python中%和format
两者都是格式化字符串用的,前者是比较老的版本,现在已经不推荐,后者更强大一些
%
In [22]: print '%s' % 'hello world' hello world In [23]: print '%s: %d' % ('name', 13) name: 13 In [24]: import math In [25]: print 'PI: %.5f' % pi --------------------------------------------------------------------------- NameError Traceback (most recent call last) <ipython-input-25-b457c33a3305> in <module>() ----> 1 print 'PI: %.5f' % pi NameError: name 'pi' is not defined In [26]: print 'PI: %.5f' % math.pi PI: 3.14159 In [27]: a = ('Bill', 'Gates') In [28]: '%s, %s' % a Out[28]: 'Bill, Gates'
format
Help on method_descriptor: format(...) S.format(*args, **kwargs) -> string Return a formatted version of S, using substitutions from args and kwargs. The substitutions are identified by braces ('{' and '}'). (END)
用法如下:
In [29]: "{}".format('hello') Out[29]: 'hello' In [30]: '{} {}'.format('hello', 'world') Out[30]: 'hello world' In [31]: '{1} {0} {0}'.format('hello', 'python') Out[31]: 'python hello hello' In [32]: '{0} {0} {1}'.format(*('hello', 'Python')) Out[32]: 'hello hello Python' In [33]: '{length} {width}'.format(length=12, width=13) Out[33]: '12 13' In [34]: '{length} {width}'.format(width=12, length=13) Out[34]: '13 12' In [35]: '{length} {width}'.format({'width': 12, 'length': 13}) --------------------------------------------------------------------------- KeyError Traceback (most recent call last) <ipython-input-35-f8990d240643> in <module>() ----> 1 '{length} {width}'.format({'width': 12, 'length': 13}) KeyError: 'length' In [36]: '{length} {width}'.format(**{'width': 12, 'length': 13}) Out[36]: '13 12' In [37]: "'x': {0[0]}, 'y': {0[1]}".format((12, 13)) Out[37]: "'x': 12, 'y': 13"
最常用的可能就是上面这些,不过format不仅仅如此,还可以做前分位符,指定字符串宽度,代替%s %r,处理时间的格式等
>>> "repr() shows quotes: {!r}; str() doesn't: {!s}".format('test1', 'test2') "repr() shows quotes: 'test1'; str() doesn't: test2" >>> '{:<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***********' >>> '{:+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' >>> # 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' >>> '{:,}'.format(1234567890) '1,234,567,890' >>> points = 19.5 >>> total = 22 >>> 'Correct answers: {:.2%}'.format(points/total) 'Correct answers: 88.64%' >>> 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'
大家可以看看官方文档(以上部分例子摘自官方文档):
https://docs.python.org/2/library/string.html
注意:大括号和变量名之间是不能有空格的,否则会提示错误keyerror,如下
In [1]: print '{name}'.format(name='wang') wang In [2]: print '{ name }'.format(name='wang') --------------------------------------------------------------------------- KeyError Traceback (most recent call last) <ipython-input-2-7b45246725e0> in <module>() ----> 1 print '{ name }'.format(name='wang') KeyError: ' name ' In [3]: print '{ name }'.format(name='wang')