Home/ Questions/Ways to resolve the error - valueerror: list.remove(x): x not in list
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Nolan Li
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Asked: 2022-05-18T15:59:19+00:00 In:

Ways to resolve the error – valueerror: list.remove(x): x not in list

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For the problem “valueerror: list.remove(x): x not in list.” I tried to fix it, but It doesn’t work and returns the result I want. Here is my program:

def manage_collide(bolts, aliens):
  # Check if a bolt collides with any alien(s)
  for b in bolts:
  for a in aliens:
  if b['rect'].colliderect(a['rect']):
  for a in aliens:
  a['health'] -= 1
  bolts.remove(b)
  if a['health'] == 0:
  aliens.remove(a)
  # Return bolts, aliens dictionaries
  return bolts, aliens

and

ValueError: list.remove(x): x not in list

has occurred. I’ve checked the entire command line but still can’t find the mistake.

valueerror
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2 Answers

  1. Best Answer
    Expert

    The cause: Because when you use remove, you must name the removed item by name rather than index, this error “value error: x is not in list” will display when the code is run.

    Solution: You are unable to utilize a list.remove, so you should use del list[x] to delete items. It’s OK to use del because we’re deleting items by their index. Using del, the code will work appropriately regardless of the item’s name.
    To find out for sure, consult the following code:

    aliens = [[4,3,2,1],[4,3,2,1],[4,3,2,1]]
print(aliens)
bolts = [b for b in range(1,30)]
for b in bolts:
del aliens[0][0]
print(aliens)
if len(aliens[0]) == 0:
del aliens[0]
if len(aliens) == 0
print("you win")
break

     

    • 0

  2. This is due to a bug in the code. This is how your code looks simplified: 

    for b in bolts:
 for a in aliens:
 for a in aliens:
 bolts.remove(b)

    This is why aliens loops over aliens multiple time for each entry in b. This will cause aliens to loop over aliens multiple times for every entry in b.

    There are a few things you need to fix. To use a instead of aliens, first change the inner loop. 

    for b in bolts:
 for a in aliens:
 for c in aliens:
 if hit:
 bolts.remove(b)

    Second, remove b only once. so: 

    for b in bolts:
 for a in aliens:
 should_remove = False
 for c in aliens:
 if hit:
 should_remove = True
 if should_remove:
 bolts.remove(b)

    This code has other problems, but it is what is causing your problem. Martijn’s post might also be of assistance.

    • 8

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