What does "TypeError 'xxx' object is not callable" means?

The exception is raised when you try to call not callable object. Callable objects are (functions, methods, objects with __call__)

>>> f = 1
>>> callable(f)
False
>>> f()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable

The other answers detail the reason for the error. A possible cause (to check) may be your class has a variable and method with the same name, which you then call. Python accesses the variable as a callable - with ().

e.g. Class A defines self.a and self.a():

>>> class A:
...     def __init__(self, val):
...         self.a = val
...     def a(self):
...         return self.a
...
>>> my_a = A(12)
>>> val = my_a.a()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable
>>>

That error occurs when you try to call, with (), an object that is not callable.

A callable object can be a function or a class (that implements __call__ method). According to Python Docs:

object.__call__(self[, args...]): Called when the instance is “called” as a function

For example:

x = 1
print x()

x is not a callable object, but you are trying to call it as if it were it. This example produces the error:

TypeError: 'int' object is not callable

---

For better understaing of what is a callable object read this answer in another SO post.

The action occurs when you attempt to call an object which is not a function, as with (). For instance, this will produce the error:

>>> a = 5
>>> a()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable

Class instances can also be called if they define a method __call__

One common mistake that causes this error is trying to look up a list or dictionary element, but using parentheses instead of square brackets, i.e. (0) instead of [0]