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default-except-not-last (F707)

Added in v0.0.28 · Related issues · View source

Derived from the Pyflakes linter.

What it does

Checks for except blocks that handle all exceptions, but are not the last except block in a try statement.

Why is this bad?

When an exception is raised within a try block, the except blocks are evaluated in order, and the first matching block is executed. If an except block handles all exceptions, but isn't the last block, Python will raise a SyntaxError, as the following blocks would never be executed.

Example

def reciprocal(n):
    try:
        reciprocal = 1 / n
    except:
        print("An exception occurred.")
    except ZeroDivisionError:
        print("Cannot divide by zero.")
    else:
        return reciprocal

Use instead:

def reciprocal(n):
    try:
        reciprocal = 1 / n
    except ZeroDivisionError:
        print("Cannot divide by zero.")
    except:
        print("An exception occurred.")
    else:
        return reciprocal

References