Non-callable called¶
ID: py/call-to-non-callable
Kind: problem
Security severity:
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¶
Python Standard Library: callable.
Python Language Reference: object.call.