Question

I’m fairly new to Python, and was wondering how would I be able to control the decimal precision of any given number without using any the decimal module or floating points (eg: ” %4f” %n).

Examples (edit):

input(2/7)

0.28571428571….

input(1/3)

0.33333333333333….

and I wanted them to thousand decimal points or any decimal point for that matter. I was thinking of using a while as a controlled loop, but I’m not really sure how to do so. Thanks

edit: The reason why I’m not using the decimal module is just so I can conceptualize the algorithm/logic behind these type of things. Just trying to really understand the logic behind things.

Answer 1

Without the Decimal module (why, though?), assuming Python 3:

def divide(num, den, prec):
    a = (num*10**prec) // den
    s = str(a).zfill(prec+1)
    return s[0:-prec] + "." + s[-prec:]

Thanks to @nneonneo for the clever .zfill() idea!

>>> divide(2,7,1000)
'0.28571428571428571428571428571428571428571428571428571428571428571428571428571
42857142857142857142857142857142857142857142857142857142857142857142857142857142
85714285714285714285714285714285714285714285714285714285714285714285714285714285
71428571428571428571428571428571428571428571428571428571428571428571428571428571
42857142857142857142857142857142857142857142857142857142857142857142857142857142
85714285714285714285714285714285714285714285714285714285714285714285714285714285
71428571428571428571428571428571428571428571428571428571428571428571428571428571
42857142857142857142857142857142857142857142857142857142857142857142857142857142
85714285714285714285714285714285714285714285714285714285714285714285714285714285
71428571428571428571428571428571428571428571428571428571428571428571428571428571
42857142857142857142857142857142857142857142857142857142857142857142857142857142
85714285714285714285714285714285714285714285714285714285714285714285714285714285
7142857142857142857142857142857142857142857'

Caveat: This uses floor division, so divide(2,3,2) will give you 0.66 instead of 0.67.