Python3执行程序，为什么返回None? [英] Python3 exec, why returns None?

问题描述

当代码在此文本下方时，并返回结果None为什么?

When the code below this text, and returns the result None why?

with open('exx.py', 'rb') as file:
ff = compile(file.read(), 'exx.py', 'exec')
snip_run = exec(ff, locals())
if 'result' in locals():
    print(snip_run, result)
else:
    print(snip_run)

结果:

777777
None

模块代码exx.py:

Module code exx.py:

print('777777')

推荐答案

当然，问题不仅在于 print 返回 None ，还在于exec总是返回None .

The problem of course is not only that print returns None, it is that exec returns None, always.

>>> exec('42') is None
True

如果需要返回值，请使用 eval :

If you'd need the return value, you'd use eval:

>>> eval('42')
42

之后，您会注意到 print 仍返回 None ...

after which you'd notice that print still returns None...

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