Python基础教程——5条件、循环和其他语句

简单的例子

>>> [x*x for x in range(10)]

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

>>> [x*x for x in range(10) if x % 3 == 0]

[0, 9, 36, 81]

>>> [(x,y) for x in range(3) for y in range(3)]

[(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2), (2, 0), (2, 1), (2, 2)]

复杂些的例子——找出首字母相同的男孩和女孩

>>> girls = ['alice','bernice','clarice']

>>> boys = ['chris','arnold','bob']

>>> [b+'+'+g for b in boys for g in girls if b[0] == g[0]]

['chris+clarice', 'arnold+alice', 'bob+bernice']

效率更高的实现

>>> girls = ['alice','bernice','clarice']

>>> boys = ['chris','arnold','bob']

>>> letterGirls = {}

>>> for girl in girls:

letterGirls.setdefault(girl[0],[]).append(girl)

>>> print [b + '+' + g for b in boys for g in letterGirls[b[0]]]

['chris+clarice', 'arnold+alice', 'bob+bernice']

>>> letterGirls

{'a': ['alice'], 'c': ['clarice'], 'b': ['bernice']}

摘自《Python基础教程》