[Python] How do I make an index to combination script closed form in python?

I'm coding in python and I want to make my index to combination script closed form. There is currently a while loop in the script that is making the code lag.

My code so far is:

from math import floor

def index_to_combination(index, min_length=40):
iterable = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789`~!@#$%^&*()-_=+[{]}\\|;:'\",<.>/? "

digits_str = str(iterable) # '123456789'
base = len(digits_str)

result = ''
while True:
q = floor(index / base)
rem = index - base * q
result = digits_str[rem] + result
index = q
if index == 0 and len(result) >= min_length:
break

return result


print(index_to_combination(123456789))


I want to make this closed form by removing the loop. Can someone show me how to do this?

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