How to take the nth digit of a number in python

You can do it with integer division and remainder methods

def get_digit(number, n):
    return number // 10**n % 10

get_digit(987654321, 0)
# 1

get_digit(987654321, 5)
# 6

The // performs integer division by a power of ten to move the digit to the ones position, then the % gets the remainder after division by 10. Note that the numbering in this scheme uses zero-indexing and starts from the right side of the number.

First treat the number like a string

number = 9876543210
number = str(number)

Then to get the first digit:

number[0]

The fourth digit:

number[3]

EDIT:

This will return the digit as a character, not as a number. To convert it back use:

int(number[0])

I would recommend adding a boolean check for the magnitude of the number. I'm converting a high milliseconds value to datetime. I have numbers from 2 to 200,000,200 so 0 is a valid output. The function as @Chris Mueller has it will return 0 even if number is smaller than 10**n.

def get_digit(number, n):
    return number // 10**n % 10

get_digit(4231, 5)
# 0

---

def get_digit(number, n):
    if number - 10**n < 0:
        return False
    return number // 10**n % 10

get_digit(4321, 5)
# False

---

You do have to be careful when checking the boolean state of this return value. To allow 0 as a valid return value, you cannot just use if get_digit:. You have to use if get_digit is False: to keep 0 from behaving as a false value.

I was curious about the relative speed of the two popular approaches - casting to string and using modular arithmetic - so I profiled them and was surprised to see how close they were in terms of performance.

(My use-case was slightly different, I wanted to get all digits in the number.)

The string approach gave:

         10000002 function calls in 1.113 seconds

   Ordered by: cumulative time

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
 10000000    1.113    0.000    1.113    0.000 sandbox.py:1(get_digits_str)
        1    0.000    0.000    0.000    0.000 cProfile.py:133(__exit__)
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}

While the modular arithmetic approach gave:

         10000002 function calls in 1.102 seconds

   Ordered by: cumulative time

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
 10000000    1.102    0.000    1.102    0.000 sandbox.py:6(get_digits_mod)
        1    0.000    0.000    0.000    0.000 cProfile.py:133(__exit__)
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}

There were 10^7 tests run with a max number size less than 10^28.

Code used for reference:

def get_digits_str(num):
    for n_str in str(num):
        yield int(n_str)


def get_digits_mod(num, radix=10):

    remaining = num
    yield remaining % radix

    while remaining := remaining // radix:
        yield remaining % radix


if __name__ == '__main__':

    import cProfile
    import random

    random_inputs = [random.randrange(0, 10000000000000000000000000000) for _ in range(10000000)]

    with cProfile.Profile() as str_profiler:
        for rand_num in random_inputs:
            get_digits_str(rand_num)

    str_profiler.print_stats(sort='cumtime')

    with cProfile.Profile() as mod_profiler:
        for rand_num in random_inputs:
            get_digits_mod(rand_num)

    mod_profiler.print_stats(sort='cumtime')