74 lines
2.4 KiB
Plaintext
74 lines
2.4 KiB
Plaintext
Exceptions handlers (``++except:++``) are evaluated in the order they are written. Once a match is found, the evaluation stops.
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In some contexts an except block is dead code as it will never catch any exception:
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* If there is a handler for a base class followed by a handler for class derived from that base class, the second handler will never trigger: The handler for the base class will match the derived class, and will be the only executed handler.
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* When multiple ``++except++`` statements try to catch the same exception class, only the first one will be executed.
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* In python 3, ``++BaseException++`` is the parent of every exception class. When ``++BaseException++`` is caught and the same try-except block has a bare ``++except:++`` statement, i.e. an ``++except++`` with no expression, the bare except will never catch anything.
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This rule raises an issue when an ``++except++`` block catches every exception before a later ``++except++`` block could catch it.
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== Noncompliant Code Example
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----
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def foo():
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try:
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raise FloatingPointError()
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except (ArithmeticError, RuntimeError) as e:
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print(e)
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except FloatingPointError as e: # Noncompliant. FloatingPointError is a subclass of ArithmeticError
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print("Never executed")
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except OverflowError as e: # Noncompliant. OverflowError is a subclass of ArithmeticError
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print("Never executed")
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try:
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raise TypeError()
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except TypeError as e:
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print(e)
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except TypeError as e: # Noncompliant. Duplicate Except.
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print("Never executed")
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try:
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raise ValueError()
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except BaseException as e:
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print(e)
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except: # Noncompliant. This is equivalent to "except BaseException" block
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print("Never executed")
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----
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== Compliant Solution
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----
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def foo():
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try:
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raise FloatingPointError()
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except FloatingPointError as e:
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print("Executed")
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except OverflowError as e:
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print("Executed")
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except (ArithmeticError, RuntimeError) as e:
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print(e)
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try:
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raise TypeError()
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except TypeError as e:
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print(e)
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try:
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raise ValueError()
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except BaseException as e:
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print(e)
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----
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== See
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* Python Documentation - https://docs.python.org/3/reference/compound_stmts.html#the-try-statement[The ``++try++`` statement]
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ifdef::rspecator-view[]
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== Comments And Links
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(visible only on this page)
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include::../comments-and-links.adoc[]
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endif::rspecator-view[]
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