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know the features of your language (lemmy.world)

submitted 9 months ago by jroid8 to c/[email protected]

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[–] [email protected] 21 points 9 months ago (3 children)

Python:

return a or b

i like it because it reads like a sentence so it somewhat makes sense

and you can make it more comprehensive if you want to:

return a if a is not None else b

[–] [email protected] 15 points 9 months ago* (last edited 9 months ago)

This diverges from the OP code snippets if a has the value False.

[–] alehc 7 points 9 months ago (2 children)

I personally dislike this because when you read "or" you expect some boolean result not a random object :/

[–] [email protected] 4 points 9 months ago

there's always the second option for you

[–] [email protected] 1 points 9 months ago* (last edited 9 months ago)

In python: Not necessarily.

If you have an arg whose default is something you’re not supposed to bind as a default value in the function sig (e.g. the result of a function call), make it an Optional, default it to None, and then on the first line just do some_arg = some_arg or interesting_function()

[–] [email protected] 1 points 9 months ago (1 children)

For newer python people, they see return a or b and typically think it returns a boolean if either is True. Nope. Returns a if a is truthy and then checks if b is truthy. If neither are truthy, it returns b.

[–] [email protected] 7 points 9 months ago* (last edited 9 months ago) (1 children)

Returns a if a is truthy and then checks if b is truthy. If neither are truthy, it returns b.

Not quite. If a is not truthy, then the expression a or b will always return b.

So, there is never any reason to check the truthiness of b.

you can paste this in your repl to confirm it does not.

class C:
 def __repr__(self): return [k for k, v in globals().items() if v is self][0]
 def __bool__(self):
  print(f"{self}.__bool__() was called")
  return False

a, b = C(), C()
print(f"result: {a or b}")

spoiler output

a.__bool__() was called
result: b

:::

[–] [email protected] 3 points 9 months ago

Ah, good catch.