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I am getting an error message that says

AttributeError: 'NoneType' object has no attribute 'something'
How can I understand this message?
What general scenarios might cause such an AttributeError, and how can I identify the problem?
This is a special case of AttributeErrors. It merits separate treatment because there are a lot of ways to get an unexpected None value from the code, so it's typically a different problem; for other AttributeErrors, the problem might just as easily be the attribute name.
See also What is a None value? and What is a 'NoneType' object? for an understanding of None and its type, NoneType.
                TODO: find a proper canonical for the general case of AttributeError, to include in the see-also section. stackoverflow.com/questions/11685936 is not suitable, because it was caused by a typo (mixed tab/space indentation) that has 2.x-specific effects, which causes confusion and inaccuracy in the answers.
– Karl Knechtel
                Mar 26 at 5:21
                Remembering to actually return from a function call is also helpful... trying to reference an item that wasn't returned doesn't usually work too well. Silly me.
– Shrout1
                Oct 27, 2022 at 18:06
You have a variable that is equal to None and you're attempting to access an attribute of it called 'something'.
foo = None
foo.something = 1
foo = None
print(foo.something)
Both will yield an AttributeError: 'NoneType'
                This is probably unhelpful until you point out how people might end up getting a None out of something. An explicit foo = None is unlikely to be the problem; it's going to be foo = something() and you don't realize something() might return None when it doesn't succeed or the result set was empty or whatever.
– tripleee
                Feb 4, 2019 at 8:02
                This is totally correct. For instance when you are using Django to develop an e-commerce application, you have worked on functionality of the cart and everything seems working when you test the cart functionality with a product. Then in the backend you delete the product been registered to the cart. If you attempt to go to the cart page again you will experience the error above. Proper fix must be handled to avoid this.
– Adeolu Temitope Olofintuyi
                Aug 27, 2021 at 7:42
The NoneType is the type of the value None.   In this case, the variable lifetime has a  value of None.
A common way to have this happen is to call a function missing a return.
There are an infinite number of other ways to set a variable to None, however.
                I don't think lifetime had a value of None (pre-edit).  He was trying to access the lifetime attribute of something else that was None.
– g.d.d.c
                Nov 14, 2014 at 3:09
                else: pass is completely useless; if you don't have anything to put in else:, simply omit it.
– tripleee
                Nov 6, 2022 at 8:49
It means the object you are trying to access None. None is a Null variable in python.
This type of error is occure de to your code is something like this.
x1 = None
print(x1.something)
x1 = None
x1.someother = "Hellow world"
x1 = None
x1.some_func()
# you can avoid some of these error by adding this kind of check
if(x1 is not None):
    ... Do something here
else:
    print("X1 variable is Null or None")
When building a estimator (sklearn), if you forget to return self in the fit function, you get the same error.
class ImputeLags(BaseEstimator, TransformerMixin):
    def __init__(self, columns):
        self.columns = columns
    def fit(self, x, y=None):
        """ do something """
    def transfrom(self, x):
        return x
  
AttributeError: 'NoneType' object has no attribute 'transform'?
Adding return self to the fit function fixes the error.
                Perhaps it's worth pointing out that functions which do not explicitly return anything will implicitly return None. This is also the case if your function is basically if something: return value which will then  end up in the implicit return None limbo when something is not truthy. (The answer by PHINCY L PIOUS elaborates on this particular case.)
– tripleee
                Apr 7, 2022 at 4:52
                It is true that forgetting to return something in every scenario is a common bug for recursive functions in particular; but the exposition is this answer does not seem detailed enough to be actually useful. See the common FAQ stackoverflow.com/questions/17778372/…
– tripleee
                May 6 at 10:02
You can get this error with you have commented out HTML in a Flask application. Here the value for qual.date_expiry is None:
   <!-- <td>{{ qual.date_expiry.date() }}</td> -->
Delete the line or fix it up:
<td>{% if qual.date_attained != None %} {{ qual.date_attained.date() }} {% endif %} </td>
None of the other answers here gave me the correct solution. I had this scenario:
def my_method():
   if condition == 'whatever':
      return 'something'
   else:
      return None
answer = my_method()
if answer == None:
   print('Empty')
else:
   print('Not empty')
Which errored with:
File "/usr/local/lib/python3.9/site-packages/gitlab/base.py", line 105, in __eq__
if self.get_id() and other.get_id():
AttributeError: 'NoneType' object has no attribute 'get_id'
In this case you can't test equality to None with ==. To fix it I changed it to use is instead:
if answer is None:
   print('Empty')
else:
   print('Not empty')
                One of the lessons is to think hard about when return None creates more problems than it solves. In some cases, raising an exception might make more sense.
– tripleee
                Nov 6, 2022 at 8:49