Commit 96593ed3 authored by Georg Brandl's avatar Georg Brandl

Continue going through the language reference, bringing it up-to-date.

In particular, document the new comprehensions and remove mentions of long integers.
Fix a bunch of related things in the lib ref.
parent 44fa8f65
...@@ -5,6 +5,11 @@ Built-in Constants ...@@ -5,6 +5,11 @@ Built-in Constants
A small number of constants live in the built-in namespace. They are: A small number of constants live in the built-in namespace. They are:
.. note::
:data:`None`, :data:`False`, :data:`True` and :data:`__debug__` cannot be
reassigned, so they can be considered "true" constants.
.. XXX False, True, None are keywords too .. XXX False, True, None are keywords too
.. data:: False .. data:: False
...@@ -37,3 +42,10 @@ A small number of constants live in the built-in namespace. They are: ...@@ -37,3 +42,10 @@ A small number of constants live in the built-in namespace. They are:
slicing syntax for user-defined container data types, as in :: slicing syntax for user-defined container data types, as in ::
val = container[1:5, 7:10, ...] val = container[1:5, 7:10, ...]
.. data:: __debug__
A boolean value that is :data:`True` if Python was not started with the
``-O`` command line option. Its value is used indirectly by the
:keyword:`assert` statement, but it can also be used directly in code.
...@@ -19,10 +19,10 @@ The typical use is:: ...@@ -19,10 +19,10 @@ The typical use is::
This iterates over the lines of all files listed in ``sys.argv[1:]``, defaulting This iterates over the lines of all files listed in ``sys.argv[1:]``, defaulting
to ``sys.stdin`` if the list is empty. If a filename is ``'-'``, it is also to ``sys.stdin`` if the list is empty. If a filename is ``'-'``, it is also
replaced by ``sys.stdin``. To specify an alternative list of filenames, pass it replaced by ``sys.stdin``. To specify an alternative list of filenames, pass it
as the first argument to :func:`input`. A single file name is also allowed. as the first argument to :func:`.input`. A single file name is also allowed.
All files are opened in text mode by default, but you can override this by All files are opened in text mode by default, but you can override this by
specifying the *mode* parameter in the call to :func:`input` or specifying the *mode* parameter in the call to :func:`.input` or
:class:`FileInput()`. If an I/O error occurs during opening or reading a file, :class:`FileInput()`. If an I/O error occurs during opening or reading a file,
:exc:`IOError` is raised. :exc:`IOError` is raised.
......
...@@ -50,4 +50,4 @@ The :mod:`new` module defines the following functions: ...@@ -50,4 +50,4 @@ The :mod:`new` module defines the following functions:
This function returns a new class object, with name *name*, derived from This function returns a new class object, with name *name*, derived from
*baseclasses* (which should be a tuple of classes) and with namespace *dict*. *baseclasses* (which should be a tuple of classes) and with namespace *dict*.
Alias for the built-in :class:`type`.
...@@ -12,8 +12,8 @@ The :mod:`readline` module defines a number of functions to facilitate ...@@ -12,8 +12,8 @@ The :mod:`readline` module defines a number of functions to facilitate
completion and reading/writing of history files from the Python interpreter. completion and reading/writing of history files from the Python interpreter.
This module can be used directly or via the :mod:`rlcompleter` module. Settings This module can be used directly or via the :mod:`rlcompleter` module. Settings
made using this module affect the behaviour of both the interpreter's made using this module affect the behaviour of both the interpreter's
interactive prompt and the prompts offered by the :func:`raw_input` and interactive prompt and the prompts offered by the built-in :func:`input`
:func:`input` built-in functions. function.
The :mod:`readline` module defines the following functions: The :mod:`readline` module defines the following functions:
......
...@@ -26,17 +26,16 @@ Naming and binding ...@@ -26,17 +26,16 @@ Naming and binding
Each occurrence of a name in the program text refers to the :dfn:`binding` of Each occurrence of a name in the program text refers to the :dfn:`binding` of
that name established in the innermost function block containing the use. that name established in the innermost function block containing the use.
.. index:: single: block .. index:: block
A :dfn:`block` is a piece of Python program text that is executed as a unit. A :dfn:`block` is a piece of Python program text that is executed as a unit.
The following are blocks: a module, a function body, and a class definition. The following are blocks: a module, a function body, and a class definition.
Each command typed interactively is a block. A script file (a file given as Each command typed interactively is a block. A script file (a file given as
standard input to the interpreter or specified on the interpreter command line standard input to the interpreter or specified on the interpreter command line
the first argument) is a code block. A script command (a command specified on the first argument) is a code block. A script command (a command specified on
the interpreter command line with the '**-c**' option) is a code block. The string the interpreter command line with the '**-c**' option) is a code block. The
argument passed to the built-in functions :func:`eval` and :func:`exec` is a string argument passed to the built-in functions :func:`eval` and :func:`exec`
code block. The expression read and evaluated by the built-in function is a code block.
:func:`input` is a code block.
.. index:: pair: execution; frame .. index:: pair: execution; frame
...@@ -44,7 +43,7 @@ A code block is executed in an :dfn:`execution frame`. A frame contains some ...@@ -44,7 +43,7 @@ A code block is executed in an :dfn:`execution frame`. A frame contains some
administrative information (used for debugging) and determines where and how administrative information (used for debugging) and determines where and how
execution continues after the code block's execution has completed. execution continues after the code block's execution has completed.
.. index:: single: scope .. index:: scope
A :dfn:`scope` defines the visibility of a name within a block. If a local A :dfn:`scope` defines the visibility of a name within a block. If a local
variable is defined in a block, its scope includes that block. If the variable is defined in a block, its scope includes that block. If the
...@@ -61,10 +60,11 @@ scope. The set of all such scopes visible to a code block is called the block's ...@@ -61,10 +60,11 @@ scope. The set of all such scopes visible to a code block is called the block's
.. index:: pair: free; variable .. index:: pair: free; variable
If a name is bound in a block, it is a local variable of that block. If a name If a name is bound in a block, it is a local variable of that block, unless
is bound at the module level, it is a global variable. (The variables of the declared as :keyword:`nonlocal`. If a name is bound at the module level, it is
module code block are local and global.) If a variable is used in a code block a global variable. (The variables of the module code block are local and
but not defined there, it is a :dfn:`free variable`. global.) If a variable is used in a code block but not defined there, it is a
:dfn:`free variable`.
.. index:: .. index::
single: NameError (built-in exception) single: NameError (built-in exception)
...@@ -101,13 +101,15 @@ is subtle. Python lacks declarations and allows name binding operations to ...@@ -101,13 +101,15 @@ is subtle. Python lacks declarations and allows name binding operations to
occur anywhere within a code block. The local variables of a code block can be occur anywhere within a code block. The local variables of a code block can be
determined by scanning the entire text of the block for name binding operations. determined by scanning the entire text of the block for name binding operations.
If the global statement occurs within a block, all uses of the name specified in If the :keyword:`global` statement occurs within a block, all uses of the name
the statement refer to the binding of that name in the top-level namespace. specified in the statement refer to the binding of that name in the top-level
Names are resolved in the top-level namespace by searching the global namespace, namespace. Names are resolved in the top-level namespace by searching the
i.e. the namespace of the module containing the code block, and the builtin global namespace, i.e. the namespace of the module containing the code block,
namespace, the namespace of the module :mod:`__builtin__`. The global namespace and the builtin namespace, the namespace of the module :mod:`__builtin__`. The
is searched first. If the name is not found there, the builtin namespace is global namespace is searched first. If the name is not found there, the builtin
searched. The global statement must precede all uses of the name. namespace is searched. The global statement must precede all uses of the name.
.. XXX document "nonlocal" semantics here
.. index:: pair: restricted; execution .. index:: pair: restricted; execution
...@@ -157,13 +159,14 @@ If the wild card form of import --- ``import *`` --- is used in a function and ...@@ -157,13 +159,14 @@ If the wild card form of import --- ``import *`` --- is used in a function and
the function contains or is a nested block with free variables, the compiler the function contains or is a nested block with free variables, the compiler
will raise a :exc:`SyntaxError`. will raise a :exc:`SyntaxError`.
The :func:`eval` and :func:`exec` functions do .. XXX from * also invalid with relative imports (at least currently)
not have access to the full environment for resolving names. Names may be
resolved in the local and global namespaces of the caller. Free variables are The :func:`eval` and :func:`exec` functions do not have access to the full
not resolved in the nearest enclosing namespace, but in the global namespace. environment for resolving names. Names may be resolved in the local and global
[#]_ The :func:`exec` and :func:`eval` functions have optional namespaces of the caller. Free variables are not resolved in the nearest
arguments to override the global and local namespace. If only one namespace is enclosing namespace, but in the global namespace. [#]_ The :func:`exec` and
specified, it is used for both. :func:`eval` functions have optional arguments to override the global and local
namespace. If only one namespace is specified, it is used for both.
.. _exceptions: .. _exceptions:
...@@ -212,14 +215,10 @@ selected depending on the class of the instance: it must reference the class of ...@@ -212,14 +215,10 @@ selected depending on the class of the instance: it must reference the class of
the instance or a base class thereof. The instance can be received by the the instance or a base class thereof. The instance can be received by the
handler and can carry additional information about the exceptional condition. handler and can carry additional information about the exceptional condition.
Exceptions can also be identified by strings, in which case the
:keyword:`except` clause is selected by object identity. An arbitrary value can
be raised along with the identifying string which can be passed to the handler.
.. warning:: .. warning::
Messages to exceptions are not part of the Python API. Their contents may Exception messages are not part of the Python API. Their contents may change
change from one version of Python to the next without warning and should not be from one version of Python to the next without warning and should not be
relied on by code which will run under multiple versions of the interpreter. relied on by code which will run under multiple versions of the interpreter.
See also the description of the :keyword:`try` statement in section :ref:`try` See also the description of the :keyword:`try` statement in section :ref:`try`
...@@ -227,6 +226,6 @@ and :keyword:`raise` statement in section :ref:`raise`. ...@@ -227,6 +226,6 @@ and :keyword:`raise` statement in section :ref:`raise`.
.. rubric:: Footnotes .. rubric:: Footnotes
.. [#] This limitation occurs because the code that is executed by these operations is .. [#] This limitation occurs because the code that is executed by these operations
not available at the time the module is compiled. is not available at the time the module is compiled.
...@@ -27,25 +27,19 @@ Arithmetic conversions ...@@ -27,25 +27,19 @@ Arithmetic conversions
.. index:: pair: arithmetic; conversion .. index:: pair: arithmetic; conversion
.. XXX no coercion rules are documented anymore
When a description of an arithmetic operator below uses the phrase "the numeric When a description of an arithmetic operator below uses the phrase "the numeric
arguments are converted to a common type," the arguments are coerced using the arguments are converted to a common type," this means that the operator
coercion rules. If both arguments are standard implementation for built-in types works that way:
numeric types, the following coercions are applied:
* If either argument is a complex number, the other is converted to complex; * If either argument is a complex number, the other is converted to complex;
* otherwise, if either argument is a floating point number, the other is * otherwise, if either argument is a floating point number, the other is
converted to floating point; converted to floating point;
* otherwise, if either argument is a long integer, the other is converted to * otherwise, both must be integers and no conversion is necessary.
long integer;
* otherwise, both must be plain integers and no conversion is necessary.
Some additional rules apply for certain operators (e.g., a string left argument Some additional rules apply for certain operators (e.g., a string left argument
to the '%' operator). Extensions can define their own coercions. to the '%' operator). Extensions must define their own conversion behavior.
.. _atoms: .. _atoms:
...@@ -53,18 +47,16 @@ to the '%' operator). Extensions can define their own coercions. ...@@ -53,18 +47,16 @@ to the '%' operator). Extensions can define their own coercions.
Atoms Atoms
===== =====
.. index:: single: atom .. index:: atom
Atoms are the most basic elements of expressions. The simplest atoms are Atoms are the most basic elements of expressions. The simplest atoms are
identifiers or literals. Forms enclosed in reverse quotes or in parentheses, identifiers or literals. Forms enclosed in parentheses, brackets or braces are
brackets or braces are also categorized syntactically as atoms. The syntax for also categorized syntactically as atoms. The syntax for atoms is:
atoms is:
.. productionlist:: .. productionlist::
atom: `identifier` | `literal` | `enclosure` atom: `identifier` | `literal` | `enclosure`
enclosure: `parenth_form` | `list_display` enclosure: `parenth_form` | `list_display` | `dict_display` | `set_display`
: | `generator_expression` | `dict_display` : | `generator_expression` | `yield_atom`
: | `string_conversion` | `yield_atom`
.. _atom-identifiers: .. _atom-identifiers:
...@@ -72,9 +64,7 @@ atoms is: ...@@ -72,9 +64,7 @@ atoms is:
Identifiers (Names) Identifiers (Names)
------------------- -------------------
.. index:: .. index:: name, identifier
single: name
single: identifier
An identifier occurring as an atom is a name. See section :ref:`identifiers` An identifier occurring as an atom is a name. See section :ref:`identifiers`
for lexical definition and section :ref:`naming` for documentation of naming and for lexical definition and section :ref:`naming` for documentation of naming and
...@@ -103,9 +93,6 @@ transformed name is extremely long (longer than 255 characters), implementation ...@@ -103,9 +93,6 @@ transformed name is extremely long (longer than 255 characters), implementation
defined truncation may happen. If the class name consists only of underscores, defined truncation may happen. If the class name consists only of underscores,
no transformation is done. no transformation is done.
.. %
.. %
.. _atom-literals: .. _atom-literals:
...@@ -114,26 +101,26 @@ Literals ...@@ -114,26 +101,26 @@ Literals
.. index:: single: literal .. index:: single: literal
Python supports string literals and various numeric literals: Python supports string and bytes literals and various numeric literals:
.. productionlist:: .. productionlist::
literal: `stringliteral` | `integer` | `longinteger` literal: `stringliteral` | `bytesliteral`
: | `floatnumber` | `imagnumber` : | `integer` | `floatnumber` | `imagnumber`
Evaluation of a literal yields an object of the given type (string, integer, Evaluation of a literal yields an object of the given type (string, bytes,
long integer, floating point number, complex number) with the given value. The integer, floating point number, complex number) with the given value. The value
value may be approximated in the case of floating point and imaginary (complex) may be approximated in the case of floating point and imaginary (complex)
literals. See section :ref:`literals` for details. literals. See section :ref:`literals` for details.
.. index:: .. index::
triple: immutable; data; type triple: immutable; data; type
pair: immutable; object pair: immutable; object
All literals correspond to immutable data types, and hence the object's identity With the exception of bytes literals, these all correspond to immutable data
is less important than its value. Multiple evaluations of literals with the types, and hence the object's identity is less important than its value.
same value (either the same occurrence in the program text or a different Multiple evaluations of literals with the same value (either the same occurrence
occurrence) may obtain the same object or a different object with the same in the program text or a different occurrence) may obtain the same object or a
value. different object with the same value.
.. _parenthesized: .. _parenthesized:
...@@ -168,6 +155,35 @@ required --- allowing unparenthesized "nothing" in expressions would cause ...@@ -168,6 +155,35 @@ required --- allowing unparenthesized "nothing" in expressions would cause
ambiguities and allow common typos to pass uncaught. ambiguities and allow common typos to pass uncaught.
.. _comprehensions:
Displays for lists, sets and dictionaries
-----------------------------------------
For constructing a list, a set or a dictionary Python provides special syntax
called "displays", each of them in two flavors:
* either the container contents are listed explicitly, or
* they are computed via a set of looping and filtering instructions, called a
:dfn:`comprehension`.
Common syntax elements for comprehensions are:
.. productionlist::
comprehension: `expression` `comp_for`
comp_for: "for" `target_list` "in" `or_test` [`comp_iter`]
comp_iter: `comp_for` | `comp_if`
comp_if: "if" `expression_nocond` [`comp_iter`]
The comprehension consists of a single expression followed by at least one
:keyword:`for` clause and zero or more :keyword:`for` or :keyword:`if` clauses.
In this case, the elements of the new container are those that would be produced
by considering each of the :keyword:`for` or :keyword:`if` clauses a block,
nesting from left to right, and evaluating the expression to produce an element
each time the innermost block is reached.
.. _lists: .. _lists:
List displays List displays
...@@ -176,71 +192,41 @@ List displays ...@@ -176,71 +192,41 @@ List displays
.. index:: .. index::
pair: list; display pair: list; display
pair: list; comprehensions pair: list; comprehensions
pair: empty; list
object: list
A list display is a possibly empty series of expressions enclosed in square A list display is a possibly empty series of expressions enclosed in square
brackets: brackets:
.. productionlist:: .. productionlist::
list_display: "[" [`expression_list` | `list_comprehension`] "]" list_display: "[" [`expression_list` | `comprehension`] "]"
list_comprehension: `expression` `list_for`
list_for: "for" `target_list` "in" `old_expression_list` [`list_iter`]
old_expression_list: `old_expression` [("," `old_expression`)+ [","]]
list_iter: `list_for` | `list_if`
list_if: "if" `old_expression` [`list_iter`]
.. index:: A list display yields a new list object, the contents being specified by either
pair: list; comprehensions a list of expressions or a comprehension. When a comma-separated list of
object: list expressions is supplied, its elements are evaluated from left to right and
pair: empty; list placed into the list object in that order. When a comprehension is supplied,
the list is constructed from the elements resulting from the comprehension.
A list display yields a new list object. Its contents are specified by
providing either a list of expressions or a list comprehension. When a
comma-separated list of expressions is supplied, its elements are evaluated from
left to right and placed into the list object in that order. When a list
comprehension is supplied, it consists of a single expression followed by at
least one :keyword:`for` clause and zero or more :keyword:`for` or :keyword:`if`
clauses. In this case, the elements of the new list are those that would be
produced by considering each of the :keyword:`for` or :keyword:`if` clauses a
block, nesting from left to right, and evaluating the expression to produce a
list element each time the innermost block is reached [#]_.
.. _set:
.. _genexpr: Set displays
------------
Generator expressions .. index:: pair: set; display
--------------------- object: set
.. index:: pair: generator; expression A set display is denoted by curly braces and distinguishable from dictionary
displays by the lack of colons separating keys and values:
A generator expression is a compact generator notation in parentheses:
.. productionlist:: .. productionlist::
generator_expression: "(" `expression` `genexpr_for` ")" set_display: "{" [`expression_list` | `comprehension`] "}"
genexpr_for: "for" `target_list` "in" `or_test` [`genexpr_iter`]
genexpr_iter: `genexpr_for` | `genexpr_if`
genexpr_if: "if" `old_expression` [`genexpr_iter`]
.. index:: object: generator
A generator expression yields a new generator object. It consists of a single
expression followed by at least one :keyword:`for` clause and zero or more
:keyword:`for` or :keyword:`if` clauses. The iterating values of the new
generator are those that would be produced by considering each of the
:keyword:`for` or :keyword:`if` clauses a block, nesting from left to right, and
evaluating the expression to yield a value that is reached the innermost block
for each iteration.
Variables used in the generator expression are evaluated lazily when the
:meth:`__next__` method is called for generator object (in the same fashion as
normal generators). However, the leftmost :keyword:`for` clause is immediately
evaluated so that error produced by it can be seen before any other possible
error in the code that handles the generator expression. Subsequent
:keyword:`for` clauses cannot be evaluated immediately since they may depend on
the previous :keyword:`for` loop. For example: ``(x*y for x in range(10) for y
in bar(x))``.
The parentheses can be omitted on calls with only one argument. See section A set display yields a new mutable set object, the contents being specified by
:ref:`calls` for the detail. either a sequence of expressions or a comprehension. When a comma-separated
list of expressions is supplied, its elements are evaluated from left to right
and added to the set object. When a comprehension is supplied, the set is
constructed from the elements resulting from the comprehension.
.. _dict: .. _dict:
...@@ -249,29 +235,33 @@ Dictionary displays ...@@ -249,29 +235,33 @@ Dictionary displays
------------------- -------------------
.. index:: pair: dictionary; display .. index:: pair: dictionary; display
key, datum, key/datum pair
.. index:: object: dictionary
single: key
single: datum
single: key/datum pair
A dictionary display is a possibly empty series of key/datum pairs enclosed in A dictionary display is a possibly empty series of key/datum pairs enclosed in
curly braces: curly braces:
.. productionlist:: .. productionlist::
dict_display: "{" [`key_datum_list`] "}" dict_display: "{" [`key_datum_list` | `dict_comprehension`] "}"
key_datum_list: `key_datum` ("," `key_datum`)* [","] key_datum_list: `key_datum` ("," `key_datum`)* [","]
key_datum: `expression` ":" `expression` key_datum: `expression` ":" `expression`
dict_comprehension: `expression` ":" `expression` `comp_for`
.. index:: object: dictionary
A dictionary display yields a new dictionary object. A dictionary display yields a new dictionary object.
The key/datum pairs are evaluated from left to right to define the entries of If a comma-separated sequence of key/datum pairs is given, they are evaluated
the dictionary: each key object is used as a key into the dictionary to store from left to right to define the entries of the dictionary: each key object is
the corresponding datum. used as a key into the dictionary to store the corresponding datum. This means
that you can specify the same key multiple times in the key/datum list, and the
final dictionary's value for that key will be the last one given.
A dict comprehension, in contrast to list and set comprehensions, needs two
expressions separated with a colon followed by the usual "for" and "if" clauses.
When the comprehension is run, the resulting key and value elements are inserted
in the new dictionary in the order they are produced.
.. index:: pair: immutable; object .. index:: pair: immutable; object
hashable
Restrictions on the types of the key values are listed earlier in section Restrictions on the types of the key values are listed earlier in section
:ref:`types`. (To summarize, the key type should be hashable, which excludes :ref:`types`. (To summarize, the key type should be hashable, which excludes
...@@ -280,6 +270,36 @@ datum (textually rightmost in the display) stored for a given key value ...@@ -280,6 +270,36 @@ datum (textually rightmost in the display) stored for a given key value
prevails. prevails.
.. _genexpr:
Generator expressions
---------------------
.. index:: pair: generator; expression
object: generator
A generator expression is a compact generator notation in parentheses:
.. productionlist::
generator_expression: "(" `expression` `comp_for` ")"
A generator expression yields a new generator object. Its syntax is the same as
for comprehensions, except that it is enclosed in parentheses instead of
brackets or curly braces.
Variables used in the generator expression are evaluated lazily when the
:meth:`__next__` method is called for generator object (in the same fashion as
normal generators). However, the leftmost :keyword:`for` clause is immediately
evaluated, so that an error produced by it can be seen before any other possible
error in the code that handles the generator expression. Subsequent
:keyword:`for` clauses cannot be evaluated immediately since they may depend on
the previous :keyword:`for` loop. For example: ``(x*y for x in range(10) for y
in bar(x))``.
The parentheses can be omitted on calls with only one argument. See section
:ref:`calls` for the detail.
.. _yieldexpr: .. _yieldexpr:
Yield expressions Yield expressions
...@@ -328,16 +348,19 @@ generator function: ...@@ -328,16 +348,19 @@ generator function:
.. index:: exception: StopIteration .. index:: exception: StopIteration
.. method:: generator.next() .. method:: generator.__next__()
Starts the execution of a generator function or resumes it at the last executed Starts the execution of a generator function or resumes it at the last
:keyword:`yield` expression. When a generator function is resumed with a executed :keyword:`yield` expression. When a generator function is resumed
:meth:`next` method, the current :keyword:`yield` expression always evaluates to with a :meth:`next` method, the current :keyword:`yield` expression always
:const:`None`. The execution then continues to the next :keyword:`yield` evaluates to :const:`None`. The execution then continues to the next
expression, where the generator is suspended again, and the value of the :keyword:`yield` expression, where the generator is suspended again, and the
:token:`expression_list` is returned to :meth:`next`'s caller. If the generator value of the :token:`expression_list` is returned to :meth:`next`'s caller.
exits without yielding another value, a :exc:`StopIteration` exception is If the generator exits without yielding another value, a :exc:`StopIteration`
raised. exception is raised.
This method is normally called implicitly, e.g. by a :keyword:`for` loop, or
by the built-in :func:`next` function.
.. method:: generator.send(value) .. method:: generator.send(value)
...@@ -346,8 +369,8 @@ generator function: ...@@ -346,8 +369,8 @@ generator function:
``value`` argument becomes the result of the current :keyword:`yield` ``value`` argument becomes the result of the current :keyword:`yield`
expression. The :meth:`send` method returns the next value yielded by the expression. The :meth:`send` method returns the next value yielded by the
generator, or raises :exc:`StopIteration` if the generator exits without generator, or raises :exc:`StopIteration` if the generator exits without
yielding another value. When :meth:`send` is called to start the generator, it yielding another value. When :meth:`send` is called to start the generator,
must be called with :const:`None` as the argument, because there is no it must be called with :const:`None` as the argument, because there is no
:keyword:`yield` expression that could receieve the value. :keyword:`yield` expression that could receieve the value.
...@@ -365,12 +388,12 @@ generator function: ...@@ -365,12 +388,12 @@ generator function:
.. method:: generator.close() .. method:: generator.close()
Raises a :exc:`GeneratorExit` at the point where the generator function was Raises a :exc:`GeneratorExit` at the point where the generator function was
paused. If the generator function then raises :exc:`StopIteration` (by exiting paused. If the generator function then raises :exc:`StopIteration` (by
normally, or due to already being closed) or :exc:`GeneratorExit` (by not exiting normally, or due to already being closed) or :exc:`GeneratorExit` (by
catching the exception), close returns to its caller. If the generator yields a not catching the exception), close returns to its caller. If the generator
value, a :exc:`RuntimeError` is raised. If the generator raises any other yields a value, a :exc:`RuntimeError` is raised. If the generator raises any
exception, it is propagated to the caller. :meth:`close` does nothing if the other exception, it is propagated to the caller. :meth:`close` does nothing
generator has already exited due to an exception or normal exit. if the generator has already exited due to an exception or normal exit.
Here is a simple example that demonstrates the behavior of generators and Here is a simple example that demonstrates the behavior of generators and
generator functions:: generator functions::
...@@ -390,10 +413,10 @@ generator functions:: ...@@ -390,10 +413,10 @@ generator functions::
... print("Don't forget to clean up when 'close()' is called.") ... print("Don't forget to clean up when 'close()' is called.")
... ...
>>> generator = echo(1) >>> generator = echo(1)
>>> print(generator.next()) >>> print(next(generator))
Execution starts when 'next()' is called for the first time. Execution starts when 'next()' is called for the first time.
1 1
>>> print(generator.next()) >>> print(next(generator))
None None
>>> print(generator.send(2)) >>> print(generator.send(2))
2 2
...@@ -406,8 +429,8 @@ generator functions:: ...@@ -406,8 +429,8 @@ generator functions::
.. seealso:: .. seealso::
:pep:`0342` - Coroutines via Enhanced Generators :pep:`0342` - Coroutines via Enhanced Generators
The proposal to enhance the API and syntax of generators, making them usable as The proposal to enhance the API and syntax of generators, making them
simple coroutines. usable as simple coroutines.
.. _primaries: .. _primaries:
...@@ -442,11 +465,12 @@ An attribute reference is a primary followed by a period and a name: ...@@ -442,11 +465,12 @@ An attribute reference is a primary followed by a period and a name:
object: list object: list
The primary must evaluate to an object of a type that supports attribute The primary must evaluate to an object of a type that supports attribute
references, e.g., a module, list, or an instance. This object is then asked to references, which most objects do. This object is then asked to produce the
produce the attribute whose name is the identifier. If this attribute is not attribute whose name is the identifier (which can be customized by overriding
available, the exception :exc:`AttributeError` is raised. Otherwise, the type the :meth:`__getattr__` method). If this attribute is not available, the
and value of the object produced is determined by the object. Multiple exception :exc:`AttributeError` is raised. Otherwise, the type and value of the
evaluations of the same attribute reference may yield different objects. object produced is determined by the object. Multiple evaluations of the same
attribute reference may yield different objects.
.. _subscriptions: .. _subscriptions:
...@@ -471,19 +495,22 @@ A subscription selects an item of a sequence (string, tuple or list) or mapping ...@@ -471,19 +495,22 @@ A subscription selects an item of a sequence (string, tuple or list) or mapping
.. productionlist:: .. productionlist::
subscription: `primary` "[" `expression_list` "]" subscription: `primary` "[" `expression_list` "]"
The primary must evaluate to an object of a sequence or mapping type. The primary must evaluate to an object that supports subscription, e.g. a list
or dictionary. User-defined objects can support subscription by defining a
:meth:`__getitem__` method.
For built-in objects, there are two types of objects that support subscription:
If the primary is a mapping, the expression list must evaluate to an object If the primary is a mapping, the expression list must evaluate to an object
whose value is one of the keys of the mapping, and the subscription selects the whose value is one of the keys of the mapping, and the subscription selects the
value in the mapping that corresponds to that key. (The expression list is a value in the mapping that corresponds to that key. (The expression list is a
tuple except if it has exactly one item.) tuple except if it has exactly one item.)
If the primary is a sequence, the expression (list) must evaluate to a plain If the primary is a sequence, the expression (list) must evaluate to an integer.
integer. If this value is negative, the length of the sequence is added to it If this value is negative, the length of the sequence is added to it (so that,
(so that, e.g., ``x[-1]`` selects the last item of ``x``.) The resulting value e.g., ``x[-1]`` selects the last item of ``x``.) The resulting value must be a
must be a nonnegative integer less than the number of items in the sequence, and nonnegative integer less than the number of items in the sequence, and the
the subscription selects the item whose index is that value (counting from subscription selects the item whose index is that value (counting from zero).
zero).
.. index:: .. index::
single: character single: character
...@@ -534,15 +561,16 @@ slice list contains no proper slice). ...@@ -534,15 +561,16 @@ slice list contains no proper slice).
single: step (slice object attribute) single: step (slice object attribute)
The semantics for a slicing are as follows. The primary must evaluate to a The semantics for a slicing are as follows. The primary must evaluate to a
mapping object, and it is indexed with a key that is constructed from the mapping object, and it is indexed (using the same :meth:`__getitem__` method as
slice list, as follows. If the slice list contains at least one comma, the normal subscription) with a key that is constructed from the slice list, as
key is a tuple containing the conversion of the slice items; otherwise, the follows. If the slice list contains at least one comma, the key is a tuple
conversion of the lone slice item is the key. The conversion of a slice containing the conversion of the slice items; otherwise, the conversion of the
item that is an expression is that expression. The conversion of a proper lone slice item is the key. The conversion of a slice item that is an
slice is a slice object (see section :ref:`types`) whose :attr:`start`, expression is that expression. The conversion of a proper slice is a slice
:attr:`stop` and :attr:`step` attributes are the values of the expressions object (see section :ref:`types`) whose :attr:`start`, :attr:`stop` and
given as lower bound, upper bound and stride, respectively, substituting :attr:`step` attributes are the values of the expressions given as lower bound,
``None`` for missing expressions. upper bound and stride, respectively, substituting ``None`` for missing
expressions.
.. _calls: .. _calls:
...@@ -576,10 +604,11 @@ does not affect the semantics. ...@@ -576,10 +604,11 @@ does not affect the semantics.
The primary must evaluate to a callable object (user-defined functions, built-in The primary must evaluate to a callable object (user-defined functions, built-in
functions, methods of built-in objects, class objects, methods of class functions, methods of built-in objects, class objects, methods of class
instances, and certain class instances themselves are callable; extensions may instances, and all objects having a :meth:`__call__` method are callable). All
define additional callable object types). All argument expressions are argument expressions are evaluated before the call is attempted. Please refer
evaluated before the call is attempted. Please refer to section :ref:`function` to section :ref:`function` for the syntax of formal parameter lists.
for the syntax of formal parameter lists.
.. XXX update with kwonly args PEP
If keyword arguments are present, they are first converted to positional If keyword arguments are present, they are first converted to positional
arguments, as follows. First, a list of unfilled slots is created for the arguments, as follows. First, a list of unfilled slots is created for the
...@@ -722,16 +751,12 @@ for the operands): ``-1**2`` results in ``-1``. ...@@ -722,16 +751,12 @@ for the operands): ``-1**2`` results in ``-1``.
The power operator has the same semantics as the built-in :func:`pow` function, The power operator has the same semantics as the built-in :func:`pow` function,
when called with two arguments: it yields its left argument raised to the power when called with two arguments: it yields its left argument raised to the power
of its right argument. The numeric arguments are first converted to a common of its right argument. The numeric arguments are first converted to a common
type. The result type is that of the arguments after coercion. type, and the result is of that type.
With mixed operand types, the coercion rules for binary arithmetic operators For int operands, the result has the same type as the operands unless the second
apply. For int and long int operands, the result has the same type as the argument is negative; in that case, all arguments are converted to float and a
operands (after coercion) unless the second argument is negative; in that case, float result is delivered. For example, ``10**2`` returns ``100``, but
all arguments are converted to float and a float result is delivered. For ``10**-2`` returns ``0.01``.
example, ``10**2`` returns ``100``, but ``10**-2`` returns ``0.01``. (This last
feature was added in Python 2.2. In Python 2.1 and before, if both arguments
were of integer types and the second argument was negative, an exception was
raised).
Raising ``0.0`` to a negative power results in a :exc:`ZeroDivisionError`. Raising ``0.0`` to a negative power results in a :exc:`ZeroDivisionError`.
Raising a negative number to a fractional power results in a :exc:`ValueError`. Raising a negative number to a fractional power results in a :exc:`ValueError`.
...@@ -763,9 +788,9 @@ The unary ``+`` (plus) operator yields its numeric argument unchanged. ...@@ -763,9 +788,9 @@ The unary ``+`` (plus) operator yields its numeric argument unchanged.
.. index:: single: inversion .. index:: single: inversion
The unary ``~`` (invert) operator yields the bit-wise inversion of its plain or The unary ``~`` (invert) operator yields the bit-wise inversion of its integer
long integer argument. The bit-wise inversion of ``x`` is defined as argument. The bit-wise inversion of ``x`` is defined as ``-(x+1)``. It only
``-(x+1)``. It only applies to integral numbers. applies to integral numbers.
.. index:: exception: TypeError .. index:: exception: TypeError
...@@ -793,11 +818,10 @@ operators and one for additive operators: ...@@ -793,11 +818,10 @@ operators and one for additive operators:
.. index:: single: multiplication .. index:: single: multiplication
The ``*`` (multiplication) operator yields the product of its arguments. The The ``*`` (multiplication) operator yields the product of its arguments. The
arguments must either both be numbers, or one argument must be an integer (plain arguments must either both be numbers, or one argument must be an integer and
or long) and the other must be a sequence. In the former case, the numbers are the other must be a sequence. In the former case, the numbers are converted to a
converted to a common type and then multiplied together. In the latter case, common type and then multiplied together. In the latter case, sequence
sequence repetition is performed; a negative repetition factor yields an empty repetition is performed; a negative repetition factor yields an empty sequence.
sequence.
.. index:: .. index::
exception: ZeroDivisionError exception: ZeroDivisionError
...@@ -805,9 +829,10 @@ sequence. ...@@ -805,9 +829,10 @@ sequence.
The ``/`` (division) and ``//`` (floor division) operators yield the quotient of The ``/`` (division) and ``//`` (floor division) operators yield the quotient of
their arguments. The numeric arguments are first converted to a common type. their arguments. The numeric arguments are first converted to a common type.
Plain or long integer division yields an integer of the same type; the result is Integer division yields a float, while floor division of integers results in an
that of mathematical division with the 'floor' function applied to the result. integer; the result is that of mathematical division with the 'floor' function
Division by zero raises the :exc:`ZeroDivisionError` exception. applied to the result. Division by zero raises the :exc:`ZeroDivisionError`
exception.
.. index:: single: modulo .. index:: single: modulo
...@@ -820,21 +845,19 @@ result with the same sign as its second operand (or zero); the absolute value of ...@@ -820,21 +845,19 @@ result with the same sign as its second operand (or zero); the absolute value of
the result is strictly smaller than the absolute value of the second operand the result is strictly smaller than the absolute value of the second operand
[#]_. [#]_.
The integer division and modulo operators are connected by the following The floor division and modulo operators are connected by the following
identity: ``x == (x/y)*y + (x%y)``. Integer division and modulo are also identity: ``x == (x//y)*y + (x%y)``. Floor division and modulo are also
connected with the built-in function :func:`divmod`: ``divmod(x, y) == (x/y, connected with the built-in function :func:`divmod`: ``divmod(x, y) == (x//y,
x%y)``. These identities don't hold for floating point numbers; there similar x%y)``. [#]_.
identities hold approximately where ``x/y`` is replaced by ``floor(x/y)`` or
``floor(x/y) - 1`` [#]_.
In addition to performing the modulo operation on numbers, the ``%`` operator is In addition to performing the modulo operation on numbers, the ``%`` operator is
also overloaded by string objects to perform string formatting (also also overloaded by string objects to perform old-style string formatting (also
known as interpolation). The syntax for string formatting is described in the known as interpolation). The syntax for string formatting is described in the
Python Library Reference, section :ref:`old-string-formatting`. Python Library Reference, section :ref:`old-string-formatting`.
The floor division operator, the modulo operator, and the :func:`divmod` The floor division operator, the modulo operator, and the :func:`divmod`
function are not defined for complex numbers. Instead, convert to a function are not defined for complex numbers. Instead, convert to a floating
floating point number using the :func:`abs` function if appropriate. point number using the :func:`abs` function if appropriate.
.. index:: single: addition .. index:: single: addition
...@@ -861,17 +884,13 @@ The shifting operations have lower priority than the arithmetic operations: ...@@ -861,17 +884,13 @@ The shifting operations have lower priority than the arithmetic operations:
.. productionlist:: .. productionlist::
shift_expr: `a_expr` | `shift_expr` ( "<<" | ">>" ) `a_expr` shift_expr: `a_expr` | `shift_expr` ( "<<" | ">>" ) `a_expr`
These operators accept plain or long integers as arguments. The arguments are These operators accept integers as arguments. They shift the first argument to
converted to a common type. They shift the first argument to the left or right the left or right by the number of bits given by the second argument.
by the number of bits given by the second argument.
.. index:: exception: ValueError .. index:: exception: ValueError
A right shift by *n* bits is defined as division by ``pow(2,n)``. A left shift A right shift by *n* bits is defined as division by ``pow(2,n)``. A left shift
by *n* bits is defined as multiplication with ``pow(2,n)``; for plain integers by *n* bits is defined as multiplication with ``pow(2,n)``.
there is no overflow check so in that case the operation drops bits and flips
the sign if the result is not less than ``pow(2,31)`` in absolute value.
Negative shift counts raise a :exc:`ValueError` exception.
.. _bitwise: .. _bitwise:
...@@ -890,22 +909,22 @@ Each of the three bitwise operations has a different priority level: ...@@ -890,22 +909,22 @@ Each of the three bitwise operations has a different priority level:
.. index:: pair: bit-wise; and .. index:: pair: bit-wise; and
The ``&`` operator yields the bitwise AND of its arguments, which must be plain The ``&`` operator yields the bitwise AND of its arguments, which must be
or long integers. The arguments are converted to a common type. integers.
.. index:: .. index::
pair: bit-wise; xor pair: bit-wise; xor
pair: exclusive; or pair: exclusive; or
The ``^`` operator yields the bitwise XOR (exclusive OR) of its arguments, which The ``^`` operator yields the bitwise XOR (exclusive OR) of its arguments, which
must be plain or long integers. The arguments are converted to a common type. must be integers.
.. index:: .. index::
pair: bit-wise; or pair: bit-wise; or
pair: inclusive; or pair: inclusive; or
The ``|`` operator yields the bitwise (inclusive) OR of its arguments, which The ``|`` operator yields the bitwise (inclusive) OR of its arguments, which
must be plain or long integers. The arguments are converted to a common type. must be integers.
.. _comparisons: .. _comparisons:
...@@ -949,8 +968,8 @@ values of two objects. The objects need not have the same type. If both are ...@@ -949,8 +968,8 @@ values of two objects. The objects need not have the same type. If both are
numbers, they are converted to a common type. Otherwise, objects of different numbers, they are converted to a common type. Otherwise, objects of different
types *always* compare unequal, and are ordered consistently but arbitrarily. types *always* compare unequal, and are ordered consistently but arbitrarily.
You can control comparison behavior of objects of non-builtin types by defining You can control comparison behavior of objects of non-builtin types by defining
a ``__cmp__`` method or rich comparison methods like ``__gt__``, described in a :meth:`__cmp__` method or rich comparison methods like :meth:`__gt__`,
section :ref:`specialnames`. described in section :ref:`specialnames`.
(This unusual definition of comparison was used to simplify the definition of (This unusual definition of comparison was used to simplify the definition of
operations like sorting and the :keyword:`in` and :keyword:`not in` operators. operations like sorting and the :keyword:`in` and :keyword:`not in` operators.
...@@ -961,12 +980,12 @@ Comparison of objects of the same type depends on the type: ...@@ -961,12 +980,12 @@ Comparison of objects of the same type depends on the type:
* Numbers are compared arithmetically. * Numbers are compared arithmetically.
* Bytes objects are compared lexicographically using the numeric values of * Bytes objects are compared lexicographically using the numeric values of their
their elements. elements.
* Strings are compared lexicographically using the numeric equivalents (the * Strings are compared lexicographically using the numeric equivalents (the
result of the built-in function :func:`ord`) of their characters. [#]_ result of the built-in function :func:`ord`) of their characters. [#]_ String
String and bytes object can't be compared! and bytes object can't be compared!
* Tuples and lists are compared lexicographically using comparison of * Tuples and lists are compared lexicographically using comparison of
corresponding elements. This means that to compare equal, each element must corresponding elements. This means that to compare equal, each element must
...@@ -975,11 +994,11 @@ Comparison of objects of the same type depends on the type: ...@@ -975,11 +994,11 @@ Comparison of objects of the same type depends on the type:
If not equal, the sequences are ordered the same as their first differing If not equal, the sequences are ordered the same as their first differing
elements. For example, ``cmp([1,2,x], [1,2,y])`` returns the same as elements. For example, ``cmp([1,2,x], [1,2,y])`` returns the same as
``cmp(x,y)``. If the corresponding element does not exist, the shorter sequence ``cmp(x,y)``. If the corresponding element does not exist, the shorter
is ordered first (for example, ``[1,2] < [1,2,3]``). sequence is ordered first (for example, ``[1,2] < [1,2,3]``).
* Mappings (dictionaries) compare equal if and only if their sorted (key, value) * Mappings (dictionaries) compare equal if and only if their sorted ``(key,
lists compare equal. [#]_ Outcomes other than equality are resolved value)`` lists compare equal. [#]_ Outcomes other than equality are resolved
consistently, but are not otherwise defined. [#]_ consistently, but are not otherwise defined. [#]_
* Most other objects of builtin types compare unequal unless they are the same * Most other objects of builtin types compare unequal unless they are the same
...@@ -987,14 +1006,11 @@ Comparison of objects of the same type depends on the type: ...@@ -987,14 +1006,11 @@ Comparison of objects of the same type depends on the type:
another one is made arbitrarily but consistently within one execution of a another one is made arbitrarily but consistently within one execution of a
program. program.
The operators :keyword:`in` and :keyword:`not in` test for set membership. ``x The operators :keyword:`in` and :keyword:`not in` test for membership. ``x in
in s`` evaluates to true if *x* is a member of the set *s*, and false otherwise. s`` evaluates to true if *x* is a member of *s*, and false otherwise. ``x not
``x not in s`` returns the negation of ``x in s``. The set membership test has in s`` returns the negation of ``x in s``. All built-in sequences and set types
traditionally been bound to sequences; an object is a member of a set if the set support this as well as dictionary, for which :keyword:`in` tests whether a the
is a sequence and contains an element equal to that object. However, it is dictionary has a given key.
possible for an object to support membership tests without being a sequence. In
particular, dictionaries support membership testing as a nicer way of spelling
``key in dict``; other mapping types may follow suit.
For the list and tuple types, ``x in y`` is true if and only if there exists an For the list and tuple types, ``x in y`` is true if and only if there exists an
index *i* such that ``x == y[i]`` is true. index *i* such that ``x == y[i]`` is true.
...@@ -1045,7 +1061,7 @@ Boolean operations have the lowest priority of all Python operations: ...@@ -1045,7 +1061,7 @@ Boolean operations have the lowest priority of all Python operations:
.. productionlist:: .. productionlist::
expression: `conditional_expression` | `lambda_form` expression: `conditional_expression` | `lambda_form`
old_expression: `or_test` | `old_lambda_form` expression_nocond: `or_test` | `lambda_form_nocond`
conditional_expression: `or_test` ["if" `or_test` "else" `expression`] conditional_expression: `or_test` ["if" `or_test` "else" `expression`]
or_test: `and_test` | `or_test` "or" `and_test` or_test: `and_test` | `or_test` "or" `and_test`
and_test: `not_test` | `and_test` "and" `not_test` and_test: `not_test` | `and_test` "and" `not_test`
...@@ -1055,7 +1071,8 @@ In the context of Boolean operations, and also when expressions are used by ...@@ -1055,7 +1071,8 @@ In the context of Boolean operations, and also when expressions are used by
control flow statements, the following values are interpreted as false: control flow statements, the following values are interpreted as false:
``False``, ``None``, numeric zero of all types, and empty strings and containers ``False``, ``None``, numeric zero of all types, and empty strings and containers
(including strings, tuples, lists, dictionaries, sets and frozensets). All (including strings, tuples, lists, dictionaries, sets and frozensets). All
other values are interpreted as true. other values are interpreted as true. User-defined objects can customize their
truth value by providing a :meth:`__bool__` method.
.. index:: operator: not .. index:: operator: not
...@@ -1097,14 +1114,14 @@ Lambdas ...@@ -1097,14 +1114,14 @@ Lambdas
.. productionlist:: .. productionlist::
lambda_form: "lambda" [`parameter_list`]: `expression` lambda_form: "lambda" [`parameter_list`]: `expression`
old_lambda_form: "lambda" [`parameter_list`]: `old_expression` lambda_form_nocond: "lambda" [`parameter_list`]: `expression_nocond`
Lambda forms (lambda expressions) have the same syntactic position as Lambda forms (lambda expressions) have the same syntactic position as
expressions. They are a shorthand to create anonymous functions; the expression expressions. They are a shorthand to create anonymous functions; the expression
``lambda arguments: expression`` yields a function object. The unnamed object ``lambda arguments: expression`` yields a function object. The unnamed object
behaves like a function object defined with :: behaves like a function object defined with ::
def name(arguments): def <lambda>(arguments):
return expression return expression
See section :ref:`function` for the syntax of parameter lists. Note that See section :ref:`function` for the syntax of parameter lists. Note that
...@@ -1145,8 +1162,8 @@ Evaluation order ...@@ -1145,8 +1162,8 @@ Evaluation order
.. index:: pair: evaluation; order .. index:: pair: evaluation; order
Python evaluates expressions from left to right. Notice that while evaluating an Python evaluates expressions from left to right. Notice that while evaluating
assignment, the right-hand side is evaluated before the left-hand side. an assignment, the right-hand side is evaluated before the left-hand side.
In the following lines, expressions will be evaluated in the arithmetic order of In the following lines, expressions will be evaluated in the arithmetic order of
their suffixes:: their suffixes::
...@@ -1201,7 +1218,7 @@ groups from right to left). ...@@ -1201,7 +1218,7 @@ groups from right to left).
+----------------------------------------------+-------------------------------------+ +----------------------------------------------+-------------------------------------+
| ``+``, ``-`` | Addition and subtraction | | ``+``, ``-`` | Addition and subtraction |
+----------------------------------------------+-------------------------------------+ +----------------------------------------------+-------------------------------------+
| ``*``, ``/``, ``%`` | Multiplication, division, remainder | | ``*``, ``/``, ``//``, ``%`` | Multiplication, division, remainder |
+----------------------------------------------+-------------------------------------+ +----------------------------------------------+-------------------------------------+
| ``+x``, ``-x`` | Positive, negative | | ``+x``, ``-x`` | Positive, negative |
+----------------------------------------------+-------------------------------------+ +----------------------------------------------+-------------------------------------+
...@@ -1217,20 +1234,16 @@ groups from right to left). ...@@ -1217,20 +1234,16 @@ groups from right to left).
+----------------------------------------------+-------------------------------------+ +----------------------------------------------+-------------------------------------+
| ``f(arguments...)`` | Function call | | ``f(arguments...)`` | Function call |
+----------------------------------------------+-------------------------------------+ +----------------------------------------------+-------------------------------------+
| ``(expressions...)`` | Binding or tuple display | | ``(expressions...)`` | Binding, tuple display, generator |
| | expressions |
+----------------------------------------------+-------------------------------------+ +----------------------------------------------+-------------------------------------+
| ``[expressions...]`` | List display | | ``[expressions...]`` | List display |
+----------------------------------------------+-------------------------------------+ +----------------------------------------------+-------------------------------------+
| ``{key:datum...}`` | Dictionary display | | ``{expressions...}`` | Dictionary or set display |
+----------------------------------------------+-------------------------------------+ +----------------------------------------------+-------------------------------------+
.. rubric:: Footnotes .. rubric:: Footnotes
.. [#] In Python 2.3, a list comprehension "leaks" the control variables of each
``for`` it contains into the containing scope. However, this behavior is
deprecated, and relying on it will not work once this bug is fixed in a future
release
.. [#] While ``abs(x%y) < abs(y)`` is true mathematically, for floats it may not be .. [#] While ``abs(x%y) < abs(y)`` is true mathematically, for floats it may not be
true numerically due to roundoff. For example, and assuming a platform on which true numerically due to roundoff. For example, and assuming a platform on which
a Python float is an IEEE 754 double-precision number, in order that ``-1e-100 % a Python float is an IEEE 754 double-precision number, in order that ``-1e-100 %
...@@ -1241,22 +1254,21 @@ groups from right to left). ...@@ -1241,22 +1254,21 @@ groups from right to left).
is more appropriate depends on the application. is more appropriate depends on the application.
.. [#] If x is very close to an exact integer multiple of y, it's possible for .. [#] If x is very close to an exact integer multiple of y, it's possible for
``floor(x/y)`` to be one larger than ``(x-x%y)/y`` due to rounding. In such ``x//y`` to be one larger than ``(x-x%y)//y`` due to rounding. In such
cases, Python returns the latter result, in order to preserve that cases, Python returns the latter result, in order to preserve that
``divmod(x,y)[0] * y + x % y`` be very close to ``x``. ``divmod(x,y)[0] * y + x % y`` be very close to ``x``.
.. [#] While comparisons between strings make sense at the byte .. [#] While comparisons between strings make sense at the byte level, they may
level, they may be counter-intuitive to users. For example, the be counter-intuitive to users. For example, the strings ``"\u00C7"`` and
strings ``"\u00C7"`` and ``"\u0327\u0043"`` compare differently, ``"\u0327\u0043"`` compare differently, even though they both represent the
even though they both represent the same unicode character (LATIN same unicode character (LATIN CAPTITAL LETTER C WITH CEDILLA).
CAPTITAL LETTER C WITH CEDILLA).
.. [#] The implementation computes this efficiently, without constructing lists or .. [#] The implementation computes this efficiently, without constructing lists
sorting. or sorting.
.. [#] Earlier versions of Python used lexicographic comparison of the sorted (key, .. [#] Earlier versions of Python used lexicographic comparison of the sorted (key,
value) lists, but this was very expensive for the common case of comparing for value) lists, but this was very expensive for the common case of comparing
equality. An even earlier version of Python compared dictionaries by identity for equality. An even earlier version of Python compared dictionaries by
only, but this caused surprises because people expected to be able to test a identity only, but this caused surprises because people expected to be able
dictionary for emptiness by comparing it to ``{}``. to test a dictionary for emptiness by comparing it to ``{}``.
...@@ -106,13 +106,6 @@ string argument to :func:`eval` must have the following form: ...@@ -106,13 +106,6 @@ string argument to :func:`eval` must have the following form:
.. productionlist:: .. productionlist::
eval_input: `expression_list` NEWLINE* eval_input: `expression_list` NEWLINE*
.. index:: builtin: input
The input line read by :func:`input` must have the following form:
.. productionlist::
input_input: `expression_list` NEWLINE
.. index:: .. index::
object: file object: file
single: input; raw single: input; raw
......
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