Round to 5 (or other number) in Python

I don't know of a standard function in Python, but this works for me:

Python 3

def myround(x, base=5):    return base * round(x/base)

It is easy to see why the above works. You want to make sure that your number divided by 5 is an integer, correctly rounded. So, we first do exactly that (round(x/5)), and then since we divided by 5, we multiply by 5 as well.

I made the function more generic by giving it a base parameter, defaulting to 5.

Python 2

In Python 2, float(x) would be needed to ensure that / does floating-point division, and a final conversion to int is needed because round() returns a floating-point value in Python 2.

def myround(x, base=5):    return int(base * round(float(x)/base))

For rounding to non-integer values, such as 0.05:

def myround(x, prec=2, base=.05):  return round(base * round(float(x)/base),prec)

I found this useful since I could just do a search and replace in my code to change "round(" to "myround(", without having to change the parameter values.

It's just a matter of scaling

>>> a=[10,11,12,13,14,15,16,17,18,19,20]>>> for b in a:...     int(round(b/5.0)*5.0)... 1010101515151515202020