笔记-python-字符串格式化-format()

笔记-python-字符串格式化-format()

1.      简介

本文介绍了python 字符串格式化方法format()的常规使用方式。

2.      使用

2.1.    Accessing arguments by position:

>>> '{0}, {1}, {2}'.format('a', 'b', 'c')

'a, b, c'

>>> '{}, {}, {}'.format('a', 'b', 'c')  # 3.1+ 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'

2.2.    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'

2.3.    Accessing arguments’ attributes:

>>> c = 3-5j

>>> ('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:

...     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)'

2.4.    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"

2.5.    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'

2.6.    Using the comma as a thousands separator:

>>> '{:,}'.format(1234567890)

'1,234,567,890'

2.7.    Expressing a percentage:

>>> points = 19

>>> total = 22

>>> 'Correct answers: {:.2%}'.format(points/total)

'Correct answers: 86.36%'

2.8.    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'

2.9.    Nesting arguments and more complex examples:

>>> for align, text in zip('<^>', ['left', 'center', 'right']):

...     '{0:{fill}{align}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), end=' ')

...     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