Choose three different values from list in Python

Question

I have a list of points with their coordinates, looking like this:

[(0,1),(2,3),(7,-1) and so on.]

What is the Pythonic way to iterate over them and choose three different every time? I can't find simpler solution than using three for loops like this:

for point1 in a:
    for point2 in a:
        if not point1 == point2:
        for point3 in a:
            if not point1 == point3 and not point2 == point3:

So I'm asking for help.

Answer 1

import random

lst = [(0, 1), (2, 3), (7, -1), (1, 2), (4, 5)]

random.sample(lst, 3)

This will just give you 3 points chosen at random from the list. It seems you may want something different. Can you clarify?

Answer 2

You can use itertools.combinations :

from itertools import combinations

for point1, point2, point3 in combinations(points, 3):
    ...

Answer 3

Use a set .

Let's assume your initial set of coordinates is unique.

>> uniquechoices=[(0,1),(2,3),(7,-1) and so on.]

Fill a set called selected until it has say 3 values, using random selection

>> from random import randint
>> selected=set([])
>> while len(selected) < 3: selected.add(uniquechoices[randomint(0,len(uniquechoices))])