Kind of. Remember that a file can define more than one package, e.g. 
$ echo 'package A; package B; 1' > A.pm; perl -MA -le 'print for keys 
+%INC'
A.pm

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If you want to know if a package is defined, rather than whether a correspondingly-named file has been loaded, the OP's approach is correct.

In reply to Re^2: How to tell if a package is loaded by educated_foo
in thread How to tell if a package is loaded by mifflin

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