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Commit 4b49131f authored by Georg Brandl's avatar Georg Brandl
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Commit #1068: new docs for PEP 3101. Also document the old string formatting... 

Commit #1068: new docs for PEP 3101. Also document the old string formatting as "old", and begin documenting str/unicode unification.
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Doc/library/fpformat.rst
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......@@ -12,8 +12,8 @@ numbers representations in 100% pure Python.
.. note::
This module is unnecessary: everything here can be done using the ``%`` string
interpolation operator described in the :ref:`string-formatting` section.
This module is unnecessary: everything here can be done using the string
formatting functions described in the :ref:`string-formatting` section.
The :mod:`fpformat` module defines the following functions and an exception:
......
Doc/library/functions.rst
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......@@ -449,6 +449,22 @@ available. They are listed here in alphabetical order.
The float type is described in :ref:`typesnumeric`.
.. function:: format(value[, format_spec])
.. index::
pair: str; format
single: __format__
Convert a string or a number to a "formatted" representation, as controlled
by *format_spec*. The interpretation of *format_spec* will depend on the
type of the *value* argument, however there is a standard formatting syntax
that is used by most built-in types: :ref:`formatspec`.
.. note::
``format(value, format_spec)`` merely calls ``value.__format__(format_spec)``.
.. function:: frozenset([iterable])
:noindex:
......@@ -990,10 +1006,9 @@ available. They are listed here in alphabetical order.
For more information on strings see :ref:`typesseq` which describes sequence
functionality (strings are sequences), and also the string-specific methods
described in the :ref:`string-methods` section. To output formatted strings
use template strings or the ``%`` operator described in the
:ref:`string-formatting` section. In addition see the :ref:`stringservices`
section. See also :func:`unicode`.
described in the :ref:`string-methods` section. To output formatted strings,
see the :ref:`string-formatting` section. In addition see the
:ref:`stringservices` section.
.. function:: sum(iterable[, start])
......
Doc/library/logging.rst
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......@@ -611,8 +611,10 @@ This time, all messages with a severity of DEBUG or above were handled, and the
format of the messages was also changed, and output went to the specified file
rather than the console.
Formatting uses standard Python string formatting - see section
:ref:`string-formatting`. The format string takes the following common
.. XXX logging should probably be updated!
Formatting uses the old Python string formatting - see section
:ref:`old-string-formatting`. The format string takes the following common
specifiers. For a complete list of specifiers, consult the :class:`Formatter`
documentation.
......@@ -1483,7 +1485,7 @@ A Formatter can be initialized with a format string which makes use of knowledge
of the :class:`LogRecord` attributes - such as the default value mentioned above
making use of the fact that the user's message and arguments are pre-formatted
into a :class:`LogRecord`'s *message* attribute. This format string contains
standard python %-style mapping keys. See section :ref:`string-formatting`
standard python %-style mapping keys. See section :ref:`old-string-formatting`
for more information on string formatting.
Currently, the useful mapping keys in a :class:`LogRecord` are:
......
Doc/library/stdtypes.rst
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......@@ -480,19 +480,18 @@ object) supplying the :meth:`__iter__` and :meth:`__next__` methods.
.. _typesseq:
Sequence Types --- :class:`str`, :class:`unicode`, :class:`list`, :class:`tuple`, :class:`buffer`, :class:`range`
=================================================================================================================
There are six sequence types: strings, Unicode strings, lists, tuples, buffers,
and range objects.
(For other containers see the built in :class:`dict`, :class:`list`,
:class:`set`, and :class:`tuple` classes, and the :mod:`collections`
module.)
Sequence Types --- :class:`str`, :class:`bytes`, :class:`list`, :class:`tuple`, :class:`buffer`, :class:`range`
===============================================================================================================
There are five sequence types: strings, byte sequences, lists, tuples, buffers,
and range objects. (For other containers see the built in :class:`dict`,
:class:`list`, :class:`set`, and :class:`tuple` classes, and the
:mod:`collections` module.)
.. index::
object: sequence
object: string
object: bytes
object: tuple
object: list
object: buffer
......@@ -501,21 +500,32 @@ module.)
String literals are written in single or double quotes: ``'xyzzy'``,
``"frobozz"``. See :ref:`strings` for more about string literals. In addition
to the functionality described here, there are also string-specific methods
described in the :ref:`string-methods` section. Lists are constructed with
square brackets, separating items with commas: ``[a, b, c]``. Tuples are
constructed by the comma operator (not within square brackets), with or without
enclosing parentheses, but an empty tuple must have the enclosing parentheses,
such as ``a, b, c`` or ``()``. A single item tuple must have a trailing comma,
such as ``(d,)``.
described in the :ref:`string-methods` section. Bytes objects can be
constructed from literals too; use a ``b`` prefix with normal string syntax:
``b'xyzzy'``.
.. caveat::
While string objects are sequences of characters (represented by strings of
length 1), bytes objects are sequences of *integers* (between 0 and 255),
representing the ASCII value of single bytes. That means that for a bytes
object *b*, ``b[0]`` will be an integer, while ``b[0:1]`` will be a bytes
object of length 1.
Lists are constructed with square brackets, separating items with commas: ``[a,
b, c]``. Tuples are constructed by the comma operator (not within square
brackets), with or without enclosing parentheses, but an empty tuple must have
the enclosing parentheses, such as ``a, b, c`` or ``()``. A single item tuple
must have a trailing comma, such as ``(d,)``.
Buffer objects are not directly supported by Python syntax, but can be created
by calling the builtin function :func:`buffer`. They don't support
concatenation or repetition.
Objects of type range are similar to buffers in that there is no specific syntax to
create them, but they are created using the :func:`range` function. They don't
support slicing, concatenation or repetition, and using ``in``, ``not in``,
:func:`min` or :func:`max` on them is inefficient.
Objects of type range are similar to buffers in that there is no specific syntax
to create them, but they are created using the :func:`range` function. They
don't support slicing, concatenation or repetition, and using ``in``, ``not
in``, :func:`min` or :func:`max` on them is inefficient.
Most sequence types support the following operations. The ``in`` and ``not in``
operations have the same priorities as the comparison operations. The ``+`` and
......@@ -555,12 +565,11 @@ are sequences of the same type; *n*, *i* and *j* are integers:
| ``max(s)`` | largest item of *s* | |
+------------------+--------------------------------+----------+
Sequence types also support comparisons. In particular, tuples and lists
are compared lexicographically by comparing corresponding
elements. This means that to compare equal, every element must compare
equal and the two sequences must be of the same type and have the same
length. (For full details see :ref:`comparisons` in the language
reference.)
Sequence types also support comparisons. In particular, tuples and lists are
compared lexicographically by comparing corresponding elements. This means that
to compare equal, every element must compare equal and the two sequences must be
of the same type and have the same length. (For full details see
:ref:`comparisons` in the language reference.)
.. index::
triple: operations on; sequence; types
......@@ -578,10 +587,8 @@ reference.)
Notes:
(1)
When *s* is a string or Unicode string object the ``in`` and ``not in``
operations act like a substring test. In Python versions before 2.3, *x* had to
be a string of length 1. In Python 2.3 and beyond, *x* may be a string of any
length.
When *s* is a string object, the ``in`` and ``not in`` operations act like a
substring test.
(2)
Values of *n* less than ``0`` are treated as ``0`` (which yields an empty
......@@ -642,6 +649,8 @@ Notes:
Formerly, string concatenation never occurred in-place.
.. XXX add bytes methods
.. _string-methods:
String Methods
......@@ -649,19 +658,15 @@ String Methods
.. index:: pair: string; methods
Below are listed the string methods which both 8-bit strings and Unicode objects
support. In addition, Python's strings support the sequence type methods
described in the :ref:`typesseq` section. To output formatted strings
use template strings or the ``%`` operator described in the
:ref:`string-formatting` section. Also, see the :mod:`re` module for
string functions based on regular expressions.
String objects support the methods listed below. In addition, Python's strings
support the sequence type methods described in the :ref:`typesseq` section. To
output formatted strings, see the :ref:`string-formatting` section. Also, see
the :mod:`re` module for string functions based on regular expressions.
.. method:: str.capitalize()
Return a copy of the string with only its first character capitalized.
For 8-bit strings, this method is locale-dependent.
.. method:: str.center(width[, fillchar])
......@@ -679,6 +684,7 @@ string functions based on regular expressions.
slice notation.
.. XXX what about str.decode???
.. method:: str.decode([encoding[, errors]])
Decodes the string using the codec registered for *encoding*. *encoding*
......@@ -737,6 +743,24 @@ string functions based on regular expressions.
found.
.. method:: str.format(format_string, *args, **ksargs)
Perform a string formatting operation. The *format_string* argument can
contain literal text or replacement fields delimited by braces ``{}``. Each
replacement field contains either the numeric index of a positional argument,
or the name of a keyword argument. Returns a copy of *format_string* where
each replacement field is replaced with the string value of the corresponding
argument.
>>> "The sum of 1 + 2 is {0}".format(1+2)
'The sum of 1 + 2 is 3'
See :ref:`formatstrings` for a description of the various formatting options
that can be specified in format strings.
.. versionadded:: 3.0
.. method:: str.index(sub[, start[, end]])
Like :meth:`find`, but raise :exc:`ValueError` when the substring is not found.
......@@ -747,31 +771,23 @@ string functions based on regular expressions.
Return true if all characters in the string are alphanumeric and there is at
least one character, false otherwise.
For 8-bit strings, this method is locale-dependent.
.. method:: str.isalpha()
Return true if all characters in the string are alphabetic and there is at least
one character, false otherwise.
For 8-bit strings, this method is locale-dependent.
.. method:: str.isdigit()
Return true if all characters in the string are digits and there is at least one
character, false otherwise.
For 8-bit strings, this method is locale-dependent.
.. method:: str.isidentifier()
Return true if the string is a valid identifier according to the language
definition.
.. XXX link to the definition?
definition, section :ref:`identifiers`.
.. method:: str.islower()
......@@ -779,16 +795,12 @@ string functions based on regular expressions.
Return true if all cased characters in the string are lowercase and there is at
least one cased character, false otherwise.
For 8-bit strings, this method is locale-dependent.
.. method:: str.isspace()
Return true if there are only whitespace characters in the string and there is
at least one character, false otherwise.
For 8-bit strings, this method is locale-dependent.
.. method:: str.istitle()
......@@ -796,16 +808,12 @@ string functions based on regular expressions.
character, for example uppercase characters may only follow uncased characters
and lowercase characters only cased ones. Return false otherwise.
For 8-bit strings, this method is locale-dependent.
.. method:: str.isupper()
Return true if all cased characters in the string are uppercase and there is at
least one cased character, false otherwise.
For 8-bit strings, this method is locale-dependent.
.. method:: str.join(seq)
......@@ -827,8 +835,6 @@ string functions based on regular expressions.
Return a copy of the string converted to lowercase.
For 8-bit strings, this method is locale-dependent.
.. method:: str.lstrip([chars])
......@@ -984,41 +990,24 @@ string functions based on regular expressions.
Return a copy of the string with uppercase characters converted to lowercase and
vice versa.
For 8-bit strings, this method is locale-dependent.
.. method:: str.title()
Return a titlecased version of the string: words start with uppercase
characters, all remaining cased characters are lowercase.
For 8-bit strings, this method is locale-dependent.
.. method:: str.translate(table[, deletechars])
Return a copy of the string where all characters occurring in the optional
argument *deletechars* are removed, and the remaining characters have been
mapped through the given translation table, which must be a string of length
256.
.. method:: str.translate(map)
You can use the :func:`maketrans` helper function in the :mod:`string` module to
create a translation table. For string objects, set the *table* argument to
``None`` for translations that only delete characters::
Returns a copy of the *s* where all characters have been mapped through the
*map* which must be a mapping of Unicode ordinals (integers) to Unicode
ordinals, strings or ``None``. Unmapped characters are left
untouched. Characters mapped to ``None`` are deleted.
>>> 'read this short text'.translate(None, 'aeiou')
'rd ths shrt txt'
.. versionadded:: 2.6
Support for a ``None`` *table* argument.
.. note::
For Unicode objects, the :meth:`translate` method does not accept the optional
*deletechars* argument. Instead, it returns a copy of the *s* where all
characters have been mapped through the given translation table which must be a
mapping of Unicode ordinals to Unicode ordinals, Unicode strings or ``None``.
Unmapped characters are left untouched. Characters mapped to ``None`` are
deleted. Note, a more flexible approach is to create a custom character mapping
codec using the :mod:`codecs` module (see :mod:`encodings.cp1251` for an
A more flexible approach is to create a custom character mapping codec
using the :mod:`codecs` module (see :mod:`encodings.cp1251` for an
example).
......@@ -1026,8 +1015,6 @@ string functions based on regular expressions.
Return a copy of the string converted to uppercase.
For 8-bit strings, this method is locale-dependent.
.. method:: str.zfill(width)
......@@ -1037,10 +1024,10 @@ string functions based on regular expressions.
.. versionadded:: 2.2.2
.. _string-formatting:
.. _old-string-formatting:
String Formatting Operations
----------------------------
Old String Formatting Operations
--------------------------------
.. index::
single: formatting, string (%)
......@@ -1052,14 +1039,18 @@ String Formatting Operations
single: % formatting
single: % interpolation
String and Unicode objects have one unique built-in operation: the ``%``
operator (modulo). This is also known as the string *formatting* or
*interpolation* operator. Given ``format % values`` (where *format* is a string
or Unicode object), ``%`` conversion specifications in *format* are replaced
with zero or more elements of *values*. The effect is similar to the using
:cfunc:`sprintf` in the C language. If *format* is a Unicode object, or if any
of the objects being converted using the ``%s`` conversion are Unicode objects,
the result will also be a Unicode object.
.. XXX better?
.. note::
The formatting operations described here are obsolete and my go away in future
versions of Python. Use the new :ref:`string-formatting` in new code.
String objects have one unique built-in operation: the ``%`` operator (modulo).
This is also known as the string *formatting* or *interpolation* operator.
Given ``format % values`` (where *format* is a string), ``%`` conversion
specifications in *format* are replaced with zero or more elements of *values*.
The effect is similar to the using :cfunc:`sprintf` in the C language.
If *format* requires a single argument, *values* may be a single non-tuple
object. [#]_ Otherwise, *values* must be a tuple with exactly the number of
......@@ -1164,7 +1155,7 @@ The conversion types are:
| ``'r'`` | String (converts any python object using | \(5) |
| | :func:`repr`). | |
+------------+-----------------------------------------------------+-------+
| ``'s'`` | String (converts any python object using | \(6) |
| ``'s'`` | String (converts any python object using | |
| | :func:`str`). | |
+------------+-----------------------------------------------------+-------+
| ``'%'`` | No argument is converted, results in a ``'%'`` | |
......@@ -1203,9 +1194,6 @@ Notes:
The precision determines the maximal number of characters used.
(6)
If the object or format provided is a :class:`unicode` string, the resulting
string will also be :class:`unicode`.
The precision determines the maximal number of characters used.
......@@ -2019,6 +2007,7 @@ the particular object.
on all file-like objects.
.. XXX does this still apply?
.. attribute:: file.encoding
The encoding that this file uses. When Unicode strings are written to a file,
......
Doc/library/string.rst
View file @ 4b49131f
......@@ -8,15 +8,13 @@
.. index:: module: re
The :mod:`string` module contains a number of useful constants and
classes, as well as some deprecated legacy functions that are also
available as methods on strings. In addition, Python's built-in string
classes support the sequence type methods described in the
:ref:`typesseq` section, and also the string-specific methods described
in the :ref:`string-methods` section. To output formatted strings use
template strings or the ``%`` operator described in the
:ref:`string-formatting` section. Also, see the :mod:`re` module for
string functions based on regular expressions.
The :mod:`string` module contains a number of useful constants and classes, as
well as some deprecated legacy functions that are also available as methods on
strings. In addition, Python's built-in string classes support the sequence type
methods described in the :ref:`typesseq` section, and also the string-specific
methods described in the :ref:`string-methods` section. To output formatted
strings, see the :ref:`string-formatting` section. Also, see the :mod:`re`
module for string functions based on regular expressions.
String constants
......@@ -78,6 +76,354 @@ The constants defined in this module are:
vertical tab.
.. _string-formatting:
String Formatting
-----------------
Starting in Python 3.0, the built-in string class provides the ability to do
complex variable substitutions and value formatting via the :func:`format`
method described in :pep:`3101`. The :class:`Formatter` class in the
:mod:`string` module allows you to create and customize your own string
formatting behaviors using the same implementation as the built-in
:meth:`format` method.
.. class:: Formatter
The :class:`Formatter` class has the following public methods:
.. method:: format(format_string, *args, *kwargs)
:meth:`format` is the primary API method. It takes a format template
string, and an arbitrary set of positional and keyword argument.
:meth:`format` is just a wrapper that calls :meth:`vformat`.
.. method:: vformat(format_string, args, kwargs)
This function does the actual work of formatting. It is exposed as a
separate function for cases where you want to pass in a predefined
dictionary of arguments, rather than unpacking and repacking the
dictionary as individual arguments using the ``*args`` and ``**kwds``
syntax. :meth:`vformat` does the work of breaking up the format template
string into character data and replacement fields. It calls the various
methods described below.
In addition, the :class:`Formatter` defines a number of methods that are
intended to be replaced by subclasses:
.. method:: parse(format_string)
Loop over the format_string and return an iterable of tuples
(*literal_text*, *field_name*, *format_spec*, *conversion*). This is used
by :meth:`vformat` to break the string in to either literal text, or
replacement fields.
The values in the tuple conceptually represent a span of literal text
followed by a single replacement field. If there is no literal text
(which can happen if two replacement fields occur consecutively), then
*literal_text* will be a zero-length string. If there is no replacement
field, then the values of *field_name*, *format_spec* and *conversion*
will be ``None``.
.. method:: get_field(field_name, args, kwargs, used_args)
Given *field_name* as returned by :meth:`parse` (see above), convert it to
an object to be formatted. The default version takes strings of the form
defined in :pep:`3101`, such as "0[name]" or "label.title". It records
which args have been used in *used_args*. *args* and *kwargs* are as
passed in to :meth:`vformat`.
.. method:: get_value(key, args, kwargs)
Retrieve a given field value. The *key* argument will be either an
integer or a string. If it is an integer, it represents the index of the
positional argument in *args*; if it is a string, then it represents a
named argument in *kwargs*.
The *args* parameter is set to the list of positional arguments to
:meth:`vformat`, and the *kwargs* parameter is set to the dictionary of
keyword arguments.
For compound field names, these functions are only called for the first
component of the field name; Subsequent components are handled through
normal attribute and indexing operations.
So for example, the field expression '0.name' would cause
:meth:`get_value` to be called with a *key* argument of 0. The ``name``
attribute will be looked up after :meth:`get_value` returns by calling the
built-in :func:`getattr` function.
If the index or keyword refers to an item that does not exist, then an
:exc:`IndexError` or :exc:`KeyError` should be raised.
.. method:: check_unused_args(used_args, args, kwargs)
Implement checking for unused arguments if desired. The arguments to this
function is the set of all argument keys that were actually referred to in
the format string (integers for positional arguments, and strings for
named arguments), and a reference to the *args* and *kwargs* that was
passed to vformat. The set of unused args can be calculated from these
parameters. :meth:`check_unused_args` is assumed to throw an exception if
the check fails.
.. method:: format_field(value, format_spec)
:meth:`format_field` simply calls the global :func:`format` built-in. The
method is provided so that subclasses can override it.
.. method:: convert_field(value, conversion)
Converts the value (returned by :meth:`get_field`) given a conversion type
(as in the tuple returned by the :meth:`parse` method.) The default
version understands 'r' (repr) and 's' (str) conversion types.
.. versionadded:: 3.0
.. _formatstrings:
Format String Syntax
--------------------
The :meth:`str.format` method and the :class:`Formatter` class share the same
syntax for format strings (although in the case of :class:`Formatter`,
subclasses can define their own format string syntax.)
Format strings contain "replacement fields" surrounded by curly braces ``{}``.
Anything that is not contained in braces is considered literal text, which is
copied unchanged to the output. If you need to include a brace character in the
literal text, it can be escaped by doubling: ``{{`` and ``}}``.
The grammar for a replacement field is as follows:
.. productionlist:: sf
replacement_field: "{" `field_name` ["!" `conversion`] [":" `format_spec`] "}"
field_name: (`identifier` | `integer`) ("." `attribute_name` | "[" element_index "]")*
attribute_name: `identifier`
element_index: `integer`
conversion: "r" | "s"
format_spec: <described in the next section>
In less formal terms, the replacement field starts with a *field_name*, which
can either be a number (for a positional argument), or an identifier (for
keyword arguments). Following this is an optional *conversion* field, which is
preceded by an exclamation point ``'!'``, and a *format_spec*, which is preceded
by a colon ``':'``.
The *field_name* itself begins with either a number or a keyword. If it's a
number, it refers to a positional argument, and if it's a keyword it refers to a
named keyword argument. This can be followed by any number of index or
attribute expressions. An expression of the form ``'.name'`` selects the named
attribute using :func:`getattr`, while an expression of the form ``'[index]'``
does an index lookup using :func:`__getitem__`.
Some simple format string examples::
"First, thou shalt count to {0}" # References first positional argument
"My quest is {name}" # References keyword argument 'name'
"Weight in tons {0.weight}" # 'weight' attribute of first positional arg
"Units destroyed: {players[0]}" # First element of keyword argument 'players'.
The *conversion* field causes a type coercion before formatting. Normally, the
job of formatting a value is done by the :meth:`__format__` method of the value
itself. However, in some cases it is desirable to force a type to be formatted
as a string, overriding its own definition of formatting. By converting the
value to a string before calling :meth:`__format__`, the normal formatting logic
is bypassed.
Two conversion flags are currently supported: ``'!s'`` which calls :func:`str()`
on the value, and ``'!r'`` which calls :func:`repr()`.
Some examples::
"Harold's a clever {0!s}" # Calls str() on the argument first
"Bring out the holy {name!r}" # Calls repr() on the argument first
The *format_spec* field contains a specification of how the value should be
presented, including such details as field width, alignment, padding, decimal
precision and so on. Each value type can define it's own "formatting
mini-language" or interpretation of the *format_spec*.
Most built-in types support a common formatting mini-language, which is
described in the next section.
A *format_spec* field can also include nested replacement fields within it.
These nested replacement fields can contain only a field name; conversion flags
and format specifications are not allowed. The replacement fields within the
format_spec are substituted before the *format_spec* string is interpreted.
This allows the formatting of a value to be dynamically specified.
For example, suppose you wanted to have a replacement field whose field width is
determined by another variable::
"A man with two {0:{1}}".format("noses", 10)
This would first evaluate the inner replacement field, making the format string
effectively::
"A man with two {0:10}"
Then the outer replacement field would be evaluated, producing::
"noses "
Which is subsitituted into the string, yielding::
"A man with two noses "
(The extra space is because we specified a field width of 10, and because left
alignment is the default for strings.)
.. versionadded:: 3.0
.. _formatspec:
Format Specification Mini-Language
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
"Format specifications" are used within replacement fields contained within a
format string to define how individual values are presented (see
:ref:`formatstrings`.) They can also be passed directly to the builtin
:func:`format` function. Each formattable type may define how the format
specification is to be interpreted.
Most built-in types implement the following options for format specifications,
although some of the formatting options are only supported by the numeric types.
A general convention is that an empty format string (``""``) produces the same
result as if you had called :func:`str()` on the value.
The general form of a *standard format specifier* is:
.. productionlist:: sf
format_spec: [[`fill`]`align`][`sign`][0][`width`][.`precision`][`type`]
fill: <a character other than '}'>
align: "<" | ">" | "=" | "^"
sign: "+" | "-" | " "
width: `integer`
precision: `integer`
type: "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "x" | "X" | "%"
The *fill* character can be any character other than '}' (which signifies the
end of the field). The presence of a fill character is signaled by the *next*
character, which must be one of the alignment options. If the second character
of *format_spec* is not a valid alignment option, then it is assumed that both
the fill character and the alignment option are absent.
The meaning of the various alignment options is as follows:
+---------+----------------------------------------------------------+
| Option | Meaning |
+=========+==========================================================+
| ``'<'`` | Forces the field to be left-aligned within the available |
| | space (This is the default.) |
+---------+----------------------------------------------------------+
| ``'>'`` | Forces the field to be right-aligned within the |
| | available space. |
+---------+----------------------------------------------------------+
| ``'='`` | Forces the padding to be placed after the sign (if any) |
| | but before the digits. This is used for printing fields |
| | in the form '+000000120'. This alignment option is only |
| | valid for numeric types. |
+---------+----------------------------------------------------------+
| ``'^'`` | Forces the field to be centered within the available |
| | space. |
+---------+----------------------------------------------------------+
Note that unless a minimum field width is defined, the field width will always
be the same size as the data to fill it, so that the alignment option has no
meaning in this case.
The *sign* option is only valid for number types, and can be one of the
following:
+---------+----------------------------------------------------------+
| Option | Meaning |
+=========+==========================================================+
| ``'+'`` | indicates that a sign should be used for both |
| | positive as well as negative numbers. |
+---------+----------------------------------------------------------+
| ``'-'`` | indicates that a sign should be used only for negative |
| | numbers (this is the default behavior). |
+---------+----------------------------------------------------------+
| space | indicates that a leading space should be used on |
| | positive numbers, and a minus sign on negative numbers. |
+---------+----------------------------------------------------------+
*width* is a decimal integer defining the minimum field width. If not
specified, then the field width will be determined by the content.
If the *width* field is preceded by a zero (``'0'``) character, this enables
zero-padding. This is equivalent to an *alignment* type of ``'='`` and a *fill*
character of ``'0'``.
The *precision* is a decimal number indicating how many digits should be
displayed after the decimal point for a floating point value. For non-number
types the field indicates the maximum field size - in other words, how many
characters will be used from the field content. The *precision* is ignored for
integer values.
Finally, the *type* determines how the data should be presented.
The available integer presentation types are:
+---------+----------------------------------------------------------+
| Type | Meaning |
+=========+==========================================================+
| ``'b'`` | Binary. Outputs the number in base 2. |
+---------+----------------------------------------------------------+
| ``'c'`` | Character. Converts the integer to the corresponding |
| | unicode character before printing. |
+---------+----------------------------------------------------------+
| ``'d'`` | Decimal Integer. Outputs the number in base 10. |
+---------+----------------------------------------------------------+
| ``'o'`` | Octal format. Outputs the number in base 8. |
+---------+----------------------------------------------------------+
| ``'x'`` | Hex format. Outputs the number in base 16, using lower- |
| | case letters for the digits above 9. |
+---------+----------------------------------------------------------+
| ``'X'`` | Hex format. Outputs the number in base 16, using upper- |
| | case letters for the digits above 9. |
+---------+----------------------------------------------------------+
| None | the same as ``'d'`` |
+---------+----------------------------------------------------------+
The available presentation types for floating point and decimal values are:
+---------+----------------------------------------------------------+
| Type | Meaning |
+=========+==========================================================+
| ``'e'`` | Exponent notation. Prints the number in scientific |
| | notation using the letter 'e' to indicate the exponent. |
+---------+----------------------------------------------------------+
| ``'E'`` | Exponent notation. Same as ``'e'`` except it uses an |
| | upper case 'E' as the separator character. |
+---------+----------------------------------------------------------+
| ``'f'`` | Fixed point. Displays the number as a fixed-point |
| | number. |
+---------+----------------------------------------------------------+
| ``'F'`` | Fixed point. Same as ``'f'``. |
+---------+----------------------------------------------------------+
| ``'g'`` | General format. This prints the number as a fixed-point |
| | number, unless the number is too large, in which case |
| | it switches to ``'e'`` exponent notation. |
+---------+----------------------------------------------------------+
| ``'G'`` | General format. Same as ``'g'`` except switches to |
| | ``'E'`` if the number gets to large. |
+---------+----------------------------------------------------------+
| ``'n'`` | Number. This is the same as ``'g'``, except that it uses |
| | the current locale setting to insert the appropriate |
| | number separator characters. |
+---------+----------------------------------------------------------+
| ``'%'`` | Percentage. Multiplies the number by 100 and displays |
| | in fixed (``'f'``) format, followed by a percent sign. |
+---------+----------------------------------------------------------+
| None | similar to ``'g'``, except that it prints at least one |
| | digit after the decimal point. |
+---------+----------------------------------------------------------+
.. _template-strings:
Template strings
----------------
......@@ -208,6 +554,7 @@ They are not available as string methods.
leading and trailing whitespace.
.. XXX is obsolete with unicode.translate
.. function:: maketrans(from, to)
Return a translation table suitable for passing to :func:`translate`, that will
......@@ -219,250 +566,3 @@ They are not available as string methods.
Don't use strings derived from :const:`lowercase` and :const:`uppercase` as
arguments; in some locales, these don't have the same length. For case
conversions, always use :func:`lower` and :func:`upper`.
Deprecated string functions
---------------------------
The following list of functions are also defined as methods of string and
Unicode objects; see section :ref:`string-methods` for more information on
those. You should consider these functions as deprecated, although they will
not be removed until Python 3.0. The functions defined in this module are:
.. function:: atof(s)
.. deprecated:: 2.0
Use the :func:`float` built-in function.
.. index:: builtin: float
Convert a string to a floating point number. The string must have the standard
syntax for a floating point literal in Python, optionally preceded by a sign
(``+`` or ``-``). Note that this behaves identical to the built-in function
:func:`float` when passed a string.
.. note::
.. index::
single: NaN
single: Infinity
When passing in a string, values for NaN and Infinity may be returned, depending
on the underlying C library. The specific set of strings accepted which cause
these values to be returned depends entirely on the C library and is known to
vary.
.. function:: atoi(s[, base])
.. deprecated:: 2.0
Use the :func:`int` built-in function.
.. index:: builtin: eval
Convert string *s* to an integer in the given *base*. The string must consist
of one or more digits, optionally preceded by a sign (``+`` or ``-``). The
*base* defaults to 10. If it is 0, a default base is chosen depending on the
leading characters of the string (after stripping the sign): ``0x`` or ``0X``
means 16, ``0`` means 8, anything else means 10. If *base* is 16, a leading
``0x`` or ``0X`` is always accepted, though not required. This behaves
identically to the built-in function :func:`int` when passed a string. (Also
note: for a more flexible interpretation of numeric literals, use the built-in
function :func:`eval`.)
.. function:: atol(s[, base])
.. deprecated:: 2.0
Use the :func:`long` built-in function.
.. index:: builtin: long
Convert string *s* to a long integer in the given *base*. The string must
consist of one or more digits, optionally preceded by a sign (``+`` or ``-``).
The *base* argument has the same meaning as for :func:`atoi`. A trailing ``l``
or ``L`` is not allowed, except if the base is 0. Note that when invoked
without *base* or with *base* set to 10, this behaves identical to the built-in
function :func:`long` when passed a string.
.. function:: capitalize(word)
Return a copy of *word* with only its first character capitalized.
.. function:: expandtabs(s[, tabsize])
Expand tabs in a string replacing them by one or more spaces, depending on the
current column and the given tab size. The column number is reset to zero after
each newline occurring in the string. This doesn't understand other non-printing
characters or escape sequences. The tab size defaults to 8.
.. function:: find(s, sub[, start[,end]])
Return the lowest index in *s* where the substring *sub* is found such that
*sub* is wholly contained in ``s[start:end]``. Return ``-1`` on failure.
Defaults for *start* and *end* and interpretation of negative values is the same
as for slices.
.. function:: rfind(s, sub[, start[, end]])
Like :func:`find` but find the highest index.
.. function:: index(s, sub[, start[, end]])
Like :func:`find` but raise :exc:`ValueError` when the substring is not found.
.. function:: rindex(s, sub[, start[, end]])
Like :func:`rfind` but raise :exc:`ValueError` when the substring is not found.
.. function:: count(s, sub[, start[, end]])
Return the number of (non-overlapping) occurrences of substring *sub* in string
``s[start:end]``. Defaults for *start* and *end* and interpretation of negative
values are the same as for slices.
.. function:: lower(s)
Return a copy of *s*, but with upper case letters converted to lower case.
.. function:: split(s[, sep[, maxsplit]])
Return a list of the words of the string *s*. If the optional second argument
*sep* is absent or ``None``, the words are separated by arbitrary strings of
whitespace characters (space, tab, newline, return, formfeed). If the second
argument *sep* is present and not ``None``, it specifies a string to be used as
the word separator. The returned list will then have one more item than the
number of non-overlapping occurrences of the separator in the string. The
optional third argument *maxsplit* defaults to 0. If it is nonzero, at most
*maxsplit* number of splits occur, and the remainder of the string is returned
as the final element of the list (thus, the list will have at most
``maxsplit+1`` elements).
The behavior of split on an empty string depends on the value of *sep*. If *sep*
is not specified, or specified as ``None``, the result will be an empty list.
If *sep* is specified as any string, the result will be a list containing one
element which is an empty string.
.. function:: rsplit(s[, sep[, maxsplit]])
Return a list of the words of the string *s*, scanning *s* from the end. To all
intents and purposes, the resulting list of words is the same as returned by
:func:`split`, except when the optional third argument *maxsplit* is explicitly
specified and nonzero. When *maxsplit* is nonzero, at most *maxsplit* number of
splits -- the *rightmost* ones -- occur, and the remainder of the string is
returned as the first element of the list (thus, the list will have at most
``maxsplit+1`` elements).
.. versionadded:: 2.4
.. function:: splitfields(s[, sep[, maxsplit]])
This function behaves identically to :func:`split`. (In the past, :func:`split`
was only used with one argument, while :func:`splitfields` was only used with
two arguments.)
.. function:: join(words[, sep])
Concatenate a list or tuple of words with intervening occurrences of *sep*.
The default value for *sep* is a single space character. It is always true that
``string.join(string.split(s, sep), sep)`` equals *s*.
.. function:: joinfields(words[, sep])
This function behaves identically to :func:`join`. (In the past, :func:`join`
was only used with one argument, while :func:`joinfields` was only used with two
arguments.) Note that there is no :meth:`joinfields` method on string objects;
use the :meth:`join` method instead.
.. function:: lstrip(s[, chars])
Return a copy of the string with leading characters removed. If *chars* is
omitted or ``None``, whitespace characters are removed. If given and not
``None``, *chars* must be a string; the characters in the string will be
stripped from the beginning of the string this method is called on.
.. versionchanged:: 2.2.3
The *chars* parameter was added. The *chars* parameter cannot be passed in
earlier 2.2 versions.
.. function:: rstrip(s[, chars])
Return a copy of the string with trailing characters removed. If *chars* is
omitted or ``None``, whitespace characters are removed. If given and not
``None``, *chars* must be a string; the characters in the string will be
stripped from the end of the string this method is called on.
.. versionchanged:: 2.2.3
The *chars* parameter was added. The *chars* parameter cannot be passed in
earlier 2.2 versions.
.. function:: strip(s[, chars])
Return a copy of the string with leading and trailing characters removed. If
*chars* is omitted or ``None``, whitespace characters are removed. If given and
not ``None``, *chars* must be a string; the characters in the string will be
stripped from the both ends of the string this method is called on.
.. versionchanged:: 2.2.3
The *chars* parameter was added. The *chars* parameter cannot be passed in
earlier 2.2 versions.
.. function:: swapcase(s)
Return a copy of *s*, but with lower case letters converted to upper case and
vice versa.
.. function:: translate(s, table[, deletechars])
Delete all characters from *s* that are in *deletechars* (if present), and then
translate the characters using *table*, which must be a 256-character string
giving the translation for each character value, indexed by its ordinal. If
*table* is ``None``, then only the character deletion step is performed.
.. function:: upper(s)
Return a copy of *s*, but with lower case letters converted to upper case.
.. function:: ljust(s, width)
rjust(s, width)
center(s, width)
These functions respectively left-justify, right-justify and center a string in
a field of given width. They return a string that is at least *width*
characters wide, created by padding the string *s* with spaces until the given
width on the right, left or both sides. The string is never truncated.
.. function:: zfill(s, width)
Pad a numeric string on the left with zero digits until the given width is
reached. Strings starting with a sign are handled correctly.
.. function:: replace(str, old, new[, maxreplace])
Return a copy of string *str* with all occurrences of substring *old* replaced
by *new*. If the optional argument *maxreplace* is given, the first
*maxreplace* occurrences are replaced.
Doc/library/strings.rst
View file @ 4b49131f
......@@ -8,12 +8,11 @@ String Services
The modules described in this chapter provide a wide range of string
manipulation operations.
In addition, Python's built-in string classes support the sequence type
methods described in the :ref:`typesseq` section, and also the
string-specific methods described in the :ref:`string-methods` section.
To output formatted strings use template strings or the ``%`` operator
described in the :ref:`string-formatting` section. Also, see the
:mod:`re` module for string functions based on regular expressions.
In addition, Python's built-in string classes support the sequence type methods
described in the :ref:`typesseq` section, and also the string-specific methods
described in the :ref:`string-methods` section. To output formatted strings,
see the :ref:`string-formatting` section. Also, see the :mod:`re` module for
string functions based on regular expressions.
.. toctree::
......
Doc/reference/datamodel.rst
View file @ 4b49131f
......@@ -1279,15 +1279,36 @@ Basic customization
.. index::
builtin: str
statement: print
builtin: print
Called by the :func:`str` built-in function and by the :keyword:`print`
statement to compute the "informal" string representation of an object. This
Called by the :func:`str` built-in function and by the :func:`print`
function to compute the "informal" string representation of an object. This
differs from :meth:`__repr__` in that it does not have to be a valid Python
expression: a more convenient or concise representation may be used instead.
The return value must be a string object.
.. method:: object.__format__(self, format_spec)
.. index::
pair: string; conversion
builtin: str
builtin: print
Called by the :func:`format` built-in function (and by extension, the
:meth:`format` method of class :class:`str`) to produce a "formatted"
string representation of an object. The ``format_spec`` argument is
a string that contains a description of the formatting options desired.
The interpretation of the ``format_spec`` argument is up to the type
implementing :meth:`__format__`, however most classes will either
delegate formatting to one of the built-in types, or use a similar
formatting option syntax.
See :ref:`formatspec` for a description of the standard formatting syntax.
The return value must be a string object.
.. method:: object.__lt__(self, other)
object.__le__(self, other)
object.__eq__(self, other)
......
Doc/reference/expressions.rst
View file @ 4b49131f
......@@ -5,12 +5,10 @@
Expressions
***********
.. index:: single: expression
.. index:: expression, BNF
This chapter explains the meaning of the elements of expressions in Python.
.. index:: single: BNF
**Syntax Notes:** In this and the following chapters, extended BNF notation will
be used to describe syntax, not lexical analysis. When (one alternative of) a
syntax rule has the form
......@@ -18,8 +16,6 @@ syntax rule has the form
.. productionlist:: *
name: `othername`
.. index:: single: syntax
and no semantics are given, the semantics of this form of ``name`` are the same
as for ``othername``.
......@@ -852,9 +848,9 @@ 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
also overloaded by string and unicode objects to perform string formatting (also
also overloaded by string objects to perform string formatting (also
known as interpolation). The syntax for string formatting is described in the
Python Library Reference, section :ref:`string-formatting`.
Python Library Reference, section :ref:`old-string-formatting`.
The floor division operator, the modulo operator, and the :func:`divmod`
function are not defined for complex numbers. Instead, convert to a
......@@ -985,9 +981,12 @@ Comparison of objects of the same type depends on the type:
* Numbers are compared arithmetically.
* Bytes objects are compared lexicographically using the numeric values of
their elements.
* Strings are compared lexicographically using the numeric equivalents (the
result of the built-in function :func:`ord`) of their characters. Unicode and
8-bit strings are fully interoperable in this behavior. [#]_
result of the built-in function :func:`ord`) of their characters. [#]_
String and bytes object can't be compared!
* Tuples and lists are compared lexicographically using comparison of
corresponding elements. This means that to compare equal, each element must
......@@ -1020,11 +1019,10 @@ particular, dictionaries support membership testing as a nicer way of spelling
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.
For the Unicode and string types, ``x in y`` is true if and only if *x* is a
substring of *y*. An equivalent test is ``y.find(x) != -1``. Note, *x* and *y*
need not be the same type; consequently, ``u'ab' in 'abc'`` will return
``True``. Empty strings are always considered to be a substring of any other
string, so ``"" in "abc"`` will return ``True``.
For the string and bytes types, ``x in y`` is true if and only if *x* is a
substring of *y*. An equivalent test is ``y.find(x) != -1``. Empty strings are
always considered to be a substring of any other string, so ``"" in "abc"`` will
return ``True``.
.. versionchanged:: 2.3
Previously, *x* was required to be a string of length ``1``.
......@@ -1272,7 +1270,7 @@ groups from right to left).
cases, Python returns the latter result, in order to preserve that
``divmod(x,y)[0] * y + x % y`` be very close to ``x``.
.. [#] While comparisons between unicode strings make sense at the byte
.. [#] While comparisons between strings make sense at the byte
level, they may be counter-intuitive to users. For example, the
strings ``u"\u00C7"`` and ``u"\u0327\u0043"`` compare differently,
even though they both represent the same unicode character (LATIN
......
Doc/tutorial/introduction.rst
View file @ 4b49131f
......@@ -399,8 +399,8 @@ The built-in function :func:`len` returns the length of a string::
basic transformations and searching.
:ref:`string-formatting`
The formatting operations invoked when strings are the
left operand of the ``%`` operator are described in more detail here.
The formatting operations invoked by the :meth:`format` string method are
described in more detail here.
.. _tut-unicodestrings:
......
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