在地图中打印时不打印，Python [英] Print doesn't print when it's in map, Python

问题描述

primes = [2,3,5,7..] (prime numbers)
map(lambda x:print(x),primes)

它不打印任何内容. 这是为什么? 我已经尝试过

It does not print anything. Why is that? I've tried

sys.stdout.write(x)

也可以，但是也不起作用.

too, but doesn't work either.

推荐答案

由于lambda x: print(x)是Python中的语法错误< 3，我假设使用Python3.这意味着map返回一个生成器，这意味着要获取map以便在列表的每个元素上实际调用该函数，您需要迭代生成的生成器.

Since lambda x: print(x) is a syntax error in Python < 3, I'm assuming Python 3. That means map returns a generator, meaning to get map to actually call the function on every element of a list, you need to iterate through the resultant generator.

幸运的是，这很容易做到:

Fortunately, this can be done easily:

list(map(lambda x:print(x),primes))

哦，如果愿意，您也可以摆脱lambda:

Oh, and you can get rid of the lambda too, if you like:

list(map(print,primes))

但是，此时最好让打印处理它:

But, at that point you are better off with letting print handle it:

print(*primes, sep='\n')

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注意:我之前说过'\n'.join是个好主意.这仅适用于str的列表.

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NOTE: I said earlier that '\n'.join would be a good idea. That is only true for a list of str's.

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