打印在地图中时不打印，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)

它不打印任何东西.这是为什么?我试过了

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

sys.stdout.write(x)

也是，但也不起作用.

推荐答案

由于 lambda x: print(x) 是 Python 中的语法错误3，我假设 Python 3.这意味着 map 返回一个生成器，这意味着要让 map 实际调用列表的每个元素上的函数，您需要遍历生成的生成器.

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，如果你愿意，你也可以去掉 lambda:

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

list(map(print,primes))

但是，在这一点上，您最好让 print 处理它:

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

print(*primes, sep='
')

<小时>

注意:我之前说过 ' '.join 是个好主意.这仅适用于 str 列表.

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

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