这个表达式在Python中是正确的：{} .keys（）。insert（0，“”）== None。 为什么？

Question

Look to my Python session:

>>> {}.keys().insert(0, "") == None
True

but:

>>> k = {}.keys()
>>> k
[]
>>> k.insert(0, "")
>>> k
['']

Why??

PS . Thanks for help! Python have very strange design - do not support chaining:

• http://en.wikipedia.org/wiki/Method_chaining

That is root of my problem...

Answer 1

list.insert returns None ; when you print k you're printing the new state of the list.

Answer 2

You are checking the return type to None in case 1 which would evaluate to True . Python insert returns None