Pint should validate aliases

[dalito]

Currently it is possible to define invalid and unusable aliases. In contrast to unit names, alias names are obviously not sufficiently validated.

Python 3.11.7 (tags/v3.11.7:fa7a6f2, Dec  4 2023, 19:24:49) [MSC v.1937 64 bit (AMD64)] on win32
>>> import pint
>>> pint.__version__
'0.23'
>>> ureg = pint.UnitRegistry()
>>> ureg.define("@alias meter = my'dog")
>>> ureg("m").to("my'dog")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\dlinke\MyProg_local\gh-dalito\ucumvert\.venv\Lib\site-packages\pint\facets\plain\quantity.py", line 526, in to
    other = to_units_container(other, self._REGISTRY)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\dlinke\MyProg_local\gh-dalito\ucumvert\.venv\Lib\site-packages\pint\util.py", line 1046, in to_units_container
    return registry.parse_units_as_container(unit_like)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\dlinke\MyProg_local\gh-dalito\ucumvert\.venv\Lib\site-packages\pint\facets\nonmultiplicative\registry.py", line 70, in parse_units_as_container
    return super().parse_units_as_container(input_string, as_delta, case_sensitive)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\dlinke\MyProg_local\gh-dalito\ucumvert\.venv\Lib\site-packages\pint\facets\plain\registry.py", line 1204, in parse_units_as_container
    return self._parse_units_as_container(input_string, as_delta, case_sensitive)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\dlinke\MyProg_local\gh-dalito\ucumvert\.venv\Lib\site-packages\pint\facets\plain\registry.py", line 1239, in _parse_units_as_container
    cname = self.get_name(name, case_sensitive=case_sensitive)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\dlinke\MyProg_local\gh-dalito\ucumvert\.venv\Lib\site-packages\pint\facets\plain\registry.py", line 647, in get_name
    raise UndefinedUnitError(name_or_alias)
pint.errors.UndefinedUnitError: 'my' is not defined in the unit registry
>>>ureg("m").to("my")  # So is maybe "my" defined by wrong parsing?
(...)
pint.errors.UndefinedUnitError: 'my' is not defined in the unit registry

[hgrecco]

I agree. Alias and unit names must be validated. I think they must follow the same rules as python identifiers.

[dalito]

The unit names are already properly validated. So validation code is already written just not applied to aliases.

[hgrecco]

indeed! Will fix it!

[hgrecco]

The code is there already Just need to swap the function for is_valid_unit_alias. Not sure why it is _no_space instead of str.isidentifier. I will try to look at the history to see if there was any reason that I should tackle before.

But I agree with you, an alias should follow the same rule as a unit name.

[hgrecco]

It turns out it is not so easy. Some alias that we want to have like °C are not valid identifiers. We will need to improve the function currently named _no_space. What else we need to check in addition that there are no spaces?

>>> str.isidentifier("°C")
False