#9139: Add examples for str.format().

This commit is contained in:
Ezio Melotti 2010-07-02 22:17:29 +00:00
parent 68f59415b6
commit e11690ab34
1 changed files with 152 additions and 23 deletions

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@ -201,7 +201,7 @@ string formatting behaviors using the same implementation as the built-in
.. 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
(as in the tuple returned by the :meth:`parse` method). The default
version understands 'r' (repr) and 's' (str) conversion types.
@ -238,6 +238,8 @@ The *field_name* is optionally followed by a *conversion* field, which is
preceded by an exclamation point ``'!'``, and a *format_spec*, which is preceded
by a colon ``':'``. These specify a non-default format for the replacement value.
See also the :ref:`formatspec` section.
The *field_name* itself begins with an *arg_name* that is either 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. If the numerical arg_names in a format string
@ -248,6 +250,10 @@ 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__`.
.. versionchanged:: 2.7
The positional argument specifiers can be omitted, so ``'{} {}'`` is
equivalent to ``'{0} {1}'``.
Some simple format string examples::
"First, thou shalt count to {0}" # References first positional argument
@ -286,26 +292,7 @@ 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 substituted 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.)
See the :ref:`formatexamples` section for some examples.
.. _formatspec:
@ -315,7 +302,7 @@ 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 built-in
:ref:`formatstrings`). They can also be passed directly to the built-in
:func:`format` function. Each formattable type may define how the format
specification is to be interpreted.
@ -349,7 +336,7 @@ 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.) |
| | space (this is the default). |
+---------+----------------------------------------------------------+
| ``'>'`` | Forces the field to be right-aligned within the |
| | available space. |
@ -505,6 +492,148 @@ The available presentation types for floating point and decimal values are:
+---------+----------------------------------------------------------+
.. _formatexamples:
Format examples
^^^^^^^^^^^^^^^
This section contains examples of the new format syntax and comparison with
the old ``%``-formatting.
In most of the cases the syntax is similar to the old ``%``-formatting, with the
addition of the ``{}`` and with ``:`` used instead of ``%``.
For example, ``'%03.2f'`` can be translated to ``'{:03.2f}'``.
The new format syntax also supports new and different options, shown in the
follow examples.
Accessing arguments by position::
>>> '{0}, {1}, {2}'.format('a', 'b', 'c')
'a, b, c'
>>> '{}, {}, {}'.format('a', 'b', 'c') # 2.7+ only
'a, b, c'
>>> '{2}, {1}, {0}'.format('a', 'b', 'c')
'c, b, a'
>>> '{2}, {1}, {0}'.format(*'abc') # unpacking argument sequence
'c, b, a'
>>> '{0}{1}{0}'.format('abra', 'cad') # arguments' indices can be repeated
'abracadabra'
Accessing arguments by name::
>>> 'Coordinates: {latitude}, {longitude}'.format(latitude='37.24N', longitude='-115.81W')
'Coordinates: 37.24N, -115.81W'
>>> coord = {'latitude': '37.24N', 'longitude': '-115.81W'}
>>> 'Coordinates: {latitude}, {longitude}'.format(**coord)
'Coordinates: 37.24N, -115.81W'
Accessing arguments' attributes::
>>> ('The complex number {0} is formed from the real part {0.real} '
... 'and the imaginary part {0.imag}.').format(c)
'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0.'
>>> class Point(object):
... def __init__(self, x, y):
... self.x, self.y = x, y
... def __str__(self):
... return 'Point({self.x}, {self.y})'.format(self=self)
...
>>> str(Point(4, 2))
'Point(4, 2)'
Accessing arguments' items::
>>> coord = (3, 5)
>>> 'X: {0[0]}; Y: {0[1]}'.format(coord)
'X: 3; Y: 5'
Replacing ``%s`` and ``%r``::
>>> "repr() shows quotes: {!r}; str() doesn't: {!s}".format('test1', 'test2')
"repr() shows quotes: 'test1'; str() doesn't: test2"
Aligning the text and specifying a width::
>>> '{:<30}'.format('left aligned')
'left aligned '
>>> '{:>30}'.format('right aligned')
' right aligned'
>>> '{:^30}'.format('centered')
' centered '
>>> '{:*^30}'.format('centered') # use '*' as a fill char
'***********centered***********'
Replacing ``%+f``, ``%-f``, and ``% f`` and specifying a sign::
>>> '{:+f}; {:+f}'.format(3.14, -3.14) # show it always
'+3.140000; -3.140000'
>>> '{: f}; {: f}'.format(3.14, -3.14) # show a space for positive numbers
' 3.140000; -3.140000'
>>> '{:-f}; {:-f}'.format(3.14, -3.14) # show only the minus -- same as '{:f}; {:f}'
'3.140000; -3.140000'
Replacing ``%x`` and ``%o`` and converting the value to different bases::
>>> # format also supports binary numbers
>>> "int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}".format(42)
'int: 42; hex: 2a; oct: 52; bin: 101010'
>>> # with 0x, 0o, or 0b as prefix:
>>> "int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}".format(42)
'int: 42; hex: 0x2a; oct: 0o52; bin: 0b101010'
Using the comma as a thousands separator::
>>> '{:,}'.format(1234567890)
'1,234,567,890'
Expressing a percentage::
>>> points = 19.5
>>> total = 22
>>> 'Correct answers: {:.2%}.'.format(points/total)
'Correct answers: 88.64%'
Using type-specific formatting::
>>> import datetime
>>> d = datetime.datetime(2010, 7, 4, 12, 15, 58)
>>> '{:%Y-%m-%d %H:%M:%S}'.format(d)
'2010-07-04 12:15:58'
Nesting arguments and more complex examples::
>>> for align, text in zip('<^>', ['left', 'center', 'right']):
... '{0:{align}{fill}16}'.format(text, fill=align, align=align)
...
'left<<<<<<<<<<<<'
'^^^^^center^^^^^'
'>>>>>>>>>>>right'
>>>
>>> octets = [192, 168, 0, 1]
>>> '{:02X}{:02X}{:02X}{:02X}'.format(*octets)
'C0A80001'
>>> int(_, 16)
3232235521
>>>
>>> width = 5
>>> for num in range(5,12):
... for base in 'dXob':
... print '{0:{width}{base}}'.format(num, base=base, width=width),
... print
...
5 5 5 101
6 6 6 110
7 7 7 111
8 8 10 1000
9 9 11 1001
10 A 12 1010
11 B 13 1011
Template strings
----------------