python学习笔记——列表推导 list comprehension

python 的列表推导的方式进行遍历，这样可以利用python 的特性加快遍历效率

>>> numbers = range(10)>>> size = len(numbers)>>> evens = []>>> i = 0>>> while i < size:...     if i % 2 == 0:...             evens.append(i)...     i += 1... >>> evens[0, 2, 4, 6, 8]>>> [i for i in range(10) if i % 2 == 0][0, 2, 4, 6, 8]>>> 

列表推导还可以代替嵌套循环

>>> for i in [1,2,3]:...     for j in [1,2,3]:...             z = i*j...             print z... 123246369>>> print [i*j for i in [1,2,3] for j in [1,2,3]][1, 2, 3, 2, 4, 6, 3, 6, 9]>>> print i*j for i in [1,2,3] for j in [1,2,3]  File "<stdin>", line 1    print i*j for i in [1,2,3] for j in [1,2,3]                ^SyntaxError: invalid syntax