How to replace many 'if...elif' statements in Python? [duplicate]

Question

I wrote some code with a lot of 'if..elif' statements in Python. I know the code style may be considered bad and I want to improve it.

num = int(input('please input a number: '))

if num <= 0:
    print('1')
elif 0 < num <= 5:
    print('2')
elif 5 < num <= 10:
    print('3')
elif 10 < num <= 15:
    print('4')
elif 15 < num <= 20:
    print('5')
elif 20 < num <= 25:
    print('6')

I would like to know how to replace so many 'if..elif' statements with other solutions?

Answer 1

You could do something like this:

print(((num - 1) // 5) + 2)

Example when num is 20:

((num - 1) // 5) + 2
((20 - 1) // 5) + 2
(19 // 5) + 2
3 + 2
5

In the general case... not sure. If you're talking about a completely arbitrary if-elif-else construct, then I would say no, at least not in a way that would help readability. In fact, the answer I just gave you for your specific example might not even help readability, so I'm not sure how well you can hope for that in the general case.

Answer 2

For simple examples like this where the different cases fit a clear pattern, the best thing would be something like what RedRoboHood suggested where you remove the conditional altogether (modified slightly to support lower bound), e.g.

print('%s' % max((num - 1) // 5 + 2, 1))

If you want to be slightly more general and allow print statements that do not follow a pattern with the input, you could use a python dictionary:

# what to print if num is less than the number but greater than the previous
mapping = {0:'1', 5:'2', 10:'3', 15:'4', 20:'5', 25:'6'}
# clamp the number to the upper bound of the desired range
clamped_num = 5 * max((num - 1) // 5, -1) + 5
print(mapping[clamped_num] if clamped_num in mapping else 'Bad value')

However, there will always be times where you cannot boil it down like this, and for those I think if-else statements are fine.