地图无法在python 3中按预期方式工作 [英] map doesn't work as expected in python 3

问题描述

新手在这里.

此代码在python 2.7中有效，但在3.3中无效

This code worked in python 2.7, but does not in 3.3

def extractFromZipFiles(zipFiles, files, toPath):
    extractFunction = lambda fileName:zipFiles.extract(fileName, toPath) 
    map (extractFunction,files)
    return

没有错误，但未提取文件.但是，当我用for循环替换时，效果很好.

No error but the files are not extracted. However when I replace with for loop works fine.

def extractFromZipFiles(zipFiles, files, toPath):
    for fn in files:
        zipFiles.extract(fn, toPath)
#     extractFunction = lambda fileName:zipFiles.extract(fileName, toPath) 
#     map (extractFunction,files)
    return

代码没有错误.

推荐答案

通常不鼓励使用map来调用函数，但是，不起作用的原因是因为Python 3返回了一个生成器，而不是列表，因此在您对其进行迭代之前，不会调用该函数.为了确保它调用这些函数，请执行以下操作:

It is generally discouraged to use map to call functions, but that being said, the reason it doesn't work is because Python 3 returns a generator, not a list, so the function isn't called until you've iterated on it. To ensure that it calls the functions:

list(map(extractFunction,files))

但是它正在创建一个未使用的列表.更好的方法是更明确:

But it's creating an unused list. The better approach is to be more explicit:

for file in files:
    extractFunction(file)

就像有头的情况一样，两行确实可以胜过一行.

As is the case with heads, two lines can indeed be better than one.

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