Python error:
attributeerror: ‘nonetype’ object has no attribute ‘append’

a=[]
b=[1,2,3,4]
a = a.append(b)

After one execution, the type of a changes to nonetype
the above errors will appear in the next execution.

This is because append modifies a itself and returns none. The return value cannot be reassigned to a.

terms of settlement:

Change the variable name:
C =]
b = [1,2,3,4]
C = A. append (b)
problem solving.

Or
change a = a.append (b) to a.append (b)