Python Forum

I have to do something with all combinations in a list.

Initial thought
itertools.combinations(mylist, 2)

But I have to something with the values of mylist and computing them over and over seems not logical.

def myfunct(a)
	#do something with a
	#return something

mylist = [1,2,3,4,5]

for index, item in enumerate(mylist):
	val = myfunct(item)
	for i in mylist[index+1:]:
		# do something with 'val' and with i

so in my example I only have to calculate 'val' once for each loop

my thought is doing this with itertools I have to calculate val for each item everytime.


Brainfart or could I do this better?

If the items in mylist are hashable, you could use functools.lru_cache

from functools import lru_cache
import itertools as itt

def myfunct(a):
    #do something with a
    #return something
    print('myfunct({})'.format(a))

myf = lru_cache()(myfunct)
 
mylist = [1,2,3,4,5]

for x, y in itt.combinations(mylist, 2):
    val = myf(x)
    print(x, y)
myf.cache_clear()

Output:
myfunct(1)
1 2
1 3
1 4
1 5
myfunct(2)
2 3
2 4
2 5
myfunct(3)
3 4
3 5
myfunct(4)
4 5