provide .copy() method for both SourmashSignature() and MinHash

[ctb]

I'm getting tired of using copy.copy(...) 😆

The idea here is to:

• provide copy methods on both the SourmashSignature and MinHash classes. Naively, copy.copy(self) should work?
• replace the calls to copy.copy(...) in the current sourmash code with the new method.

[ctb]

note that MinHash in src/sourmash/minhash.py already contains a __copy__(self) method, could just add a copy = __copy__ below that. (And write some tests.)

[ctb]

actually, if we go with #1508, then we won't need .copy() for MinHash objects because you will instead just call mutable() or frozen() to get a copy for your desired purpose. Maybe we want to take a similar approach with SourmashSignature in the future?

[keyabarve]

I would like to work on this. @ctb

[keyabarve]

Could you provide a little clarification on what needs to be done here? Which files/functions need to be changed, etc.

[ctb]

Here's some reading, too - https://docs.python.org/3/library/copy.html,

In order for a class to define its own copy implementation, it can define special methods __copy__() and __deepcopy__(). The former is called to implement the shallow copy operation; no additional arguments are passed.

So:

1. define __copy__(...) and copy(...) methods on MinHash subclasses in src/sourmash/minhash.py
2. define __copy__(...) and copy(...) methods on SourmashSignature in src/sourmash/signature.py
3. write tests to make sure they work properly, in tests/test_minhash.py and tests/test_signature.py respectively.

[keyabarve]

Thanks, I will check it out!