Custom formatters not working with modifiers (Undocumented breaking change in 0.24)

[ManuelHu]

Combining a custom format registered with @pint.register_unit_format and a modifier does not work on 0.24 any more. Apparently the formatter is silently not even called.

import pint

ureg = pint.get_application_registry().get()

@pint.register_unit_format("test")
def _test_format(unit, registry, **options):
    print("format called")
    proc = {u.replace("µ", "u"): e for u, e in unit.items()}
    fmt = pint.formatting if hasattr(pint, "formatting") else pint
    return fmt.formatter(
        proc.items(),
        as_ratio=True,
        single_denominator=False,
        product_fmt="*",
        division_fmt="/",
        power_fmt="{}{}",
        parentheses_fmt="({})",
        **options,
    )

base_unit = ureg.microsecond
print(f"with modifier - {base_unit:~test}")
print(f"without modifier - {base_unit:test}")

Output on pint 0.23

format called
with modifier - us
format called
without modifier - microsecond

Output on pint 0.24

with modifier - µs
format called
without modifier - microsecond

---

unfortunately we currently have to still support python 3.9, so only supporting pint 0.24+ is not an option for us, our code has to work on both versions... :-(

[hgrecco]

I think this is the same problem that is fixed in #2011

[ManuelHu]

I tried to apply that patch locally, and it does not work.

For more debuggin I added a print statement like this https://github.com/hgrecco/pint/pull/2011/files#diff-78134f4ee1d9944843acb020969e96a7d9541da73502c992a4fa1a1567251154L105:

     def get_formatter(self, spec: str):
         if spec == "":
             return self._formatters["D"]
         for k, v in self._formatters.items():
             if k in spec:
                 return v
+        print(spec)
         try:
             orphan_fmt = REGISTERED_FORMATTERS[spec]
         except KeyError:
             return self._formatters["D"]

which gives a spec of ~test in my testcase above. And that format spec is certainly not defined, as it still contains the ~ modifier - so the default Dformat spec is used.

[hgrecco]

The problem is that is returning an orphan formatter (i.e. one not attached to the registry)

Try replacing:

        try:
            orphan_fmt = REGISTERED_FORMATTERS[spec]
        except KeyError:
            return self._formatters["D"]

by

        for k, v in REGISTERED_FORMATTERS.items():
            if k in spec:
                orphan_fmt = REGISTERED_FORMATTERS[spec]
                break
        else:
            return self._formatters["D"]

Please notice that the check is: if k in spec:. That means that if k == test and spec == ~test this should return the right formatter.

If it works, please submit a PR linking to @2011 ping: @andrewgsavage

[andrewgsavage]

should be working now