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Python Python Collections (Retired) Lists Redux Manipulating Lists

travis ueki
travis ueki
2,102 Points
Posted by travis ueki
travis ueki
2,102 Points

Can't figure out the data type of lists in order to result in my for loop removing the nested list

In the last elif I want to check the condition of (psuedo code)

for item in list: elif item == list: the_list.remove(item)

lists.py 
the_list = ["a", 2, 3, 1, False, [1, 2, 3]]

# Your code goes below here
the_list = ["a", 2, 3, 1, False, [1, 2, 3]]

# Your code goes below here
newItem = the_list.pop(3)
the_list.insert(0, newItem)

def cleanUp(list):
  for item in list:
    if item == 'a':
      list.remove('a')
      print(list)
      continue
    elif item == False:
      list.remove(item)
      print(the_list)
      continue
    elif item == type(list):
      list.remove(item)
      print(list)
      continue


cleanUp(the_list)

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,426 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,426 Points

The statement you are looking for is isinstance(item, list) to check if item is of type list. There are two issues with this approach.

  1. You are using the key word list as your argument name for cleanUp which overwrites the namespace andlist is no longer the type but instead has the value of the argument passed to cleanUp. It is not a good idea to use list or any keyword as a variable name. Is is common to you "lst" for a list variable.

  2. You are operating on the same list you are looping over. What happens is the list is shortened by the remove actions then the loop thinks it's done since the length is less and doesn't loop over the last item.

also, since all the code covered by an if or elif, the continue statements aren't needed:

newItem = the_list.pop(3)
the_list.insert(0, newItem)

def cleanUp(mylist):
  for idx, item in enumerate(mylist[:]):
    if item == 'a':
      mylist.remove('a')
    elif item == False:
      mylist.remove(item)
    elif isinstance(item, list):
      mylist.remove(list(item))

cleanUp(the_list)

The last item can also be removed using the_list.pop() which removes the last item in the list:

the_list.remove('a')
the_list.remove(False)
the_list.pop()