Problem with Setuptools

[metroid120]

Hello guys, I have found a problem with setuptools.

In File quantity.py I needed to replace:
from pkg_resources.extern.packaging import version

with
# from packaging import version

I think pkg_resources.extern is no longer provided by setuptools.
This is the first time I am writing something on Github, maybe you can point me to
a resource or tell me what to do in case I find such bugs in open sources projects.

[hgrecco]

Cannot reproduce. Please provide the versions of the different packages you are using.

[metroid120]

I am using:
-setuptools 44.0.0
-pint 0.10.2dev branch
-python 3.8.1

[hgrecco]

I think your installation of setuptools is incomplete as packaging is included within the extern part of setuptools. Are you running this on linux, by chance?

[metroid120]

Yes I am using linux (arch).

[hgrecco]

I am pretty sure that you setuptools instalation is broken. packaging is an extern part of setuptools. Maybe this happened or similar. I would suggest you do a clean install. I am closing now, feel free to reopen if needed.

[dev-zero]

Since I hit the very same issue after doing a pip install --user myproject which depends on pint I followed the leads a bit. The cause is that some Linux distributions like Arch Linux have stopped including the vendored packaging package (which was part of setuptools):

• https://git.archlinux.org/svntogit/packages.git/tree/trunk/PKGBUILD?h=packages/python-setuptools
• vendoring logic subtly breaks later usage of unvendored system versions after importing pkg_resources.extern pypa/setuptools#1383

So yes, you should directly be using packaging rather than relying on setuptools' import of the packaging library to make it work in any case.

[keewis]

thanks for investigating. My reason for choosing to use pkg_resources.extern.packaging instead of directly using packaging was to avoid adding another (direct) dependency to pint. If that decision causes problems, I guess we should change that (unless there are any objections?).

Do you want to submit a PR?

[jules-ch]

Btw pkg_resources from setuptools can be replaced with standard library importlib.metadata & importlib.resources from Python 3.8 & Python 3.7 respectively.

There are backports for both.

[keewis]

thanks for the tip. Unless I'm missing something, neither of those libraries provide version comparison, though? (distutils does, but neither LooseVersion nor StrictVersion correctly compare the versions setuptools_scm creates)

[dev-zero]

and Duck typing wouldn't work?

    def __matmul__(self, other):
        try:
            # Use NumPy ufunc (existing since 1.16) for matrix multiplication
            return np.matmul(self, other)
        except AttributeError:
            return NotImplemented

[keewis]

numpy.matmul was introduced in 1.10, but it wasn't a ufunc until 1.16 (making it overridable using __array_ufunc__). Since the minimum numpy version pint supports is 1.14, I think we still need the version check (but I might be mistaken).

@jthielen, any thoughts on this?

[jthielen]

@keewis Indeed, np.matmul's behavior is only correct with Pint Quantities since version 1.16 when it became a ufunc, so checking for an AttributeError in Quantity's __matmul__ would be insufficient. To remove the version check (or to work with NumPy pre-1.16), there would need to be custom unit checking/handling code in __matmul__. When implementing __matmul__ here, I had assumed most people would be on recent NumPy versions, so that it wasn't worth the effort, and the version check was good enough.

However, if the version check needs to be removed, I'm sure a PR would be welcome to do so.

[keewis]

I think it should be enough to add the (currently indirect) dependency packaging as a direct dependency, change the import and remove the version check once we require numpy >= 1.16.

The numpy support for pint>=0.10 heavily depends on recent numpy features, so unless someone has to use matrix multiplication with numpy<0.16 (and maybe puts in a PR), I'd try to avoid increasing the code complexity.

With that said, @dev-zero: do you want to put in a PR? Otherwise I'd do it.