I wanted to remove a substring from a string, for example "a" in "a,b,c" and then return "b,c" to me, it does not matter what's the order of a in string(like "a,b,c", "b,a,c", and so one).
DELIMITER = ","
def remove(member, members_string):
"""removes target from string"""
members = members_string.split(DELIMITER)
members.remove(member)
return DELIMITER.join(members)
print remove("a","b,a,c")
output: b,c
The above function is working as it is expected.
My question is that accidently I modified my code, and it looks as:
def remove_2(member, members_string):
"""removes target from string"""
members = members_string.split(DELIMITER).remove(member)
return DELIMITER.join(members)
You can see that I modified
members = members_string.split(DELIMITER)
members.remove(member)
to
members = members_string.split(DELIMITER).remove(member)
after that the method is broken, it throws
Traceback (most recent call last):
File "test.py", line 15, in <module>
remove_2("a","b,a,c")
File "test.py", line 11, in remove_2
return DELIMITER.join(members)
TypeError
Based on my understanding, members_string.split(DELIMITER) is a list, and invokes remove() is allowed and it should return the new list and stores into members, but
when I print members_string.split(DELIMITER) it returns None, it explains why throws TypeError, my question is , why it returns None other than a list with elements "b" and "c"?
remove() does not return anything. It modifies the list it's called on (lists are mutable, so it would be a major waste of cpu time and memory to create a new list) so returning the same list would be somewhat pointless.