# Python中map函数

python中的map()函数

map(function, iterable, ...)

1.对可迭代函数'iterable'中的每一个元素应用‘function’方法，将结果作为list返回。

```>> def add100(x):
...     return x+100
...
>>> hh = [11,22,33]
[111, 122, 133]```

如果是python 3见上一篇博客。

2、如果给出了额外的可迭代参数，则对每个可迭代参数中的元素‘并行’的应用‘function’。（翻译的不好，这里的关键是‘并行’）

```>>> def abc(a, b, c):
...     return a*10000 + b*100 + c
...
>>> list1 = [11,22,33]
>>> list2 = [44,55,66]
>>> list3 = [77,88,99]
>>> map(abc,list1,list2,list3)
[114477, 225588, 336699]```

3、如果'function'给出的是‘None’，自动假定一个‘identity’函数（这个‘identity’不知道怎么解释，看例子吧）

```>>> list1 = [11,22,33]
>>> map(None,list1)
[11, 22, 33]
>>> list1 = [11,22,33]
>>> list2 = [44,55,66]
>>> list3 = [77,88,99]
>>> map(None,list1,list2,list3)
[(11, 44, 77), (22, 55, 88), (33, 66, 99)]```

```map(f, iterable)

[f(x) for x in iterable]```

```>>> def add100(x):
...     return x + 100
...
>>> list1 = [11,22,33]
[101, 102, 103]

>>> [add100(i) for i in list1]
[101, 102, 103]```

```>>> def abc(a, b, c):
...     return a*10000 + b*100 + c
...
>>> list1 = [11,22,33]
>>> list2 = [44,55,66]
>>> list3 = [77,88,99]
>>> map(abc,list1,list2,list3)
[114477, 225588, 336699]```

`[abc(a,b,c) for a in list1 for b in list2 for c in list3]`

`[114477, 114488, 114499, 115577, 115588, 115599, 116677, 116688, 116699, 224477, 224488, 224499, 225577, 225588, 225599, 226677, 226688, 226699, 334477, 334488, 334499, 335577, 335588, 335599, 336677, 336688, 336699]`

```result = []

for a in list1:
for b in list2:
for c in list3:
result.append(abc(abc))```

11

22

33

44

55

66

77

88

99

map()只做了列上面的运算，而列表推导（也就是嵌套for循环）做了笛卡尔乘积

588 篇文章70 人订阅

0 条评论