Attempting to raise an object which does not derive from BaseException will raise a TypeError.
If you are about to create a custom exception class, note that custom exceptions should inherit from Exception, rather than
BaseException.
BaseException is the base class for all built-in exceptions in Python, including system-exiting exceptions like
SystemExit or KeyboardInterrupt, which are typically not meant to be caught. On the other hand, Exception is
intended for exceptions that are expected to be caught, which is generally the case for user-defined exceptions. See PEP 352 for more information.
To fix this issue, make sure that the object you’re attempting to raise inherits from BaseException.
Code examples
Noncompliant code example
raise "Something went wrong" # Noncompliant: a string is not a valid exception
class A:
pass
raise A # Noncompliant: A does not inherit from Exception
Compliant solution
class MyError(Exception):
pass
raise MyError("Something went wrong")
raise MyError
Note: In Python 2 it is possible to raise old-style classes but this shouldn’t be done in order to be compatible with Python
3.
