04python 中的各种推导式（python函数）

列表推导式与生成器表达式

print([i for i in range(10)])        # 列表推导式

g = (i for i in range(10))           # 生成器表达式
print(g)                             # 打印的结果为生成器   

print([i for i in g])                # 再次调用列表解析

>>>[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
<generator object <genexpr> at 0x0000006E50CBED58>
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

 列表推导式的补充：加上条件

ret = [i for i in range(30) if i % 3 == 0]
print(ret)

>>>[0, 3, 6, 9, 12, 15, 18, 21, 24, 27]

 多重嵌套

>>> names = [['Tom', 'Billy', 'Jefferson', 'Andrew', 'Wesley', 'Steven', 'Joe'],
['Alice', 'Jill', 'Ana', 'Wendy', 'Jennifer', 'Sherry', 'Eva']]
>>> print([name for lst in names for name in lst if name.count('e') >= 2])
['Jefferson', 'Wesley', 'Steven', 'Jennifer']

 字典推导式

>>> dic = {'k1': 'v1', 'k2': 'v2', 'k3': 'v3'}
>>> {v1: k1 for k1, v1 in dic.items()}
{'v1': 'k1', 'v2': 'k2', 'v3': 'k3'}

 字典推导式值得注意的地方

>>> {key:value for key in "ABC" for value in range(1,10)}
{'A': 9, 'B': 9, 'C': 9}

  元组推导式

自带去重功能

squared = {x**2 for x in [1, -1, 2]}
print(squared)
# Output: set([1, 4])

>>>(1, 4)