[bad_user]

FP means referential transparency. For-comprehensions operate on iterators and iterators are not FP, being a very dirty and mutable protocol.

Do not confuse FP with declarative programming or with laziness. FP often implies declarative APIs and laziness but not vice-versa.

[duckerude]

Python's comprehensions were lifted from Haskell, and its map and filter functions also operate on iterables. They can't be purely functional because of the surrounding language, but they do follow a functional style.

(expr for item in iterable if cond) is more or less another way to spell map(lambda item: expr, filter(lambda item: cond, iterable)), except readable.

You could define "functional programming" to absolutely require referential transparency, but that's not what the rest of the thread is doing.

[kthielen]

I don't mean to be pedantic but IIRC Python's comprehensions actually came from the SETL language.

Obviously it's ultimately the same thing either way, but that's the lineage (SETL -> ABC -> Python).

https://en.wikipedia.org/wiki/SETL

[duckerude]

I didn't know about SETL, that's interesting.

https://docs.python.org/3/howto/functional.html#generator-ex... claims Python borrowed them from Haskell, but the ABC link seems more likely.

[zephyrfalcon]

ABC didn't have list comprehensions though, in spite of being influenced by SETL.

As I recall, Python did get them from Haskell, which in turn got them from Miranda, which got them from KRC. Before that it gets fuzzy, but it's likely that SETL was eventually at the root of it.