units.quantity_input with annotated Quantity type hint in a Union causes error #17017
Description
Description
Hi!
I'm not sure if this is a bug report or feature request for unsupported use case.
I have a case where an argument could be either a Quantity or a string that will later be converted to quantity. I tried type hinting with Union[Quantity["angle"], str], but this causes the error shown below when using a string as the argument. See the minimal example below for the error when using the units.quantity_input decorator.
My understanding of the issue is it comes from the QuantityInput decorator: non-quantity parts of the Union are set to False and then dropped from valid_targets before the decorator performs a check on the quantity. Then if the argument is not a quantity the check will fail because the string has no units.
Thank you!
Expected behavior
The behavior I would have expected is that non-quantity types are considered as part of the Union when validating the input. I could see two ways to fix/support this:
- Recognize other types parts of
Unionand check if the argumentisinstanceof one of them when it's not aQuantity - When the type is a union, just drop validation, as would be the case with a non-annotated quantity. I think this is less desirable as it could let pass wrong units unexpectedly for users.
I could try implementing one of these if you think it is a good way forward.
How to Reproduce
- Install latest main branch from github
- Run the snippet below
- Get the error below the snippet
The code:
from typing import Union
import astropy.units as u
from astropy.units import Quantity
@u.quantity_input
def afun(length_or_str: Union[Quantity["length"], str]):
print(f"Worked with {length_or_str}")
afun(1 * u.m) # Works
afun("1m") # FailsThe error:
Worked with 1.0 m
Traceback (most recent call last):
File "/home/vandal/repos/astro/astropy/astropy/units/decorators.py", line 69, in _validate_arg_value
if arg.unit.is_equivalent(allowed_unit, equivalencies=equivalencies):
^^^^^^^^
AttributeError: 'str' object has no attribute 'unit'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/vandal/repos/astro/astropy/quantity_input_minimal.py", line 12, in <module>
afun("1m") # Fails
^^^^^^^^^^
File "/home/vandal/repos/astro/astropy/astropy/units/decorators.py", line 298, in wrapper
_validate_arg_value(
File "/home/vandal/repos/astro/astropy/astropy/units/decorators.py", line 78, in _validate_arg_value
raise TypeError(
TypeError: Argument 'length_or_str' to function 'afun' has no 'unit' attribute. You should pass in an astropy Quantity instead.Versions
import astropy
try:
astropy.system_info()
except AttributeError:
import platform; print(platform.platform())
import sys; print("Python", sys.version)
import astropy; print("astropy", astropy.__version__)
import numpy; print("Numpy", numpy.__version__)
import erfa; print("pyerfa", erfa.__version__)
try:
import scipy
print("Scipy", scipy.__version__)
except ImportError:
print("Scipy not installed")
try:
import matplotlib
print("Matplotlib", matplotlib.__version__)
except ImportError:
print("Matplotlib not installed")# Paste the result here
platform
--------
platform.platform() = 'Linux-6.10.9-arch1-2-x86_64-with-glibc2.40'
platform.version() = '#1 SMP PREEMPT_DYNAMIC Tue, 10 Sep 2024 14:37:32 +0000'
platform.python_version() = '3.12.5'
packages
--------
astropy 7.0.0.dev436+g3b88b55dfc
numpy 2.0.0
scipy 1.14.0
matplotlib 3.9.1
pandas 2.2.2
pyerfa 2.0.1.4