I have a problem with randomizing a list with restrictions in Python (3). I have seen a few other questions relating to this, but none of them really seem to solve my problem. I'm a beginner, so any help is much appreciated!

I'm designing an experiment using two types of stimuli: shapes and colors (four of each). I need to generate permutations of all 16 combinations, which I have done with random.shuffle-function:

import random# letters are shapes, numbers are colors
x=["a1","a2","a3","a4","b1","b2","b3","b4","c1","c2","c3","c4","d1","d2","d3","d4"]random.shuffle(x)

So far so good. However, I want to avoid a shape (letter) or color (number) to appear two times in succession in my result (e.g. "a2" followed by "a4", or "c2" followed by "a2").

Is there a way to make such a restriction?
Thanks in advance!

One way to handle this might be to have two lists one of shapes and one of colors. Shuffle each list individually. Now intermix the two lists. Since each list was built randomly, the mixed list is random as well, but you do not have any two entries together.

Note that using zip, you will actually get sets of pairs which will enable you to handle your test by getting each pair from the result.

In this particular case each shape is a member of the list shapes while each color is a member of the list colors

shapes = ['a', 'b', 'c', 'd']
colors = ['1', '2', '3', '4']
zip(shapes, colors)
[('a', '1'), ('b', '2'), ('c', '3'), ('d', '4')]

This gives us each individual shuffle rather than generating all 16 possibilities at once and then shuffling them. This might enable you to generate your test better.

If you want to ensure that two sets of lists do not have the same color or shape in the same position as the previous group of four, then you can test for that after the shuffle against the previous setting.

testing = True
while testing:newcolors = colorsrandom.shuffle(newcolors)# perform the test that you want to make get testresult True or Falseif testresult:colors = newcolorstesting = False

This will keep shuffling until testresult becomes True and discard all invalid results from random.shuffle()