CodeQL documentation

Non-callable called

ID: py/call-to-non-callable
Kind: problem
Severity: error
Precision: high
Tags:
   - reliability
   - correctness
   - types
Query suites:
   - python-security-and-quality.qls

Click to see the query in the CodeQL repository

If an object is called, obj(), then that object must be a callable or a TypeError will be raised. A callable object is any object whose class defines the __call__ special method. Callable objects include functions, methods, classes.

The callable(object) builtin function determines if an object is callable or not.

When the Python interpreter attempts to evaluate a call such as func(arg) it will invoke the __call__ special method on func. Thus, func(arg) is roughly equivalent to type(func).__call__(func, arg) which means that the class must define the attribute __call__, merely adding it to the instance is not sufficient.

Recommendation

Since this problem usually indicates a logical error, it is not possible to give a general recipe for fixing it.

Example

lists are not callable. In this example, an attempt is made to call a list which will fail with a TypeError.

a_list = []
a_list()

References