Update copy.py

[rajucomp]

I think that some code was being repeated because of an if else condition. I tried to combine them into one. Would loved to know the thoughts of the community.

[bedevere-bot]

Most changes to Python require a NEWS entry.

Please add it using the blurb_it web app or the blurb command-line tool.

[ghost]

All commit authors signed the Contributor License Agreement.

[sunmy2019]

What we have done here is called https://en.wikipedia.org/wiki/Loop_unswitching

It may cause a performance penalty. Have you done benchmarks?

[Abbasi393]

LGTM

[Eclips4]

Hello!
Please, provide an results of benchmarks after(and before) this change.
If performance difference is not significantly, core developers doesn't merge this PR.
CPython core developers as a rule, doesn't merge cosmetic changes.

[AlexWaygood]

@arhadthedev, please don't add "skip issue" and "skip news" to PRs like this:

• Requiring an issue means that contributors need to state a clear rationale for their change, in words. Reviewing PRs is much easier if a contributor has clearly explained, in words, why the change is desirable.
• Requiring a NEWS entry means that contributors need to explain the impact that their change has on users of the API that they're changing:
  • If there's no impact to users, then the change probably doesn't need to be made at all, and the PR should be closed.
  • If there is an impact to users, then the users deserve to know about it, so there should be a NEWS entry.

[bedevere-bot]

Most changes to Python require a NEWS entry.

Please add it using the blurb_it web app or the blurb command-line tool.

[AlexWaygood]

@rajucomp, thank you for the PR! I agree that the code looks slightly simpler and less repetitive this way. However, I'm going to reject this PR, for three reasons:

1. I can't find any performance difference from this PR. I've tried the pyperformance deepcopy benchmark, and a number of microbenchmarks, locally, and this PR doesn't seem to impact the execution time of any of them, unfortunately. If you're able to construct a benchmark that this PR improves, please post it here, and I'll be happy to reconsider :)

2. CPython generally does not accept PRs that only make "cosmetic" changes to code. This is because any change, no matter how small, carries with it a certain risk of causing breakage -- and breakages in the standard library have a very high impact on users of Python. It's also to avoid unnecessary code churn and make git blame easy to read.

3. Although there doesn't seem to be a real performance difference either way, it is more obvious from reading the existing (more verbose) code that it will have optimal performance. With your patch, you would do this, which would involve doing the if deep: check with every iteration of the for item in listiter loop:

   for item in listiter:
       if deep:
           item = deepcopy(item, memo)
       y.append(item)

   Whereas with the existing (more verbose code), we only have to do the if deep: check once. In practical terms, as I say, it doesn't seem to make a performance difference -- but it is "more obviously correct" for human readers of the code, even though it is more verbose and might seem more repetitive:

   if deep:
       for item in listiter:
           item = deepcopy(item, memo)
           y.append(item)
   else:
       for item in listiter:
           y.append(item)

Thanks again for the PR, though, and for your interest in improving CPython!