Exception when creating copy of Option object with Constraint

[MePsyDuck]

Using:

• python 3.10
• click 8.1.7
• cloup 3.0.0

Bug description

Any class that extends cloup.constraints.Constraint cannot be copied via copy package or copy() method.

To Reproduce

Here's a minimal example to reproduce the issue

import copy
from cloup.constraints import Constraint

class MyConstraint(Constraint):
    def help(self, ctx):
        return 'help text'

    def check_values(self, params, ctx):
        pass

print(getattr(MyConstraint(), "__reduce_ex__", None)) # return non-None value
copy.copy(MyConstraint()) # produces error
MyConstraint().copy() # produces error

Output

Traceback (most recent call last):
  File ".../test.py", line 12, in test
    copy.copy(MyConstraint())
  File ".../python3.10/copy.py", line 92, in copy
    rv = reductor(4)
TypeError: 'NoneType' object is not callable

A library that I use (click-extra) uses deepmerge to build a parameter tree. When attempting to make a deepcopy of the Option object, a copy of the constraint is necessary, but instead it results in the exception mentioned above.

Since my understanding of Python is limited, I'm unable to debug the issue on my own. However, I have managed to narrow down the problem to this point. If there's a way I can assist in resolving this issue, please let me know.

[janluke]

Thanks for reporting. I'm quite busy these days but I'll see what I can do this week. Otherwise, @kdeldycke feel free to have a look at it :)

[janluke]

Fix released in v3.0.1.

[kdeldycke]

Oh thank both of you for this! Thank you @MePsyDuck for taking the time to dig in into Click Extra internals, and post an issue here, even if you don't know Python. 🤗

I was not aware of this issue and used deepmerge a little bit blindly, not knowing its detailed implementation. But now, in light of @janluke fix I get it.

Huge respect for you @janluke for looking into it and cutting a release while being busy. 💪 Also busy myself so I'll make the effort to release a new bug-fix version of Click Extra too. 😅

[MePsyDuck]

Great to see the issue resolved in version 3.0.1! Thanks, @janluke , for the quick fix despite your busy schedule.
Also, thank you, @kdeldycke , for your kind words! I'm glad I could contribute. Looking forward to continued improvements.

[janluke]

But now, in light of @janluke fix I get it.

I actually don't have a full understanding of it :D. I replicated the issue and read an error message that didn't make any sense:

I just thought it might be related to __getattr__ and noticed the mistake.