Appending turns my list to NoneType

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'nonetype' object has no attribute 'append'
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attributeerror: 'list' object has no attribute 'append

In Python Shell, I entered:

aList = ['a', 'b', 'c', 'd']  
for i in aList:  
    print(i)

and got

a  
b  
c  
d  

but when I tried:

aList = ['a', 'b', 'c', 'd']  
aList = aList.append('e')  
for i in aList:  
    print(i) 

and got

Traceback (most recent call last):  
  File "<pyshell#22>", line 1, in <module>  
    for i in aList:  
TypeError: 'NoneType' object is not iterable  

Does anyone know what's going on? How can I fix/get around it?

list.append is a method that modifies the existing list. It doesn't return a new list -- it returns None, like most methods that modify the list. Simply do aList.append('e') and your list will get the element appended.

Appending turns my list to NoneType, In the loop, the iterator used by the for loop looks at lst[0] , and you'd move 3 to the end of the list by appending and removing. Now the list looks  Instead of agesList=agesList.append(age) use only agesList.append(age). Because list.append() returns None and overrides your list. Thus the first iteration of your for-loop will run fine, after that agesList is None and you will get the error you're mentioning.

Generally, what you want is the accepted answer. But if you want the behavior of overriding the value and creating a new list (which is reasonable in some cases^), what you could do instead is use the "splat operator", also known as list unpacking:

aList = [*aList, 'e']
#: ['a', 'b', 'c', 'd', 'e']

Or, if you need to support python 2, use the + operator:

aList = aList + ['e']
#: ['a', 'b', 'c', 'd', 'e']

^ There are many cases where you want to avoid the side effects of mutating with .append(). For one, imagine you want to append something to a list you've taken as a function argument. Whoever is using the function probably doesn't expect that the list they provided is going to be changed. Using something like this keeps your function "pure" without "side effects".

why is my list Nonetype? in python, 18/18 AttributeError: 'NoneType' object has no attribute 'append' To get elements you need to iterate inside the list which is already located inside an list. Other programming languages might call this a void function or a procedure. What we tried to do was: l = ['one', 'two', 'three'] print(l.append('four')) And to our (initial) surprise, got: None. Instead we should have called the method first (updating the list, l) and then called print(l) to see the updated list.

Delete your second line aList = aList.append('e') and use only aList.append("e"), this should get rid of that problem.

18/18 AttributeError: 'NoneType' object has no attribute 'append , Appending turns my list to NoneType. 1 View. 0 Traceback (most recent call last): File " ", line 1, in for i in aList: TypeError: 'NoneType' object is not iterable. It means that the data variable is passing None (which is type NoneType), its equivalent for nothing. So it can’t be iterable as a list, as you are trying to do. You’re calling write_file with arguments like this: write_file (foo, bar) But you haven’t defined ‘foo’ correctly, or you have a typo in your code so that it’s creating a

Appending turns my list to NoneType, Instead we should have called the method first (updating the list, l) and then called print(l) to see the updated list. type(l.append("four") # NoneType In fact​, it turned out from some googling that Python functions have a  python,list,sorting,null. If you want the None and '' values to appear last, you can have your key function return a tuple, so the list is sorted by the natural order of that tuple. The tuple has the form (is_none, is_empty, value); this way, the tuple for a None value will be

Why do Python functions return None?, append returns None , as is idiomatic in Python for a mutating function. You should be modifying the list before calling the function if that is your intention. The original list is : [1, None, 4, None, None, 5, 8, None] List after removal of None values : [1, 4, 5, 8] Method #3 : Using filter() filter function is the most concise and readable way to perform this particular task.

Python - empty Lists getting initialized as noneType?, Solved: Hi there, I'm trying to do something extremely simple. I have a list and want to append a variable to it (in the middle of a for loop). i = CC List: 13 users ( show ) amulhern anaconda-maint-list blivet-maint-list jkonecny jonathan kellin mkolman rvykydal sbueno vanmeeuwen+fedora vponcova vtrefny wwoods

Comments
  • And since it doesn't return anything, you're setting aList to None if you do do the assignment, which is why you're getting the error.
  • All functions return something :)
  • true - but sometimes that something is None. But is None really something? My head hurts!
  • @kindall: "doesn't return anything" should be "in effect, it's the same is if the method doesn't have a return statement and returns None implicitly". And. "Methods which mutate an object almost never return a value, pop is the notable exception."