Why is a `for` loop so much faster to count True values?

Question

I recently answered a question on a sister site which asked for a function that counts all even digits of a number. One of the other answers contained two functions (which t

Answer 1

@MarkusMeskanen's answer has the right bits – function calls are slow, and both genexprs and listcomps are basically function calls.

Anyway, to be pragmatic:

Using str.count(c) is faster, and this related answer of mine about strpbrk() in Python could make things faster still.

def count_even_digits_spyr03_count(n):
    s = str(n)
    return sum(s.count(c) for c in "02468")


def count_even_digits_spyr03_count_unrolled(n):
    s = str(n)
    return s.count("0") + s.count("2") + s.count("4") + s.count("6") + s.count("8")

Results:

string length: 502
count_even_digits_spyr03_list 0.04157966522
count_even_digits_spyr03_sum 0.05678154459
count_even_digits_spyr03_for 0.036128606150000006
count_even_digits_spyr03_count 0.010441866129999991
count_even_digits_spyr03_count_unrolled 0.009662931009999999