Why does PyVerilator explicitly check for .v extension on files

[Duality4Y]

Why does PyVerilator explicitly check for the .v extension on files?
Is there a good reason for this?

here is the line:
https://github.com/csail-csg/pyverilator/blob/master/pyverilator/pyverilator.py#L409

what if you call your source files .sv for system verilog ? or .txt?
It shouldn't matter right?