Support sq as a prefix representing ** 2

[rob-levy-minimum]

Pint ships with some "specialized" US area units like square_foot. When I discovered that there was an alias for this of sq_ft I thought that maybe sq might be a recognised prefix representing "square".

I was sad to find that sqm or sq_m doesn't exist. Given that sq_ft does exist in pint this seems like an anomaly.

We often use Pint to parse user-submitted data and our users think of "square metres" as "sqm".

Would it be possible for Pint to understand sqX to mean X ** 2? So, for example, sqcm or sq_cm would also be supported.

[andrewgsavage]

you can add sqm and others as definitions and aliases to default_en.txt. A PR adding these is welcomed.

I can see some difficulty in getting the parser to understand that the prefix changes the dimensionality (atm prefixes are only numerical multipliers), and with the formatting code. Therefore I don't think it's worth writing something to handle sq as an extra prefix

another option is to use a preprocessor to convert the string 'sq_cm' to 'cm ** 2' https://pint.readthedocs.io/en/stable/api/facets.html#pint.facets.plain.GenericPlainRegistry
This isn't documented yet - it would make a nice example.