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Opinions on truthiness across languages

Different languages have different opinions about what to treat as “truthy” or “falsy” when using a non-boolean object as an expression inside an if statement.

I looked at Python, Groovy, Javascript and Ruby to compare their differences.

Value Python Groovy Javascript Ruby
null / nil False False False False
Zero (0) False False False True
Empty String (“”) False False False True
Empty list / dict False False True True

My observations and personal opinions on language design:

  • Python treats zero, empty strings and collections all as ‘falsy’. Personally, I find this the most intuitive convention.
    • Treatment of zero and null as falsy has historical precedent, from C.
    • Treatment of empty strings and collections is a nice convenience, given the number of times I’ve written conditionals like if (foo != null and !foo.empty()). It’s usually the exception that I want to distinguish between null and empty in a conditional. So it’s nice that if (foo) handles the common case, then I can write if (not foo is None) when I really do want to distinguish null.
    • Treatment of empty string as similar to null feels familiar from my Oracle experience.
  • Groovy is inspired by Python and adopts similar conventions for truthiness.
  • Ruby takes a different opinion that all values are truthy except nil (and false, of course). While it’s not my personal preference, it’s defensible and self-consistent.
  • Javascript can reliably be expected to deliver a WTF. Javascript treats zero and empty strings as falsy, but empty collections as truthy.
    To me, it’s hard to understand why strings and collections ought to behave differently; the Python behavior makes much more sense. But wait, it gets even better: check out this link on StackOverflow.
Written on May 14, 2017