Unreachable ‘except’ block¶
ID: py/unreachable-except Kind: problem Severity: error Precision: very-high Tags: - reliability - maintainability - external/cwe/cwe-561 Query suites: - python-security-and-quality.qls
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When handling an exception, Python searches the except blocks in source code order until it finds a matching
except block for the exception. An except block,
except E:, specifies a class
E and will match any exception that is an instance of
If a more general except block precedes a more specific except block, then the more general block is always executed and the more specific block is never executed. An except block,
except A:, is more general than another except block,
except B:, if
A is a super class of
except Exception: is more general than
except Error: as
Exception is a super class of
except blocks so that the more specific
except is defined first. Alternatively, if the more specific
except block is no longer required then it should be deleted.
In this example the
except Exception: will handle
AttributeError preventing the subsequent handler from ever executing.
def incorrect_except_order(val): try: val.attr except Exception: print ("Exception") except AttributeError: print ("AttributeError")
Python Language Reference: The try statement, Exceptions.
Common Weakness Enumeration: CWE-561.