element.py: fix unbounded variable in nested python exception

Description

As per https://docs.python.org/3.7/reference/compound_stmts.html#except
variables used in the "except" clause are erased at the end of the
block.

We had a conflict with a nested exception using the same variable as
before.

This renames the nested variable to avoid the clash

Changes proposed in this merge request:

• rename internal variable to avoid clash

This merge request, when approved, will close:

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