Python Forum

Hi,

I'm trying to learn Python by myself, and while trying some code to learn more about lists I tried something that didn't output what I did except to... Can you help me and furthermore explain me the reason why it didn't work.

empty_list = []
first_var = 1

filled_list = empty_list.append(first_var)
print(filled_list)

It prints me out "None" instead of [1]…

Thanks a lot

The append method doesn't return anything (or rather it returns None), it modifies the list you appended to. You want to print empty_list.

This is an important thing about lists: they can be changed in place. You'll note that string can't, which is why most of the string methods return a new string.

Okay! If I've understood It's like if I wrote:

filled_list = None

Because it doesn't take in count the append() method to print it out ?

Thank you very much :)

Well, it does take into account the append method. That's where the None came from. It's just that the actual appending is done to empty_list. That is, after line 4, empty_list is [1] and filled_list is None.

empty_list = []
first_var = 1

filled_list = empty_list.append(first_var) # here it will append to empty_list and append returns None which is assigned to filled_list
print(filled_list)
print(empty_list)

Output:
None
[1]
>>>

So your code is equivalent to

empty_list = []
first_var = 1
empty_list.append(first_var)
filled_list = None
print(filled_list)

Okay, it's clearer to me now ! Thanks you both for helping newbies like me we appreciate that :D see you soon ^^'