Issue using currency symbols ($, €)

[simaosr]

Hello,

I'm trying to use Pint 0.23 to handle currency conversion. I'm creating my currency units with

# Create UnitRegistry
ureg = UnitRegistry()

# Create currency dimension
ureg.define("USD = [currency]")
ureg.define("EUR = 1.14 USD = €")
ureg.define("GBP = 1.17 USD = £")

However, whenever I try to handle any unit defined using the symbol (alone), I get the following error:

Traceback (most recent call last):
File ", line 19, in
a = ureg("$")
File "venv\lib\site-packages\pint\facets\plain\registry.py", line 1388, in parse_expression
return build_eval_tree(gen).evaluate(_define_op)
File "venv\lib\site-packages\pint\pint_eval.py", line 566, in build_eval_tree
result, _ = _build_eval_tree(tokens, op_priority, 0, 0)
File "venv\lib\site-packages\pint\pint_eval.py", line 515, in _build_eval_tree
assert result is not None
AssertionError

If I try to use the symbol with another unit ("$/Mt" for example) I get the following error:

File "venv\lib\site-packages\pint\util.py", line 767, in from_string
ret = build_eval_tree(gen).evaluate(
File "venv\lib\site-packages\pint\pint_eval.py", line 392, in evaluate
raise DefinitionSyntaxError(f"missing unary operator '{op_text}'")
pint.errors.DefinitionSyntaxError: missing unary operator '/'

Has anyone faced this issue, or know how to handle this properly?

Thank you in advance.

[OJFord]

@simaosr How did you resolve it?

I have the same (latter) issue in python 3.11 with code working fine in 3.12.

[simaosr]

Hi @OJFord

I solved it using the solution given in the comments of #1814

import pint
ureg = pint.UnitRegistry(preprocessors = [lambda s: s.replace("€", "EUR")])
ureg.define("euro = [currency] = € = EUR")

print(ureg.Quantity("1 €"))
# I get "1 euro", it works!

[OJFord]

Ah, thanks! I eventually figured out the replacement, but I didn't know about preprocessors - that's tidier.

[andrewgsavage]

We should add a page to the docs for this - I'll leave this issue open until there's one