Python->列表解析式

'''Python中的列表解析式,格式如下：
[expression for expr1 in sequence1
for expr2 in sequence2
for exprN in sequenceN
if condition]'''

选择长度大于3，并将字母全部转成大写

>>> names=['Bob','Tom','alice','Wendy','Smith']
>>> [name.upper() for name in names if len(name)>3]
['ALICE', 'WENDY', 'SMITH']

求(x,y)组合,x为0-5之间偶数;y为0-5之间奇数

>>> [(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)]

获取矩阵列数列

>>> M=[[1,2,3],
...    [4,5,6],
...    [7,8,9]]
>>> [row[2] for row in M]
[3, 6, 9]
>>> [M[i][i] for i in range(len(M))]
[1, 5, 9]
>>> [M[j][-j-1] for j in range(len(M))]
[3, 5, 7]