>>> [name.upper() for name in names if len(name)>3]
['ALICE', 'JERRY', 'WENDY', 'SMITH']
例2: 求(x,y)其中x是0-5之间的偶数，y是0-5之间的奇数组成的元祖列表
复制代码 代码如下:
>>> [(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)]
例3: 求M中3,6,9组成的列表
复制代码 代码如下:
>>> M = [[1,2,3],
... [4,5,6],
... [7,8,9]]
>>> M
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
>>> [row[2] for row in M]
[3, 6, 9]
#或者用下面的方式
>>> [M[row][2] for row in (0,1,2)]
[3, 6, 9]
例4: 求M中斜线1,5,9组成的列表
复制代码 代码如下:
>>> M
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
>>> [M[i][i] for i in range(len(M))]
[1, 5, 9]
例5: 求M,N中矩阵和元素的乘积
复制代码 代码如下:
>>> M = [[1,2,3],
... [4,5,6],
... [7,8,9]]
>>> N = [[2,2,2],
... [3,3,3],
... [4,4,4]]
>>> [M[row][col]*N[row][col] for row in range(3) for col in range(3)]
[2, 4, 6, 12, 15, 18, 28, 32, 36]
>>> [[M[row][col]*N[row][col] for col in range(3)] for row in range(3)]
[[2, 4, 6], [12, 15, 18], [28, 32, 36]]
>>> [[M[row][col]*N[row][col] for row in range(3)] for col in range(3)]
[[2, 12, 28], [4, 15, 32], [6, 18, 36]]
例5: 讲字典中age键，按照条件赋新值
复制代码 代码如下:
>>> bob
{'pay': 3000, 'job': 'dev', 'age': 42, 'name': 'Bob Smith'}
>>> sue
{'pay': 4000, 'job': 'hdw', 'age': 45, 'name': 'Sue Jones'}
>>> people = [bob, sue]
>>> [rec['age']+100 if rec['age'] >= 45 else rec['age'] for rec in people] # 注意for位置
[42, 145]
【字典推导式】
字典和集合推导式是该思想的延续，语法差不多，只不过产生的是集合和字典而已。其基本格式如下:
复制代码 代码如下:
{ key_expr: value_expr for value in collection if condition }
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