Python does not have explicit variable declarations. It is implicitly created by the assignment. That means to understand a piece of code, specificly, to understand a life time of a variable, one has to hunt down the first occurence of assignment.
In Perl, with use strict, which should be on always, it is a simple matter of searching for keyword my or our. The life time of a local variable starts at the my $var to the end of the scope, period.