Python 3 exception deletes variable in enclosing scope for unknown reason [duplicate]
Quoting the documentation of try,
When an exception has been assigned using
as target, it is cleared at the end of the except clause. This is as ifexcept E as N: foowas translated to
except E as N: try: foo finally: del NThis means the exception must be assigned to a different name to be able to refer to it after the except clause. Exceptions are cleared because with the traceback attached to them, they form a reference cycle with the stack frame, keeping all locals in that frame alive until the next garbage collection occurs.
This is covered in these two PEPs.