Signature mismatch in overriding method¶
ID: py/inheritance/signature-mismatch
Kind: problem
Security severity:
Severity: warning
Precision: very-high
Tags:
- quality
- reliability
- correctness
Query suites:
- python-security-and-quality.qls
Click to see the query in the CodeQL repository
There are one (or more) legal parameters for an overridden method that are not legal for an overriding method. This will cause an error when the overriding method is called with a number of parameters that is legal for the overridden method. This violates the Liskov substitution principle.
Recommendation¶
Ensure that the overriding method accepts all the parameters that are legal for overridden method.
Example¶
In this example there is a mismatch between the legal parameters for the base class method (self, source, filename, symbol) and the extension method (self, source). The extension method can be used to override the base method as long as values are not specified for the filename and symbol parameters. If the extension method was passed the additional parameters accepted by the base method then an error would occur.
# Base class method
def runsource(self, source, filename="<input>", symbol="single"):
... # Definition
# Extend base class method
def runsource(self, source):
... # Definition
The extension method should be updated to support the filename and symbol parameters supported by the overridden method.
References¶
Wikipedia: Liskov Substitution Principle, Method overriding.