FAQ: Recursion: Python - No Nested Lists Anymore, I Want Them to Turn Flat


This community-built FAQ covers the “No Nested Lists Anymore, I Want Them to Turn Flat” exercise from the lesson “Recursion: Python”.

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Hi, can anyone help here? what I understood so far (after learning Python for 2 months) is that we dont have to explicitly write “else” for an else statement, as long as we indent it on the same level as the if statment that should work. However, in the codes below, not using “else” has resulted of a different output…not sure why…

#this one is the model answer with “else”
def flatten(my_list):
result =
for el in my_list:
if isinstance(el, list):
print(“list found!”)
flat_list = flatten(el)
result += flat_list
return result

output -
[‘mercury’, ‘venus’, ‘earth’, ‘mars’, ‘jupiter’, ‘saturn’, ‘uranus’, ‘neptune’, ‘pluto’]

this one does not have else but instead "result.append(item) is indented on the same level as the if statement.

def flatten(my_list):
result =
for item in my_list:
if isinstance(item, list):
print(“list found!”)
flat_list = flatten(item)
result += flat_list
return result

output - [‘mercury’, ‘venus’, ‘earth’, [‘earth’], ‘mars’, ‘jupiter’, ‘saturn’, [‘jupiter’, ‘saturn’], [[‘jupiter’, ‘saturn’]], ‘uranus’, ‘neptune’, ‘pluto’, [‘neptune’, ‘pluto’]]