The only two possible types for an except's expression are a class deriving from BaseException, or a tuple composed of such classes.

This rule raises an issue when the expression used in an except block is a boolean expression of exceptions. The result of such expression is a single exception class, which is valid but not what the developer intended.

Noncompliant Code Example

try:
    raise TypeError()
except ValueError or TypeError:  # Noncompliant
    print("Catching only ValueError")
except ValueError and TypeError:  # Noncompliant
    print("catching only TypeError")
except (ValueError or TypeError) as exception:  # Noncompliant
    print("Catching only ValueError")

foo = ValueError or TypeError  # foo == ValueError
foo = ValueError and TypeError  # foo == TypeError

Compliant Solution

try:
    raise TypeError()
except (ValueError, TypeError) as exception:
    print("Catching all exceptions")

See

• Python documentation - the try statement