Python高级语法

列表推导式

[ expression for x in X [if condition]
             for y in Y [if condition]
             ...
             for n in N [if condition] ]

例如：

>>> [(x, y) for x in range(5) if x % 2 == 0 for y in range(5) if y % 2 == 1]
[(0, 1), (0, 3), (2, 1), (2, 3), (4, 1), (4, 3)]

等价于：

>>> L = []
>>> for x in range(5):
...     if x % 2 == 0:
...         for y in range(5):
...             if y % 2 == 1:
...                 L.append((x, y))
>>> L
[(0, 1), (0, 3), (2, 1), (2, 3), (4, 1), (4, 3)]

with ... as

with open('/path/to/file', 'r') as f:
    print(f.read())

文件使用完毕必须关闭资源，一般使用try ... finally，而with ... as自动调用了f.close()，代码更加简洁。

Python高级语法

推荐阅读