Getting indices of True values in a boolean list

Question

I have a piece of my code where I'm supposed to create a switchboard. I want to return a list of all the switches that are on. Here "on" will equal True and "off" equal False. So now I just want to return a list of all the True values and their position. This is all I have but it only return the position of the first occurrence of True (this is just a portion of my code):

self.states = [False, False, False, False, True, True, False, True, False, False, False, False, False, False, False, False]  def which_switch(self):     x = [self.states.index(i) for i in self.states if i == True] 

This only returns "4"

Answer 1

Use enumerate, list.index returns the index of first match found.

>>> t = [False, False, False, False, True, True, False, True, False, False, False, False, False, False, False, False] >>> [i for i, x in enumerate(t) if x] [4, 5, 7] 

For huge lists, it'd be better to use itertools.compress:

>>> from itertools import compress >>> list(compress(xrange(len(t)), t)) [4, 5, 7] >>> t = t*1000 >>> %timeit [i for i, x in enumerate(t) if x] 100 loops, best of 3: 2.55 ms per loop >>> %timeit list(compress(xrange(len(t)), t)) 1000 loops, best of 3: 696 µs per loop 

Answer 2

If you have numpy available:

>>> import numpy as np >>> states = [False, False, False, False, True, True, False, True, False, False, False, False, False, False, False, False] >>> np.where(states)[0] array([4, 5, 7])