Unexpected behavior with list.append
I worked with my interpreter to figure out the behavior of the Python method append()
and found:
In [335]: b = [].append(1)
In [336]: b
In [337]:
In [337]: b = [].append('1')
In [338]: b
Which puzzles me, because I thought that whenever we call append()
in a list, we add new objects to the end, so it should not be called append()
on an empty list (like what I did above) the same result that I could achieve with:
In [339]: b=[]
In [340]: b.append(1)
In [341]: b
Out[341]: [1]
I may have a misconception here, so please correct me if I am wrong.
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Which puzzles me because I thought that whenever we call
append()
on the list, we add new objects to the end
It is right. But you're forgetting that append()
(like most methods that mutate objects) it always returns None
in Python because it works in place. So, doing this:
b = [].append(1)
matches:
b = None
1
technically added to a list []
, but there is no way to access that list after the call append()
, as it is b
assigned to the return value of the method call.
The second example works great simply because you don't reassign b
and thereby lose the reference to the list object.
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