Changing of stored list value

Question

Hi can someone please explain to me why this function isn't working as I intended it to? I know I can do it by using the index of the list to check if the element is equal to a variable but why can't this method work?

Expectations- I wanted this function to change the element in list (stored) if it matches a particular value. IE chance letter c to the # symbol in this example.

Results - The list (stored) that is printed will have no difference and end up print [a,b,c,d,e]

Code

stored = ["a", "b", "c", "d", "e"]
def if_match():
  for letters in stored:
    if letters == "c":
      letters = "#"
  print stored

This isn’t valid python. Are you actually capitalizing the keywords `def`, `if` and `for`? — Joel Cornett, Apr 23 '18 at 02:22
Sorry its because i typed the code on my phone. How do i post it in code format? — Yeo Bryan, Apr 23 '18 at 02:25

score 0 · Answer 1 · 2018-04-23T02:50:43.423

0

It doesn't work because letters is a variable used just to iterate over the list. To actually change the value you need to do:

for x in range(len(stored)):
    if stored[x] == "c":
        stored[x] = "#"

Or you can enumerate through the list like this:

for index, value in enumerate(stored):
    if value == "c":
        stored[index] = "#"

This will actually change the value of "c" to "#".

edited Apr 23 '18 at 02:50

answered Apr 23 '18 at 02:34

Doesnt letters refer to each variable in the list ? So when that particular variable is equal to what i am checking it against i change the value of the variable? – Yeo Bryan Apr 23 '18 at 02:39
@YeoBryan it changes the value of the variable, but not the value present in the list – Apr 23 '18 at 02:42
@YeoBryan please accept my answer if it helped you – Apr 23 '18 at 02:49
It is not a copy. – juanpa.arrivillaga Apr 23 '18 at 02:50
@juanpa.arrivillaga can you please provide clarification as to why – Apr 23 '18 at 02:50
Because it is not a copy. Put some mutable object in a list, iterate over the list, mutate the object, and you will see it is not a copy – juanpa.arrivillaga Apr 23 '18 at 02:54
The keys point: assignment never mutates – juanpa.arrivillaga Apr 23 '18 at 02:55
@juanpa.arrivillaga so why doesn't changing the value of the variable letters change the value inside the list – Apr 23 '18 at 02:55
Because *assignment never mutates* – juanpa.arrivillaga Apr 23 '18 at 02:58
stored = [ "a","b","c","d","e"] n=0 for i in range(5): if stored[n] == "c": stored[n] = "#" n+=1 else: n+=1 print stored But for this code it works? Sorry but i am not rly sure why thats the case – Yeo Bryan Apr 23 '18 at 03:03
@YeoBryan Use proper formatting for your comment. I don't realy understand what you mean. Also, if this works, make sure you accept it – Apr 23 '18 at 03:11

Changing of stored list value

1 Answers1