[issue36039] Replace append loops with list comprehensions

[Lukas Geiger]

Lukas Geiger  added the comment:

Thank you very much for your thorough explanation, totally makes sense.

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[issue36039] Replace append loops with list comprehensions

[Raymond Hettinger]

Raymond Hettinger  added the comment:

I concur with all the other -1 comments and will mark this a closed.

FWIW, we generally discourage sweeping across the library with minor rewrites.  
Guido articulated a principle of "holistic refactoring" where we make code 
improvements while working on the module as a whole.  This helps makes sure 
that code changes are made in the context of a thorough understanding of what 
the module is trying to do.  This also helps us reduce maintenance-induced-bugs 
where minor code adjustments create new bugs that weren't there before.

Thank you for taking a look at the source and please continue to do so. If you 
find a specific case that is problematic, feel free to post that one particular 
case.  That said, a better use of time is to take one of the many open tracker 
issues, research it, and propose a fix.

--
nosy: +rhettinger
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue36039] Replace append loops with list comprehensions

[Rémi Lapeyre]

Rémi Lapeyre  added the comment:

In some places, using a lot is also a deliberate choice to improve readability.

I think the boy scout rule is more appropriate for such changes.

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nosy: +remi.lapeyre

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[issue36039] Replace append loops with list comprehensions

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

Agreed with @p-ganssle . Similar issue33152 in the past for the refactoring in 
timeit module to use list comprehension. Large refactorings like this could 
also make git blame little more difficult in places where this has less benefit 
like smaller lists for common cases. I think it's much better to identify hot 
code paths with potentially large lists that could benefit from this along with 
a benchmark that could be accepted by the core dev/maintainer of the module.

--
nosy: +xtreak

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[issue36039] Replace append loops with list comprehensions

[Paul Ganssle]

Paul Ganssle  added the comment:

I think I'm -1 on a general project or policy to replace all for-append loops 
with list comprehensions, but I'm generally positive about individual 
improvements to the code base, on a case-by-case basis.

I can't speak for anyone but myself, but I imagine that if you can identify a 
few places where this sort of change would make a significant performance 
improvement, it would be well-received.

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nosy: +p-ganssle

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[issue36039] Replace append loops with list comprehensions

[Lukas Geiger]

New submission from Lukas Geiger :

Lib uses loops to append to a new list in quite a few places. I think it would 
be better to replace those with list comprehensions.

Benefits of this change:
  - List comprehensions are generally more readable than appending to a newly 
created list
  - List comprehensions are also a lot faster.
Toy example:
In [1]: %%timeit
   ...: l = []
   ...: for i in range(5000):
   ...: l.append(i)
375 µs ± 1.73 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

In [2]: %%timeit
   ...: l = [i for i in range(5000)]
168 µs ± 1.08 µs per loop (mean ± std. dev. of 7 runs, 1 loops each)

Possible drawbacks:
  - Refactoring can always introduce bugs and makes it harder to get meaningful 
output from git blame. In this case I think the diff is very manageable, making 
the changes easy to review.

Personally, I think the codebase would benefit from this change both in terms 
of some small performance gains and maintainability. I'd be happy to make a PR 
to fix this.

--
components: Library (Lib)
messages: 335961
nosy: lgeiger
priority: normal
severity: normal
status: open
title: Replace append loops with list comprehensions
type: performance
versions: Python 3.8

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