__main__` if *m* is not supplied or is ``None``), starting with
   ``m.__doc__``.

   Also test examples reachable from dict ``m.__test__``, if it exists and is not
   ``None``.  ``m.__test__`` maps names (strings) to functions, classes and
   strings; function and class docstrings are searched for examples; strings are
   searched directly, as if they were docstrings.

   Only docstrings attached to objects belonging to module *m* are searched.

   Return ``(failure_count, test_count)``.

   Optional argument *name* gives the name of the module; by default, or if
   ``None``, ``m.__name__`` is used.

   Optional argument *exclude_empty* defaults to false.  If true, objects for which
   no doctests are found are excluded from consideration. The default is a backward
   compatibility hack, so that code still using :meth:`doctest.master.summarize` in
   conjunction with :func:`testmod` continues to get output for objects with no
   tests. The *exclude_empty* argument to the newer :class:`DocTestFinder`
   constructor defaults to true.

   Optional arguments *extraglobs*, *verbose*, *report*, *optionflags*,
   *raise_on_error*, and *globs* are the same as for function :func:`testfile`
   above, except that *globs* defaults to ``m.__dict__``.


There's also a function to run the doctests associated with a single object.
This function is provided for backward compatibility.  There are no plans to
deprecate it, but it's rarely useful:


.. function:: run_docstring_examples(f, globs[, verbose][, name][, compileflags][, optionflags])

   Test examples associated with object *f*; for example, *f* may be a module,
   function, or class object.

   A shallow copy of dictionary argument *globs* is used for the execution context.

   Optional argument *name* is used in failure messages, and defaults to
   ``"NoName"``.

   If optional argument *verbose* is true, output is generated even if there are no
   failures.  By default, output is generated only in case of an example failure.

   Optional argument *compileflags* gives the set of flags that should be used by
   the Python compiler when running the examples.  By default, or if ``None``,
   flags are deduced corresponding to the set of future features found in *globs*.

   Optional argument *optionflags* works as for function :func:`testfile` above.


.. _doctest-unittest-api:

Unittest API
------------

As your collection of doctest'ed modules grows, you'll want a way to run all
their doctests systematically.  Prior to Python 2.4, :mod:`doctest` had a barely
documented :class:`Tester` class that supplied a rudimentary way to combine
doctests from multiple modules. :class:`Tester` was feeble, and in practice most
serious Python testing frameworks build on the :mod:`unittest` module, which
supplies many flexible ways to combine tests from multiple sources.  So, in
Python 2.4, :mod:`doctest`'s :class:`Tester` class is deprecated, and
:mod:`doctest` provides two functions that can be used to create :mod:`unittest`
test suites from modules and text files containing doctests.  These test suites
can then be run using :mod:`unittest` test runners::

   import unittest
   import doctest
   import my_module_with_doctests, and_another

   suite = unittest.TestSuite()
   for mod in my_module_with_doctests, and_another:
       suite.addTest(doctest.DocTestSuite(mod))
   runner = unittest.TextTestRunner()
   runner.run(suite)

There are two main functions for creating :class:`unittest.TestSuite` instances
from text files and modules with doctests:


.. function:: DocFileSuite([module_relative][, package][, setUp][, tearDown][, globs][, optionflags][, parser][, encoding])

   Convert doctest tests from one or more text files to a
   :class:`unittest.TestSuite`.

   The returned :class:`unittest.TestSuite` is to be run by the unittest framework
   and runs the interactive examples in each file.  If an example in any file
   fails, then the synthesized unit test fails, and a :exc:`failureException`
   exception is raised showing the name of the file containing the test and a
   (sometimes approximate) line number.

   Pass one or more paths (as strings) to text files to be examined.

   Options may be provided as keyword arguments:

   Optional argument *module_relative* specifies how the filenames in *paths*
   should be interpreted:

   * If *module_relative* is ``True`` (the default), then each filename specifies
     an OS-independent module-relative path.  By default, this path is relative to
     the calling module's directory; but if the *package* argument is specified, then
     it is relative to that package.  To ensure OS-independence, each filename should
     use ``/`` characters to separate path segments, and may not be an absolute path
     (i.e., it may not begin with ``/``).

   * If *module_relative* is ``False``, then each filename specifies an OS-specific
     path.  The path may be absolute or relative; relative paths are resolved with
     respect to the current working directory.

   Optional argument *package* is a Python package or the name of a Python package
   whose directory should be used as the base directory for module-relative
   filenames.  If no package is specified, then the calling module's directory is
   used as the base directory for module-relative filenames.  It is an error to
   specify *package* if *module_relative* is ``False``.

   Optional argument *setUp* specifies a set-up function for the test suite.  This
   is called before running the tests in each file.  The *setUp* function will be
   passed a :class:`DocTest` object.  The setUp function can access the test
   globals as the *globs* attribute of the test passed.

   Optional argument *tearDown* specifies a tear-down function for the test suite.
   This is called after running the tests in each file.  The *tearDown* function
   will be passed a :class:`DocTest` object.  The setUp function can access the
   test globals as the *globs* attribute of the test passed.

   Optional argument *globs* is a dictionary containing the initial global
   variables for the tests.  A new copy of this dictionary is created for each
   test.  By default, *globs* is a new empty dictionary.

   Optional argument *optionflags* specifies the default doctest options for the
   tests, created by or-ing together individual option flags.  See section
   :ref:`doctest-options`. See function :func:`set_unittest_reportflags` below for
   a better way to set reporting options.

   Optional argument *parser* specifies a :class:`DocTestParser` (or subclass) that
   should be used to extract tests from the files.  It defaults to a normal parser
   (i.e., ``DocTestParser()``).

   Optional argument *encoding* specifies an encoding that should be used to
   convert the file to unicode.

981 982
   The global ``__file__`` is added to the globals provided to doctests loaded
   from a text file using :func:`DocFileSuite`.
983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011


.. function:: DocTestSuite([module][, globs][, extraglobs][, test_finder][, setUp][, tearDown][, checker])

   Convert doctest tests for a module to a :class:`unittest.TestSuite`.

   The returned :class:`unittest.TestSuite` is to be run by the unittest framework
   and runs each doctest in the module.  If any of the doctests fail, then the
   synthesized unit test fails, and a :exc:`failureException` exception is raised
   showing the name of the file containing the test and a (sometimes approximate)
   line number.

   Optional argument *module* provides the module to be tested.  It can be a module
   object or a (possibly dotted) module name.  If not specified, the module calling
   this function is used.

   Optional argument *globs* is a dictionary containing the initial global
   variables for the tests.  A new copy of this dictionary is created for each
   test.  By default, *globs* is a new empty dictionary.

   Optional argument *extraglobs* specifies an extra set of global variables, which
   is merged into *globs*.  By default, no extra globals are used.

   Optional argument *test_finder* is the :class:`DocTestFinder` object (or a
   drop-in replacement) that is used to extract doctests from the module.

   Optional arguments *setUp*, *tearDown*, and *optionflags* are the same as for
   function :func:`DocFileSuite` above.

1012
   This function uses the same search technique as :func:`testmod`.
1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072


Under the covers, :func:`DocTestSuite` creates a :class:`unittest.TestSuite` out
of :class:`doctest.DocTestCase` instances, and :class:`DocTestCase` is a
subclass of :class:`unittest.TestCase`. :class:`DocTestCase` isn't documented
here (it's an internal detail), but studying its code can answer questions about
the exact details of :mod:`unittest` integration.

Similarly, :func:`DocFileSuite` creates a :class:`unittest.TestSuite` out of
:class:`doctest.DocFileCase` instances, and :class:`DocFileCase` is a subclass
of :class:`DocTestCase`.

So both ways of creating a :class:`unittest.TestSuite` run instances of
:class:`DocTestCase`.  This is important for a subtle reason: when you run
:mod:`doctest` functions yourself, you can control the :mod:`doctest` options in
use directly, by passing option flags to :mod:`doctest` functions.  However, if
you're writing a :mod:`unittest` framework, :mod:`unittest` ultimately controls
when and how tests get run.  The framework author typically wants to control
:mod:`doctest` reporting options (perhaps, e.g., specified by command line
options), but there's no way to pass options through :mod:`unittest` to
:mod:`doctest` test runners.

For this reason, :mod:`doctest` also supports a notion of :mod:`doctest`
reporting flags specific to :mod:`unittest` support, via this function:


.. function:: set_unittest_reportflags(flags)

   Set the :mod:`doctest` reporting flags to use.

   Argument *flags* or's together option flags.  See section
   :ref:`doctest-options`.  Only "reporting flags" can be used.

   This is a module-global setting, and affects all future doctests run by module
   :mod:`unittest`:  the :meth:`runTest` method of :class:`DocTestCase` looks at
   the option flags specified for the test case when the :class:`DocTestCase`
   instance was constructed.  If no reporting flags were specified (which is the
   typical and expected case), :mod:`doctest`'s :mod:`unittest` reporting flags are
   or'ed into the option flags, and the option flags so augmented are passed to the
   :class:`DocTestRunner` instance created to run the doctest.  If any reporting
   flags were specified when the :class:`DocTestCase` instance was constructed,
   :mod:`doctest`'s :mod:`unittest` reporting flags are ignored.

   The value of the :mod:`unittest` reporting flags in effect before the function
   was called is returned by the function.


.. _doctest-advanced-api:

Advanced API
------------

The basic API is a simple wrapper that's intended to make doctest easy to use.
It is fairly flexible, and should meet most users' needs; however, if you
require more fine-grained control over testing, or wish to extend doctest's
capabilities, then you should use the advanced API.

The advanced API revolves around two container classes, which are used to store
the interactive examples extracted from doctest cases:

1073 1074
* :class:`Example`: A single python :term:`statement`, paired with its expected
  output.
1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509

* :class:`DocTest`: A collection of :class:`Example`\ s, typically extracted
  from a single docstring or text file.

Additional processing classes are defined to find, parse, and run, and check
doctest examples:

* :class:`DocTestFinder`: Finds all docstrings in a given module, and uses a
  :class:`DocTestParser` to create a :class:`DocTest` from every docstring that
  contains interactive examples.

* :class:`DocTestParser`: Creates a :class:`DocTest` object from a string (such
  as an object's docstring).

* :class:`DocTestRunner`: Executes the examples in a :class:`DocTest`, and uses
  an :class:`OutputChecker` to verify their output.

* :class:`OutputChecker`: Compares the actual output from a doctest example with
  the expected output, and decides whether they match.

The relationships among these processing classes are summarized in the following
diagram::

                               list of:
   +------+                   +---------+
   |module| --DocTestFinder-> | DocTest | --DocTestRunner-> results
   +------+    |        ^     +---------+     |       ^    (printed)
               |        |     | Example |     |       |
               v        |     |   ...   |     v       |
              DocTestParser   | Example |   OutputChecker
                              +---------+


.. _doctest-doctest:

DocTest Objects
^^^^^^^^^^^^^^^


.. class:: DocTest(examples, globs, name, filename, lineno, docstring)

   A collection of doctest examples that should be run in a single namespace.  The
   constructor arguments are used to initialize the member variables of the same
   names.


:class:`DocTest` defines the following member variables.  They are initialized
by the constructor, and should not be modified directly.


.. attribute:: DocTest.examples

   A list of :class:`Example` objects encoding the individual interactive Python
   examples that should be run by this test.


.. attribute:: DocTest.globs

   The namespace (aka globals) that the examples should be run in. This is a
   dictionary mapping names to values.  Any changes to the namespace made by the
   examples (such as binding new variables) will be reflected in :attr:`globs`
   after the test is run.


.. attribute:: DocTest.name

   A string name identifying the :class:`DocTest`.  Typically, this is the name of
   the object or file that the test was extracted from.


.. attribute:: DocTest.filename

   The name of the file that this :class:`DocTest` was extracted from; or ``None``
   if the filename is unknown, or if the :class:`DocTest` was not extracted from a
   file.


.. attribute:: DocTest.lineno

   The line number within :attr:`filename` where this :class:`DocTest` begins, or
   ``None`` if the line number is unavailable.  This line number is zero-based with
   respect to the beginning of the file.


.. attribute:: DocTest.docstring

   The string that the test was extracted from, or 'None' if the string is
   unavailable, or if the test was not extracted from a string.


.. _doctest-example:

Example Objects
^^^^^^^^^^^^^^^


.. class:: Example(source, want[, exc_msg][, lineno][, indent][, options])

   A single interactive example, consisting of a Python statement and its expected
   output.  The constructor arguments are used to initialize the member variables
   of the same names.


:class:`Example` defines the following member variables.  They are initialized
by the constructor, and should not be modified directly.


.. attribute:: Example.source

   A string containing the example's source code.  This source code consists of a
   single Python statement, and always ends with a newline; the constructor adds a
   newline when necessary.


.. attribute:: Example.want

   The expected output from running the example's source code (either from stdout,
   or a traceback in case of exception).  :attr:`want` ends with a newline unless
   no output is expected, in which case it's an empty string.  The constructor adds
   a newline when necessary.


.. attribute:: Example.exc_msg

   The exception message generated by the example, if the example is expected to
   generate an exception; or ``None`` if it is not expected to generate an
   exception.  This exception message is compared against the return value of
   :func:`traceback.format_exception_only`.  :attr:`exc_msg` ends with a newline
   unless it's ``None``.  The constructor adds a newline if needed.


.. attribute:: Example.lineno

   The line number within the string containing this example where the example
   begins.  This line number is zero-based with respect to the beginning of the
   containing string.


.. attribute:: Example.indent

   The example's indentation in the containing string, i.e., the number of space
   characters that precede the example's first prompt.


.. attribute:: Example.options

   A dictionary mapping from option flags to ``True`` or ``False``, which is used
   to override default options for this example.  Any option flags not contained in
   this dictionary are left at their default value (as specified by the
   :class:`DocTestRunner`'s :attr:`optionflags`). By default, no options are set.


.. _doctest-doctestfinder:

DocTestFinder objects
^^^^^^^^^^^^^^^^^^^^^


.. class:: DocTestFinder([verbose][, parser][, recurse][, exclude_empty])

   A processing class used to extract the :class:`DocTest`\ s that are relevant to
   a given object, from its docstring and the docstrings of its contained objects.
   :class:`DocTest`\ s can currently be extracted from the following object types:
   modules, functions, classes, methods, staticmethods, classmethods, and
   properties.

   The optional argument *verbose* can be used to display the objects searched by
   the finder.  It defaults to ``False`` (no output).

   The optional argument *parser* specifies the :class:`DocTestParser` object (or a
   drop-in replacement) that is used to extract doctests from docstrings.

   If the optional argument *recurse* is false, then :meth:`DocTestFinder.find`
   will only examine the given object, and not any contained objects.

   If the optional argument *exclude_empty* is false, then
   :meth:`DocTestFinder.find` will include tests for objects with empty docstrings.


:class:`DocTestFinder` defines the following method:


.. method:: DocTestFinder.find(obj[, name][, module][, globs][, extraglobs])

   Return a list of the :class:`DocTest`\ s that are defined by *obj*'s docstring,
   or by any of its contained objects' docstrings.

   The optional argument *name* specifies the object's name; this name will be used
   to construct names for the returned :class:`DocTest`\ s.  If *name* is not
   specified, then ``obj.__name__`` is used.

   The optional parameter *module* is the module that contains the given object.
   If the module is not specified or is None, then the test finder will attempt to
   automatically determine the correct module.  The object's module is used:

   * As a default namespace, if *globs* is not specified.

   * To prevent the DocTestFinder from extracting DocTests from objects that are
     imported from other modules.  (Contained objects with modules other than
     *module* are ignored.)

   * To find the name of the file containing the object.

   * To help find the line number of the object within its file.

   If *module* is ``False``, no attempt to find the module will be made.  This is
   obscure, of use mostly in testing doctest itself: if *module* is ``False``, or
   is ``None`` but cannot be found automatically, then all objects are considered
   to belong to the (non-existent) module, so all contained objects will
   (recursively) be searched for doctests.

   The globals for each :class:`DocTest` is formed by combining *globs* and
   *extraglobs* (bindings in *extraglobs* override bindings in *globs*).  A new
   shallow copy of the globals dictionary is created for each :class:`DocTest`.  If
   *globs* is not specified, then it defaults to the module's *__dict__*, if
   specified, or ``{}`` otherwise.  If *extraglobs* is not specified, then it
   defaults to ``{}``.


.. _doctest-doctestparser:

DocTestParser objects
^^^^^^^^^^^^^^^^^^^^^


.. class:: DocTestParser()

   A processing class used to extract interactive examples from a string, and use
   them to create a :class:`DocTest` object.


:class:`DocTestParser` defines the following methods:


.. method:: DocTestParser.get_doctest(string, globs, name, filename, lineno)

   Extract all doctest examples from the given string, and collect them into a
   :class:`DocTest` object.

   *globs*, *name*, *filename*, and *lineno* are attributes for the new
   :class:`DocTest` object.  See the documentation for :class:`DocTest` for more
   information.


.. method:: DocTestParser.get_examples(string[, name])

   Extract all doctest examples from the given string, and return them as a list of
   :class:`Example` objects.  Line numbers are 0-based.  The optional argument
   *name* is a name identifying this string, and is only used for error messages.


.. method:: DocTestParser.parse(string[, name])

   Divide the given string into examples and intervening text, and return them as a
   list of alternating :class:`Example`\ s and strings. Line numbers for the
   :class:`Example`\ s are 0-based.  The optional argument *name* is a name
   identifying this string, and is only used for error messages.


.. _doctest-doctestrunner:

DocTestRunner objects
^^^^^^^^^^^^^^^^^^^^^


.. class:: DocTestRunner([checker][, verbose][, optionflags])

   A processing class used to execute and verify the interactive examples in a
   :class:`DocTest`.

   The comparison between expected outputs and actual outputs is done by an
   :class:`OutputChecker`.  This comparison may be customized with a number of
   option flags; see section :ref:`doctest-options` for more information.  If the
   option flags are insufficient, then the comparison may also be customized by
   passing a subclass of :class:`OutputChecker` to the constructor.

   The test runner's display output can be controlled in two ways. First, an output
   function can be passed to :meth:`TestRunner.run`; this function will be called
   with strings that should be displayed.  It defaults to ``sys.stdout.write``.  If
   capturing the output is not sufficient, then the display output can be also
   customized by subclassing DocTestRunner, and overriding the methods
   :meth:`report_start`, :meth:`report_success`,
   :meth:`report_unexpected_exception`, and :meth:`report_failure`.

   The optional keyword argument *checker* specifies the :class:`OutputChecker`
   object (or drop-in replacement) that should be used to compare the expected
   outputs to the actual outputs of doctest examples.

   The optional keyword argument *verbose* controls the :class:`DocTestRunner`'s
   verbosity.  If *verbose* is ``True``, then information is printed about each
   example, as it is run.  If *verbose* is ``False``, then only failures are
   printed.  If *verbose* is unspecified, or ``None``, then verbose output is used
   iff the command-line switch :option:`-v` is used.

   The optional keyword argument *optionflags* can be used to control how the test
   runner compares expected output to actual output, and how it displays failures.
   For more information, see section :ref:`doctest-options`.


:class:`DocTestParser` defines the following methods:


.. method:: DocTestRunner.report_start(out, test, example)

   Report that the test runner is about to process the given example. This method
   is provided to allow subclasses of :class:`DocTestRunner` to customize their
   output; it should not be called directly.

   *example* is the example about to be processed.  *test* is the test containing
   *example*.  *out* is the output function that was passed to
   :meth:`DocTestRunner.run`.


.. method:: DocTestRunner.report_success(out, test, example, got)

   Report that the given example ran successfully.  This method is provided to
   allow subclasses of :class:`DocTestRunner` to customize their output; it should
   not be called directly.

   *example* is the example about to be processed.  *got* is the actual output from
   the example.  *test* is the test containing *example*.  *out* is the output
   function that was passed to :meth:`DocTestRunner.run`.


.. method:: DocTestRunner.report_failure(out, test, example, got)

   Report that the given example failed.  This method is provided to allow
   subclasses of :class:`DocTestRunner` to customize their output; it should not be
   called directly.

   *example* is the example about to be processed.  *got* is the actual output from
   the example.  *test* is the test containing *example*.  *out* is the output
   function that was passed to :meth:`DocTestRunner.run`.


.. method:: DocTestRunner.report_unexpected_exception(out, test, example, exc_info)

   Report that the given example raised an unexpected exception. This method is
   provided to allow subclasses of :class:`DocTestRunner` to customize their
   output; it should not be called directly.

   *example* is the example about to be processed. *exc_info* is a tuple containing
   information about the unexpected exception (as returned by
   :func:`sys.exc_info`). *test* is the test containing *example*.  *out* is the
   output function that was passed to :meth:`DocTestRunner.run`.


.. method:: DocTestRunner.run(test[, compileflags][, out][, clear_globs])

   Run the examples in *test* (a :class:`DocTest` object), and display the results
   using the writer function *out*.

   The examples are run in the namespace ``test.globs``.  If *clear_globs* is true
   (the default), then this namespace will be cleared after the test runs, to help
   with garbage collection. If you would like to examine the namespace after the
   test completes, then use *clear_globs=False*.

   *compileflags* gives the set of flags that should be used by the Python compiler
   when running the examples.  If not specified, then it will default to the set of
   future-import flags that apply to *globs*.

   The output of each example is checked using the :class:`DocTestRunner`'s output
   checker, and the results are formatted by the :meth:`DocTestRunner.report_\*`
   methods.


.. method:: DocTestRunner.summarize([verbose])

   Print a summary of all the test cases that have been run by this DocTestRunner,
   and return a tuple ``(failure_count, test_count)``.

   The optional *verbose* argument controls how detailed the summary is.  If the
   verbosity is not specified, then the :class:`DocTestRunner`'s verbosity is used.


.. _doctest-outputchecker:

OutputChecker objects
^^^^^^^^^^^^^^^^^^^^^


.. class:: OutputChecker()

   A class used to check the whether the actual output from a doctest example
   matches the expected output.  :class:`OutputChecker` defines two methods:
   :meth:`check_output`, which compares a given pair of outputs, and returns true
   if they match; and :meth:`output_difference`, which returns a string describing
   the differences between two outputs.


:class:`OutputChecker` defines the following methods:

.. method:: OutputChecker.check_output(want, got, optionflags)

   Return ``True`` iff the actual output from an example (*got*) matches the
   expected output (*want*).  These strings are always considered to match if they
   are identical; but depending on what option flags the test runner is using,
   several non-exact match types are also possible.  See section
   :ref:`doctest-options` for more information about option flags.


.. method:: OutputChecker.output_difference(example, got, optionflags)

   Return a string describing the differences between the expected output for a
   given example (*example*) and the actual output (*got*).  *optionflags* is the
   set of option flags used to compare *want* and *got*.


.. _doctest-debugging:

Debugging
---------

Doctest provides several mechanisms for debugging doctest examples:

* Several functions convert doctests to executable Python programs, which can be
  run under the Python debugger, :mod:`pdb`.

* The :class:`DebugRunner` class is a subclass of :class:`DocTestRunner` that
  raises an exception for the first failing example, containing information about
  that example. This information can be used to perform post-mortem debugging on
  the example.

* The :mod:`unittest` cases generated by :func:`DocTestSuite` support the
  :meth:`debug` method defined by :class:`unittest.TestCase`.

* You can add a call to :func:`pdb.set_trace` in a doctest example, and you'll
  drop into the Python debugger when that line is executed.  Then you can inspect
  current values of variables, and so on.  For example, suppose :file:`a.py`
  contains just this module docstring::

     """
     >>> def f(x):
     ...     g(x*2)
     >>> def g(x):
1510
     ...     print(x+3)
1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524
     ...     import pdb; pdb.set_trace()
     >>> f(3)
     9
     """

  Then an interactive Python session may look like this::

     >>> import a, doctest
     >>> doctest.testmod(a)
     --Return--
     > <doctest a[1]>(3)g()->None
     -> import pdb; pdb.set_trace()
     (Pdb) list
       1     def g(x):
1525
       2         print(x+3)
1526 1527
       3  ->     import pdb; pdb.set_trace()
     [EOF]
1528
     (Pdb) p x
1529 1530 1531 1532 1533 1534 1535 1536 1537
     6
     (Pdb) step
     --Return--
     > <doctest a[0]>(2)f()->None
     -> g(x*2)
     (Pdb) list
       1     def f(x):
       2  ->     g(x*2)
     [EOF]
1538
     (Pdb) p x
1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562
     3
     (Pdb) step
     --Return--
     > <doctest a[2]>(1)?()->None
     -> f(3)
     (Pdb) cont
     (0, 3)
     >>>


Functions that convert doctests to Python code, and possibly run the synthesized
code under the debugger:


.. function:: script_from_examples(s)

   Convert text with examples to a script.

   Argument *s* is a string containing doctest examples.  The string is converted
   to a Python script, where doctest examples in *s* are converted to regular code,
   and everything else is converted to Python comments.  The generated script is
   returned as a string. For example, ::

      import doctest
1563
      print(doctest.script_from_examples(r"""
1564 1565 1566 1567
          Set x and y to 1 and 2.
          >>> x, y = 1, 2

          Print their sum:
1568
          >>> print(x+y)
1569
          3
1570
      """))
1571 1572 1573 1574 1575 1576 1577

   displays::

      # Set x and y to 1 and 2.
      x, y = 1, 2
      #
      # Print their sum:
1578
      print(x+y)
1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598
      # Expected:
      ## 3

   This function is used internally by other functions (see below), but can also be
   useful when you want to transform an interactive Python session into a Python
   script.


.. function:: testsource(module, name)

   Convert the doctest for an object to a script.

   Argument *module* is a module object, or dotted name of a module, containing the
   object whose doctests are of interest.  Argument *name* is the name (within the
   module) of the object with the doctests of interest.  The result is a string,
   containing the object's docstring converted to a Python script, as described for
   :func:`script_from_examples` above.  For example, if module :file:`a.py`
   contains a top-level function :func:`f`, then ::

      import a, doctest
1599
      print(doctest.testsource(a, "a.f"))
1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774

   prints a script version of function :func:`f`'s docstring, with doctests
   converted to code, and the rest placed in comments.


.. function:: debug(module, name[, pm])

   Debug the doctests for an object.

   The *module* and *name* arguments are the same as for function
   :func:`testsource` above.  The synthesized Python script for the named object's
   docstring is written to a temporary file, and then that file is run under the
   control of the Python debugger, :mod:`pdb`.

   A shallow copy of ``module.__dict__`` is used for both local and global
   execution context.

   Optional argument *pm* controls whether post-mortem debugging is used.  If *pm*
   has a true value, the script file is run directly, and the debugger gets
   involved only if the script terminates via raising an unhandled exception.  If
   it does, then post-mortem debugging is invoked, via :func:`pdb.post_mortem`,
   passing the traceback object from the unhandled exception.  If *pm* is not
   specified, or is false, the script is run under the debugger from the start, via
   passing an appropriate :func:`exec` call to :func:`pdb.run`.


.. function:: debug_src(src[, pm][, globs])

   Debug the doctests in a string.

   This is like function :func:`debug` above, except that a string containing
   doctest examples is specified directly, via the *src* argument.

   Optional argument *pm* has the same meaning as in function :func:`debug` above.

   Optional argument *globs* gives a dictionary to use as both local and global
   execution context.  If not specified, or ``None``, an empty dictionary is used.
   If specified, a shallow copy of the dictionary is used.


The :class:`DebugRunner` class, and the special exceptions it may raise, are of
most interest to testing framework authors, and will only be sketched here.  See
the source code, and especially :class:`DebugRunner`'s docstring (which is a
doctest!) for more details:


.. class:: DebugRunner([checker][, verbose][, optionflags])

   A subclass of :class:`DocTestRunner` that raises an exception as soon as a
   failure is encountered.  If an unexpected exception occurs, an
   :exc:`UnexpectedException` exception is raised, containing the test, the
   example, and the original exception.  If the output doesn't match, then a
   :exc:`DocTestFailure` exception is raised, containing the test, the example, and
   the actual output.

   For information about the constructor parameters and methods, see the
   documentation for :class:`DocTestRunner` in section :ref:`doctest-advanced-api`.

There are two exceptions that may be raised by :class:`DebugRunner` instances:


.. exception:: DocTestFailure(test, example, got)

   An exception thrown by :class:`DocTestRunner` to signal that a doctest example's
   actual output did not match its expected output. The constructor arguments are
   used to initialize the member variables of the same names.

:exc:`DocTestFailure` defines the following member variables:


.. attribute:: DocTestFailure.test

   The :class:`DocTest` object that was being run when the example failed.


.. attribute:: DocTestFailure.example

   The :class:`Example` that failed.


.. attribute:: DocTestFailure.got

   The example's actual output.


.. exception:: UnexpectedException(test, example, exc_info)

   An exception thrown by :class:`DocTestRunner` to signal that a doctest example
   raised an unexpected exception.  The constructor arguments are used to
   initialize the member variables of the same names.

:exc:`UnexpectedException` defines the following member variables:


.. attribute:: UnexpectedException.test

   The :class:`DocTest` object that was being run when the example failed.


.. attribute:: UnexpectedException.example

   The :class:`Example` that failed.


.. attribute:: UnexpectedException.exc_info

   A tuple containing information about the unexpected exception, as returned by
   :func:`sys.exc_info`.


.. _doctest-soapbox:

Soapbox
-------

As mentioned in the introduction, :mod:`doctest` has grown to have three primary
uses:

#. Checking examples in docstrings.

#. Regression testing.

#. Executable documentation / literate testing.

These uses have different requirements, and it is important to distinguish them.
In particular, filling your docstrings with obscure test cases makes for bad
documentation.

When writing a docstring, choose docstring examples with care. There's an art to
this that needs to be learned---it may not be natural at first.  Examples should
add genuine value to the documentation.  A good example can often be worth many
words. If done with care, the examples will be invaluable for your users, and
will pay back the time it takes to collect them many times over as the years go
by and things change.  I'm still amazed at how often one of my :mod:`doctest`
examples stops working after a "harmless" change.

Doctest also makes an excellent tool for regression testing, especially if you
don't skimp on explanatory text.  By interleaving prose and examples, it becomes
much easier to keep track of what's actually being tested, and why.  When a test
fails, good prose can make it much easier to figure out what the problem is, and
how it should be fixed.  It's true that you could write extensive comments in
code-based testing, but few programmers do. Many have found that using doctest
approaches instead leads to much clearer tests.  Perhaps this is simply because
doctest makes writing prose a little easier than writing code, while writing
comments in code is a little harder.  I think it goes deeper than just that:
the natural attitude when writing a doctest-based test is that you want to
explain the fine points of your software, and illustrate them with examples.
This in turn naturally leads to test files that start with the simplest
features, and logically progress to complications and edge cases.  A coherent
narrative is the result, instead of a collection of isolated functions that test
isolated bits of functionality seemingly at random.  It's a different attitude,
and produces different results, blurring the distinction between testing and
explaining.

Regression testing is best confined to dedicated objects or files.  There are
several options for organizing tests:

* Write text files containing test cases as interactive examples, and test the
  files using :func:`testfile` or :func:`DocFileSuite`.  This is recommended,
  although is easiest to do for new projects, designed from the start to use
  doctest.

* Define functions named ``_regrtest_topic`` that consist of single docstrings,
  containing test cases for the named topics.  These functions can be included in
  the same file as the module, or separated out into a separate test file.

* Define a ``__test__`` dictionary mapping from regression test topics to
  docstrings containing test cases.

.. rubric:: Footnotes

.. [#] Examples containing both expected output and an exception are not supported.
   Trying to guess where one ends and the other begins is too error-prone, and that
   also makes for a confusing test.