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Python Python Collections (Retired) Slices Deleting Or Replacing Slices

Posted by Abdillah Hasny
Abdillah Hasny
Courses Plus Student 3,886 Points

Why i can't remove all char with this loop

import string
my_list = [1,2,3,'a','b','d',5,'f','h']
alphabet = list(string.ascii_lowercase)

for item in my_list:
    if item in alphabet:
        while True:
            try:
                my_list.remove(item)
            except:
                break

print(my_list)

what is wrong in my code , i still get char inside my_list after removing them in the loop who have any char inside

[1, 2, 3, 'b', 5, 'h'] b and h still in the list

1 Answer

Gunhoo Yoon
Gunhoo Yoon
5,027 Points
Gunhoo Yoon
Gunhoo Yoon
5,027 Points

I think that's happening because list is keep mutating on the fly.

Let's say your algorithm reached 'a' at index 3.

'a' is removed since it's lowercase char and 'b' takes index 3 since list is mutable.

The loop points to next index which is 4.

'b' is not at index 4 anymore it is 'd'

Same thing happen for 'f' and 'h'

Try this I haven't tested it yet but it will work.

import string
my_list = [1,2,3,'a','b','d',5,'f','h']

#made copy of list. Actual copy that doesn't share any reference.
#I originally did copied_list  = my_list then found out they are treated like object.
copied_list = my_list[:]

alphabet = list(string.ascii_lowercase)

for item in copied_list:
    if item in alphabet:
        while True:
            try:
                my_list.remove(item)
            except:
                break

print(my_list)

#What i mean by my mistake up there.
a = [1, 2, 3]
b = a
c = a[:]

a.append(4)

print(a, b) #[1,2,3,4] [1,2,3,4]
print(c) #[1,2,3]
Abdillah Hasny
Abdillah Hasny
Courses Plus Student 3,886 Points

i get the idea .. thanks Gunhoo Yoon