List Comprehension as Compulsory Functional Style

[vbrozik (Václav Brožík)]

I will try to not make my reply too long.

I have to admit that my reaction which started this, was probably too strict:

Removing sublist if matching a criteria

Please, nooo This is against important good manners in programming style, a way how to create obscure code. The comprehensions / generator expressions are functional style. You are supposed to read data, and make new data from them. Here you are modifying the original data using the methods list.pop() and list.remove(). Please do not misuse comprehensions as another way to write a for loop. If you want to perform side-effects, use a for loop. No, this code checks that a strin…

It is my point of view how readable code should look like. I still strongly stand by this statement: Please do not misuse comprehensions as another way to write a for loop.

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@mlgtechuser

I’ve not seen anything about minimizing ways to accomplish something, but rather there seems to be a bounty of different ways, with the goal of doing it the “most Pythonic” way.

The principles of readability and intended use I see as the “Pythonic” way. I do not think that the intended use should be followed always but I think in both the examples there should not be modification of the input data inside the comprehension.

@mlgtechuser

A given context has many facets (speed, resource usage, size of the code file, etc.).

Yes, but when you start with these facets too early, it is called premature optimization. In Python I prefer readability. It is important especially in cases when the code should be well understood by someone else. (It is certainly the case of code in this forum.)

When the optimization causes the code to be less readable, it should be well explained in comments.

@mlgtechuser

List comprehensions provide a concise way to create lists. Common applications are to make new lists

True, but it doesn’t say that they “aren’t a concise way to iterate over a list and shouldn’t be used for this purpose”.

…as above, doesn’t prohibit list comprehension from being used as a concise for: loop.

I still think the readability will suffer if you go away from the original intention how to use comprehensions. You do not need to be prohibited from doing something to feel that it is not a good way.

@mlgtechuser

comprehensions can provide a more syntactically succinct idiom than the traditional for loop.
[sic: original says “idiom that the”]

This reference explicitly endorses use of list comprehension for conciseness.

Yes, but I certainly understand the statement in the context that it is for the cases when the shorter code improves readability. I am convinced that this only happens when the comprehensions are not too complex.

In general I think that the urge to squeeze a lot of code to small number of lines is a very bad practice. It is good for puzzles like code-golfing though. How much time do you need to analyze the following code?

from functools import reduce
print(*filter(None,map(lambda y:y*reduce(lambda x,y:x*y!=0,
map(lambda x,y=y:y%x,range(2,int(pow(y,.5)+1))),1),range(2,1000))))

Solution and source: Programming FAQ — Python 3.12.1 documentation

As they said:

Don’t try this at home, kids!

My conclusion: In Python readability first