Round integers to the nearest 10

Question

I am trying to round integers in python. I looked at the built-in round() function but it seems that that rounds floats.

My goal is to round integers to the closest

Answer 1

This function will round either be order of magnitude (right to left) or by digits the same way that format treats floating point decimal places (left to right:

def intround(n, p):
    ''' rounds an intger. if "p"<0, p is a exponent of 10; if p>0, left to right digits '''
    if p==0: return n
    if p>0:  
        ln=len(str(n))  
        p=p-ln+1 if n<0 else p-ln
    return (n + 5 * 10**(-p-1)) // 10**-p * 10**-p

>>> tgt=5555555
>>> d=2
>>> print('\t{} rounded to {} places:\n\t{} right to left \n\t{} left to right'.format(
        tgt,d,intround(tgt,-d), intround(tgt,d))) 

Prints

5555555 rounded to 2 places:
5555600 right to left 
5600000 left to right

You can also use Decimal class:

import decimal
import sys

def ri(i, prec=6):
    ic=long if sys.version_info.major<3 else int
    with decimal.localcontext() as lct:
        if prec>0:
            lct.prec=prec
        else:
            lct.prec=len(str(decimal.Decimal(i)))+prec  
        n=ic(decimal.Decimal(i)+decimal.Decimal('0'))
    return n

On Python 3 you can reliably use round with negative places and get a rounded integer:

def intround2(n, p):
    ''' will fail with larger floating point numbers on Py2 and require a cast to an int '''
    if p>0:
        return round(n, p-len(str(n))+1)
    else:
        return round(n, p)    

On Python 2, round will fail to return a proper rounder integer on larger numbers because round always returns a float:

>>> round(2**34, -5)
17179900000.0                     # OK
>>> round(2**64, -5)
1.84467440737096e+19              # wrong 

The other 2 functions work on Python 2 and 3