Map

python3.6

map(func, *iterables) --> map object<br><br>Make an iterator that computes the function using arguments from<br>each of the iterables.  Stops when the shortest iterable is exhausted.<br><br><br>

map(func, *iterables) --> map object

• func is a lambda anonymous function with simple logic. Complex logic needs to be designed by yourself;
• *iterables Iterable objects
• The result obtained by the map function is also an iterable object, but it can only be iterated once.

Example: Custom function simulates the built-in function map, the list increases and decreases by 1 and squares

The built-in function map implements the list's automatic increase and decrease by 1 and square

li = [1, 2, 3, 4, 5, 6, 7, 8, 9<span style="color: #000000">]
</span><span style="color: #008000">#</span><span style="color: #008000"> 自增1</span>
<span style="color: #0000ff">print</span>(list(map(<span style="color: #0000ff">lambda</span> x: x + 1<span style="color: #000000">, li)))
</span><span style="color: #008000">#</span><span style="color: #008000"> 自减1</span>
<span style="color: #0000ff">print</span>(list(map(<span style="color: #0000ff">lambda</span> x: x - 1<span style="color: #000000">, li)))
</span><span style="color: #008000">#</span><span style="color: #008000"> 平方</span>
<span style="color: #0000ff">print</span><span style="color: #000000">(
    list(
        map(</span><span style="color: #0000ff">lambda</span> x: x ** 2<span style="color: #000000">, li)
    )
)</span>

Custom function implementation

li = [1, 2, 3, 4, 5, 6, 7, 8, 9<span style="color: #000000">]


</span><span style="color: #008000">#</span><span style="color: #008000"> 自增1</span>
<span style="color: #0000ff">def</span><span style="color: #000000"> add1(x):
    </span><span style="color: #0000ff">return</span> x + 1


<span style="color: #008000">#</span><span style="color: #008000"> 自减1</span>
<span style="color: #0000ff">def</span><span style="color: #000000"> red1(x):
    </span><span style="color: #0000ff">return</span> x - 1


<span style="color: #008000">#</span><span style="color: #008000"> 平方</span>
<span style="color: #0000ff">def</span><span style="color: #000000"> square(x):
    </span><span style="color: #0000ff">return</span> x ** 2


<span style="color: #0000ff">def</span><span style="color: #000000"> map_test(func, l):
    tl </span>=<span style="color: #000000"> []
    </span><span style="color: #0000ff">for</span> i <span style="color: #0000ff">in</span><span style="color: #000000"> l:
        tl.append(func(i))
    </span><span style="color: #0000ff">return</span><span style="color: #000000"> tl

</span><span style="color: #008000">#</span><span style="color: #008000"> 调用上面定义的函数</span>
<span style="color: #0000ff">print</span><span style="color: #000000">(map_test(add1, li))
</span><span style="color: #0000ff">print</span><span style="color: #000000">(map_test(red1, li))
</span><span style="color: #0000ff">print</span>(map_test(square, li))

Custom function + anonymous function implementation

li = [1, 2, 3, 4, 5, 6, 7, 8, 9<span style="color: #000000">]

</span><span style="color: #0000ff">def</span><span style="color: #000000"> map_test(func, l):
    tl </span>=<span style="color: #000000"> []
    </span><span style="color: #0000ff">for</span> i <span style="color: #0000ff">in</span><span style="color: #000000"> l:
        tl.append(func(i))
    </span><span style="color: #0000ff">return</span><span style="color: #000000"> tl

</span><span style="color: #0000ff">print</span>(map_test(<span style="color: #0000ff">lambda</span> x: x + 1<span style="color: #000000">, li))
</span><span style="color: #0000ff">print</span>(map_test(<span style="color: #0000ff">lambda</span> x: x - 1<span style="color: #000000">, li))
</span><span style="color: #0000ff">print</span>(map_test(<span style="color: #0000ff">lambda</span> x: x ** 2, li))

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