Re: not understanding the result of functools.reduce

[email protected] (Stefan Ram) writes:

> Ethan Carter <[email protected]> wrote or quoted:
>>## The question is how to write such an operator.  I wrote this one:
>>def op(x, b):
>>  return isinstance(x, int) or b
>
>   The main snag with your op function and how you're using
>   reduce is the switch-up in the argument order that "reduce"
>   expects versus how you set up op.
>
>   "functools.reduce" calls the reducer function "op" with two
>   arguments: the accumulated value so far first, then the
>   next element from the iterable.
>
>   You wrote "op" as "op(x, b)", where you treat "x" like an element
>   and "b" like a boolean accumulator, but actually "reduce" hands
>   the accumulator first, then the element.
>
>   So when "reduce" runs, the first argument "x" is actually the boolean
>   accumulator, and the second "b" is the next element.

You're a master.  That happens to be the one thing I didn't check!  I
couldn't think of it, even though I'm well aware that not every binary
operator is commutative.  Such is life!  Thanks so much!