[Python] How do I convert a Windows UNC path to a mapped drive letter path with Python?

I've seen the reverse of this question asked a lot but can't find info on this one.

A set of subprocesses I'm running in a script want Windows drive-letter paths (M:\Some\Path\file.txt instead of \\my.subnet\someplace\Some\Path\file.txt), but the UNC path is presented as an earlier input (which I don't have control over).

I am familiar with the pathlib.Path.drive function, which gives me \\my.subnet\subnet, but how would I get from that to the drive letter?

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