Python - Why does extend() and append() return Non

问题:

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Closed 7 years ago.

Possible Duplicate:
why does python's list.append evaluate to false?

In my opinion, I think list1.extend(list2) and list1.append(num) should return the mutated list rather than None (void). As well as having the side effect of destructively mutating the original list.

回答1:

I believe the intent was to promote readable code and reduce bugs. This decision was made a very long time ago, but you can probably find more by looking at the archives of the python/python-dev mailing lists.

Python3 would have been the opportunity to change this behaviour, but as you see it remains, so is not considered a design mistake by the development team