格式化字符串

>>> a,b=5,42
>>> print(a,b)
5 42
>>> 'this is {}, and that is {}'.format(a,b)
'this is 5, and that is 42'
>>> s = 'this is {}, and that is {}'
>>> s
'this is {}, and that is {}'
>>> s.format(a, b)
'this is 5, and that is 42'
>>> id(s)
64800544
>>> new = s.format(a,b)
>>> id(new)
64454464
>>> 'this is {1}, and that is {0}'.format(a,b)
'this is 42, and that is 5'
>>> 'this is {bob} and that is {fred}'.format(bob=a, fred=b)
'this is 5 and that is 42'
>>> d = dict(bob=a,fred=b)
>>> 'this is {bob} and that is {fred}'.format(**d)
'this is 5 and that is 42'
>>>