Fastest way to check for multiple conditions

Question

I am looking to check for 3 conditions, any of which triggers a continue.

The 2 ways I am looking at are 1) if with multiple conditions 2) if and elif

def conditions_1(a,b,c):
    numbers = []
    min_no = min(a,b,c)
    max_no = max(a,b,c)
    for no in range(min_no,max_no+1):
        if no == 0 :
            continue
        elif no + min_no == 0:
            continue
        elif math.gcd(min_no, no)> 1:
            continue
        else:
            numbers.append(no)
    return(numbers)


def conditions_2(a,b,c):
    numbers = []
    min_no = min(a,b,c)
    max_no = max(a,b,c)
    for no in range(min_no,max_no+1):
        if no == 0 or no + min_no == 0 or math.gcd(min_no, no)> 1:
            continue
        else:
            numbers.append(no)
    return(numbers)

for _ in range(10):
    t0 = time.time()
    conditions_1(-5000, 10000, 4)
    t1 = time.time()
    conditions_2(-5000, 10000, 4)
    t2 = time.time()
    if t2-t1 > t1-t0:
        print('2nd')
    else:
        print('1st')

May I know if there is a difference in both ways?

The first probably has a few extra assembly instructions but this isn't going to be a bottleneck — Sayse, Oct 11 '19 at 08:23
In the second function you could use the logical `not` around the whole condition and change the `continue` for the append. It will behave in the same way but be shorter. — Gábor Fekete, Oct 11 '19 at 08:46

GPhilo · Accepted Answer · 2019-10-11T08:46:49.410

Thanks to the fact that or has short-circuit evaluation (i.e., it evaluates the list of conditions left to right and stops at the first True), the execution pattern is the same between your two variants (minus the fact that in the if/elif case you may have multiple jumps when testing each condition).

Coding-style-wise, the second is of course a lot better (no repetition of continue, clearer intent of the if/else block) and should be the way you structure your code.

Side note: Remember that if an expression gets too long, you can put it in parentheses and break it over several lines:

if (some_very_lengthy_condition_1 == my_very_lengthy_name_1 or
    some_very_lengthy_condition_2 == my_very_lengthy_name_2 or
    some_very_lengthy_condition_3 == my_very_lengthy_name_3 ):
  pass # do something

As Gábor noted in the comments, in python you also have the any and all operators, which apply to iterables. any(iterable) is equivalent to oring all values in the iterable, while all(iterable) is equivalent to anding them. Short-circuit logic applies here as well, so that only the minimal number of values in iterable are evaluated when computing the expression result.

I would also mention `any` and `all` as they also short-circuit. Those can be used for _really_ long conditions. — Gábor Fekete, Oct 11 '19 at 08:41

Fastest way to check for multiple conditions

1 Answers1