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Python	Analogue
functools.reduce	foldl
itertools.product
Indexing	fst and snd
functool.partial	Partial function application
itertools.accumulate	scanl
filter / itertools.compress	filter

General

• itertools.compress(l): make an iterator from a list ??
• itertools.cycle: Make infinite lists
• itertools.tee(it, n): Duplicate an iterator n times
• functools.lru_cache: memoize a function
  • The argument function better be pure

See:

• https://martinheinz.dev/blog/52

functools.reduce

• Kind of like foldl where first element is taken as accumulator.
• Error if iterable is empty.

Using example from docs:

>>> import functools as f
>>> f.reduce(lambda x, y: x+y, [1, 2, 3, 4, 5])
15
# ((((1+2)+3)+4)+5)

>>> f.reduce(lambda x, y: x+y, [4, 5])
9

>>> f.reduce(lambda x, y: x+y, [4])
4

>>> f.reduce(lambda x, y: x+y, [])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: reduce() of empty sequence with no initial value

itertools.product

>>> import itertools
>>> a=[1, 2, 3]
>>> b=[2, 3]
>>> [(i,j) for (i,j) in itertools.product(a,b)]

[(1, 2), (1, 3), (2, 2), (2, 3), (3, 2), (3, 3)]

Tuples: fst and snd

>>> a=(3,2)
>>> a[0]
3

>>> a[1]
2

>>> a[1:]
(2,)

Misc

• coconut: A Python-like language with features to support functional programming style
• https://github.com/sfermigier/awesome-functional-python
• https://old.reddit.com/r/functional_python/