List append() in for loop [duplicate]

Question

This question already has answers here:

Why does list.append evaluate to false in a boolean context? [duplicate] (7 answers)

Closed 3 years ago.

In Python, trying to do the most basic append function to a list with a loop: Not sure what i am missing here:

a=[]
for i in range(5):    
    a=a.append(i)
a

returns: 'NoneType' object has no attribute 'append'

Answer 1

You don't need the assignment, list.append(x) will always append x to a and therefore there's no need te redefine a.

a = []
for i in range(5):    
    a.append(i)
print(a)

is all you need. This works because lists are mutable.

Also see the docs on data structures.

Answer 2

No need to re-assign.

a=[]
for i in range(5):    
    a.append(i)
a

Answer 3

The list.append function does not return any value(but None), it just add the value to the list you are using to call that method.

In the first loop round you will assign None (because the no-return of append) to a, then in the second round it will try to call a.append, as a is None it will raise the Exception you are seeing

You just need to change it to:

a=[]
for i in range(5):    
    a.append(i)
a # the list with the new items.

Edit: As Juan said in comments it does return something, None