Conversation

Notices

1. Embed this notice
   Greg Wilson (gvwilson@mastodon.social)'s status on Friday, 23-Aug-2024 22:34:08 JST Greg Wilson

   This just in from the Ministry of Subtle Bugs:

   def f():
   print("false")
   return False

   result = all(func() for func in [f, f, f])
   print("just comprehension", result)

   only prints 'false' once before printing "just comprehension", but

   result = all(list(func() for func in [f, f, f]))
   print("with list", result)

   prints 'false' three times before printing "with list". I understand why, but damn, this one was hard to spot.

   • Embed this notice
     powersoffour (powersoffour@mastodon.social)'s status on Friday, 23-Aug-2024 22:34:06 JST powersoffour

     in reply to

     • Warrick Ball

     @warrickball @gvwilson So I'm generally not in favor of being pedantic, but can I ask a clarifying question -- is it that it's short-circuiting, or that the objects are being defined/instantiated at different stages in the execution? I read this as being similar-in-spirit to the (common?) mistake of putting a mutable as a default argument in a function.

   • Embed this notice
     Warrick Ball (warrickball@mas.to)'s status on Friday, 23-Aug-2024 22:34:07 JST Warrick Ball

     in reply to

     @gvwilson

     Because Python is a short-circuiting language, right? I've seen Python coders get tripped up by languages that don't short circuit or, even more confusingly, where it depends on the compiler.

     When I'm inspecting code with people and notice a short circuit, I always try to point it out, even when it isn't relevant to why we're inspecting the code.

   • Embed this notice
     powersoffour (powersoffour@mastodon.social)'s status on Friday, 23-Aug-2024 23:14:32 JST powersoffour

     in reply to

     • Warrick Ball

     @warrickball

   • Embed this notice
     Warrick Ball (warrickball@mas.to)'s status on Friday, 23-Aug-2024 23:14:33 JST Warrick Ball

     in reply to

     • powersoffour

     @powersoffour @gvwilson

     Oh, I'm not actually sure. I'm hoping I'm about to learn something and would be interested to see a longer breakdown...