Why do I get AttributeError: 'NoneType' object has no attribute 'something'?

问题

I keep getting an error that says

AttributeError: \'NoneType\' object has no attribute \'something\'

The code I have is too long to post here. What general scenarios would cause this AttributeError, what is NoneType supposed to mean and how can I narrow down what\'s going on?

回答1:

NoneType means that instead of an instance of whatever Class or Object you think you're working with, you've actually got None. That usually means that an assignment or function call up above failed or returned an unexpected result.

回答2:

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

or

foo = None
print foo.something

Both will yield an AttributeError: 'NoneType'

回答3:

Others have explained what NoneType is and a common way of ending up with it (i.e., failure to return a value from a function).

Another common reason you have None where you don't expect it is assignment of an in-place operation on a mutable object. For example:

mylist = mylist.sort()

The sort() method of a list sorts the list in-place, that is, mylist is modified. But the actual return value of the method is None and not the list sorted. So you've just assigned None to mylist. If you next try to do, say, mylist.append(1) Python will give you this error.

回答4:

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.

回答5:

Consider the code below.

def return_something(someint):
 if  someint > 5:
    return someint

y = return_something(2)
y.real()

This is going to give you the error

AttributeError: 'NoneType' object has no attribute 'real'

So points are as below.

1. In the code, a function or class method is not returning anything or returning the None
2. Then you try to access an attribute of that returned object(which is None), causing the error message.

回答6:

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)

#or

x1 = None
x1.someother = "Hellow world"

#or
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")

回答7:

g.d.d.c. is right, but adding a very frequent example:

You might call this function in a recursive form. In that case, you might end up at null pointer or NoneType. In that case, you can get this error. So before accessing an attribute of that parameter check if it's not NoneType.

回答8:

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>

来源：https://stackoverflow.com/questions/8949252/why-do-i-get-attributeerror-nonetype-object-has-no-attribute-something