CODEWITHSUNDEEP
pythonlisttypeerror
Jayyyyyy
Jayyyyyy

Reputation: 197

I don't understand the error message 'NoneType' object is not iterable in python

def make_list_of_lists(n):
    the_list = []
    sublist = []
    for i in range(n):
        print(sublist)
        the_list.extend(sublist)
        sublist = sublist.insert(len(sublist), i+1)
    return the_list

I got a error message of this function, which is:

'NoneType' object is not iterable'

I don't understand why this happen?

Upvotes: 0

Views: 115

Answers (4)

Chris
Chris

Reputation: 4391

As noted in other answers, it is the sublist = sublist.insert(len(sublist), i+1) line that causes the problem.

However, you seem to be wanting to make a list of lists (based on the function name), which your code currently does not do.

def make_list_of_lists(n):
      the_list = []
      sublist = []
      for i in range(n):
          the_list.append(sublist)
      return the_list

print(make_list_of_lists(5))

This prints an empty list of 5 empty lists:

[[], [], [], [], []]

Upvotes: 0

user9386531
user9386531

Reputation: 

sublist = sublist.insert(len(sublist), i+1)

This makes sublist to be none. That is the problem.

Upvotes: 0

azro
azro

Reputation: 54148

The insert operation modifying the object inplace, and like a almost all of these kind of method it returns None because you don't need the return value. After 1 iteration it tried to do the following which requires to iterate over None to add all of its elements, and you can't

the_list.extend(None)

So just do

sublist.insert(len(sublist), i + 1)

Upvotes: 1

ingvar
ingvar

Reputation: 4377

Look at this line:

sublist = sublist.insert(len(sublist), i+1)

insert function does insert in place and returns None, so on next iteration here

the_list.extend(sublist)

sublist is None while extend function requires iterable parameter. Fixed code:

def make_list_of_lists(n):
    the_list = []
    sublist = []
    for i in range(n):
        print(sublist)
        the_list.extend(sublist)
        sublist.insert(len(sublist), i + 1)
    return the_list

make_list_of_lists(3)

[]

[1]

[1, 2]

[1, 1, 2]

Upvotes: 4

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