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check if all elements in a list are identical

user1517 Published in June 25, 2018, 7:29 pm

I need the following function:

Input: a list


  • True if all elements in the input list evaluate as equal to each other using the standard equality operator;
  • False otherwise.

Performance: of course, I prefer not to incur any unnecessary overhead.

I feel it would be best to:

  • iterate through the list
  • compare adjacent elements
  • and AND all the resulting Boolean values

But I'm not sure what's the most Pythonic way to do that.


Thank you for all the great answers. I rated up several, and it was really hard to choose between @KennyTM and @Ivo van der Wijk solutions.

The lack of short-circuit feature only hurts on a long input (over ~50 elements) that have unequal elements early on. If this occurs often enough (how often depends on how long the lists might be), the short-circuit is required. The best short-circuit algorithm seems to be @KennyTM checkEqual1. It pays, however, a significant cost for this:

  • up to 20x in performance nearly-identical lists
  • up to 2.5x in performance on short lists

If the long inputs with early unequal elements don't happen (or happen sufficiently rarely), short-circuit isn't required. Then, by far the fastest is @Ivo van der Wijk solution.

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