As is often the case in Python, you don't actually have to muck about with indices at all to do this.
First, here is a simple solution using your existing data structure. Iterate over mix, and append each item to the appropriate list, depending on whether it's in possibilities or not. (This is the same idea presented in this answer to "How to split a list based on a condition?")
mix = [
[1, 'Blue'],
[2, 'Black'],
[3, 'Black'],
[4, 'Red'],
]
possibilities = [
[1, 'Black'], [1, 'Red'], [1, 'Blue'], [1, 'Yellow'],
[2, 'Green'], [2, 'Black'],
[3, 'Black'], [3, 'Pink'],
[4, 'White'], [4, 'Blue'], [4, 'Yellow'],
[5, 'Purple'], [5, 'Blue'],
]
correct_guesses = []
bad_guesses = []
for item in mix:
if item in possibilities:
correct_guesses.append(item)
else:
bad_guesses.append(item)
print(correct_guesses)
print(bad_guesses)
Output:
[[1, 'Blue'], [2, 'Black'], [3, 'Black']]
[[4, 'Red']]
However, this does a lot of unnecessary looping. Each time you check item in possibilities, the code has to iterate over possibilities (which is a list) to see whether or not item is there.
As others have commented, the issue here is your data structure. Instead of a list, possibilities could be a dictionary. Checking whether a dictionary has a given key, or accessing the value associated with a given key, is O(n); essentially it's "instant" instead of having to go look for it.
possibilities = {
1: ['Black', 'Red', 'Blue', 'Yellow'],
2: ['Green', 'Black'],
3: ['Black', 'Pink'],
4: ['White', 'Blue', 'Yellow'],
5: ['Purple', 'Blue']
}
Here each key is an integer, and each value is a list of the colors that number allows. Then your for loop would look like this, checking if the color is one allowed for that number
for item in mix:
number, color = item
if color in possibilities[number]:
correct_guesses.append(item)
else:
bad_guesses.append(item)
Do you see the problem, though? We're still doing the same thing: using in on a list. We could turn each of those lists into a set instead, which can much more efficiently check whether or not it contains something:
possibilities = {
1: {'Black', 'Red', 'Blue', 'Yellow'},
2: {'Green', 'Black'},
3: {'Black', 'Pink'},
4: {'White', 'Blue', 'Yellow'},
5: {'Purple', 'Blue'}
}
The for loop would remain the same.
With all that in mind, here's a complete solution. I've also changed the two-item lists to tuples, which serves no functional difference in this case, but is more idiomatic.
mix = [
(1, 'Blue'),
(2, 'Black'),
(3, 'Black'),
(4, 'Red'),
]
possibilities = {
1: {'Black', 'Red', 'Blue', 'Yellow'},
2: {'Green', 'Black'},
3: {'Black', 'Pink'},
4: {'White', 'Blue', 'Yellow'},
5: {'Purple', 'Blue'}
}
correct_guesses = []
bad_guesses = []
for item in mix:
number, color = item
if color in possibilities[number]:
correct_guesses.append(item)
else:
bad_guesses.append(item)
print(correct_guesses)
print(bad_guesses)
Output:
[(1, 'Blue'), (2, 'Black'), (3, 'Black')]
[(4, 'Red')]
P.S. Ideally you'd change how you generate possibilities in the first place, but if you're faced with a situation where you have the lists of lists, and want to convert it into the corresponding dictionary of sets, this would work:
possibilities_list = [
[1, 'Black'], [1, 'Red'], [1, 'Blue'], [1, 'Yellow'],
[2, 'Green'], [2, 'Black'],
[3, 'Black'], [3, 'Pink'],
[4, 'White'], [4, 'Blue'], [4, 'Yellow'],
[5, 'Purple'], [5, 'Blue'],
]
possibilities_dict = {}
for num, color in possibilities_list:
if num in possibilities_dict:
possibilities_dict[num].add(color)
else:
possibilities_dict[num] = {color}
Or using defaultdict to simplify the logic:
from collections import defaultdict
possibilities_dict = defaultdict(set)
for num, color in possibilities_list:
possibilities_dict[num].add(color)
