[tlocke]

Someone else has mentioned it, but I would have gone with:

  sum(1 for age in ages if age > 17)

with the other method you're treating a boolean as an int. Weak typing.

[palotasb]

bool is explicitly documented to be a subclass of int [1][2], so while it might be an obscure feature, or subjectively not someone's preferred style, I don't see any typing related issue. In general I don't think that treating an object as if it were an instance of one of its base classes is weak typing.

[1]: https://docs.python.org/3/library/functions.html?highlight=s...

[2]: https://docs.python.org/3/library/stdtypes.html#boolean-valu...

[tlocke]

I'd argue that even though it's well defined behaviour in Python, it still appears to me as a programmer as weak typing. For example, Python lets me write:

  if 23:
      print('hello')

and it'll print 'hello'. But I'd prefer a strongly typed approach where this code would give an error saying, 'a bool is expected here'. Sure it's a subjective thing, and this is just my preference.

[dragonwriter]

Its not weak typeing, bools are ints.

“I don’t know the type hierarchy used in language X” is not the same thing as “language X is weakly typed”.

  Python 3.11.4 (tags/v3.11.4:d2340ef, Jun  7 2023, 05:45:37) [MSC v.1934 64 bit 
  (AMD64)] on win32
  Type "help", "copyright", "credits" or "license" for more information.
  >>> isinstance(True, int)
  True
  >>> isinstance(False, int)
  True
  >>> issubclass(bool, int)
  True

[pxeger1]

Bools are ints, but I'd say that makes Python weakly typed (ish - it's a spectrum obviously). Are you just using "weak typing" to mean "implicit type coercion"?

[psd1]

I agree with the improvement in readability but still like the bool/int equivalence:

    sum(int(age > 17) for age in ages)

Every nanosecond is vital!

[tlocke]

Interesting, so I did a little test:

  python -m timeit 'sum(1 for age in range(100000) if age > 17)'
  50 loops, best of 5: 5.08 msec per loop

  python -m timeit 'sum(int(age > 17) for age in range(100000))'
  50 loops, best of 5: 7.96 msec per loop

  python -m timeit 'sum(age > 17 for age in range(100000))'
  50 loops, best of 5: 4.78 msec per loop

[masklinn]

Yep, in python function calls are not cheap, you’re usually better off avoiding them in tight loops.

Plus here on each iteration `int` has to be loaded from the globals before it can be called.