[issue42646] Add function that supports "applying" methods

[Josh Rosenberg]

Josh Rosenberg  added the comment:

If you're annoyed by having to use two lines, one to copy, one to call the 
mutating method, you can use the walrus operator:

(y := x.copy()).some_method()

or:

(y := deepcopy(x)).some_method()

Does that cover your use case?

For the list case, you'd normally just do:

arr = lis[::-1]

but:

(arr = lis.copy()).reverse()

also works.

Granted, not super pretty. But I'm not seeing enough cases where this ugliness 
is truly unavoidable (the two lines don't bother me that much, and for 
built-ins, there is usually a one-liner that works fine, e.g. the reversing 
slice as shown, sorted over list.sort, etc.).

I'll note: Unconditionally calling copy.copy is fine; it knows to try the 
__copy__ method of the things it is called on (and most things that offer copy 
alias it to __copy__ or are special-cased in copy.copy as well; if they don't, 
they should), so you're unlikely to need to perform the "try method, fall back 
to copy.copy" yourself.

--
nosy: +josh.r

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[issue42646] Add function that supports "applying" methods

[Eric V. Smith]

Eric V. Smith  added the comment:

This seems way too special case for the stdlib, and especially not as a 
builtin. I've never seen this pattern before. Why is copy so special?

I suggest raising this on the python-ideas mailing list if you'd like to get 
some traction for it.

--
nosy: +eric.smith
type:  -> enhancement

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[issue42646] Add function that supports "applying" methods

[wyz23x2]

wyz23x2  added the comment:

Edit: applied should be the better name because of reversed(), sorted() etc. 
and doesn't conflict with Py 2.

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[issue42646] Add function that supports "applying" methods

[wyz23x2]

New submission from wyz23x2 :

Doing this is generally very annoying:
y = x.copy()
y.some_method()
Sometimes x doesn't have copy(), so:
from copy import deepcopy
y = deepcopy(x)
y.some_method()

So maybe a function could be added to help.
For example:

def apply(obj, function, /, args=(), kwargs={}):
try:
new = obj.copy()
except AttributeError:
from copy import copy
new = copy(obj)
function(new, *args, **kwargs)
return new
# implement reversed() for list
lis = [1, 2, 3, 4, 5]
arr = apply(lis, list.reverse)
print(arr)  # [5, 4, 3, 2, 1]

apply() maybe isn't the best name because of the builtin apply() in Python 2, 
but that's EOL. It could be added in the standard library.

--
components: Library (Lib)
messages: 383050
nosy: wyz23x2
priority: normal
severity: normal
status: open
title: Add function that supports "applying" methods
versions: Python 3.10

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