> For the complete documentation index, see [llms.txt](https://eastlakeside.gitbook.io/interpy-zh/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eastlakeside.gitbook.io/interpy-zh/map_n_filter/map.md).

# Map

`Map` 会将一个函数映射到一个输入列表的所有元素上。这是它的规范：

**规范**

```python
map(function_to_apply, list_of_inputs)
```

大多数时候，我们要把列表中所有元素一个个地传递给一个函数，并收集输出。比方说：

```python
items = [1, 2, 3, 4, 5]
squared = []
for i in items:
    squared.append(i**2)
```

`Map` 可以让我们用一种简单而漂亮得多的方式来实现。就是这样：

```python
items = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x**2, items))
```

大多数时候，我们使用匿名函数（lambdas）来配合 `map`, 所以我在上面也是这么做的。 不仅用于一列表的输入， 我们甚至可以用于一列表的函数！

```python
def multiply(x):
        return (x*x)
def add(x):
        return (x+x)

funcs = [multiply, add]
for i in range(5):
    value = map(lambda x: x(i), funcs)
    print(list(value))
    # 译者注：上面print时，加了list转换，是为了python2/3的兼容性
    #        在python2中map直接返回列表，但在python3中返回迭代器
    #        因此为了兼容python3, 需要list转换一下

# Output:
# [0, 0]
# [1, 2]
# [4, 4]
# [9, 6]
# [16, 8]
```


---

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