simplest way to convert either a float or an int to the nearest integer in Python

Question

I want to define a function that can take either an integer or a floating-point number as an argument, and return the nearest integer (ie the input argument itself if it is already an integer). I tried this:

 def toNearestInt(x):
    return int(x+0.5)

but it doesn't work for negative integers.

>>> toNearestInt(3)
3
>>> toNearestInt(3.0)
3
>>> toNearestInt(3.49)
3
>>> toNearestInt(3.50)
4
>>> toNearestInt(-3)
-2

How can I fix it?

Answer 1

Python already has a builtin for this (more or less).

>>> round(-3, 0)
-3.0
>>> round(-3.5, 0)
-4.0
>>> round(-3.4, 0)
-3.0
>>> round(-4.5, 0)
-5.0
>>> round(4.5, 0)
5.0

Of course, you might want to wrap that in a call to int ...

def toNearestInt(x):
    return int(round(x, 0))

Answer 2

You could keep your initial approach here and just check to see if the input is negative and add -0.5 in that case.

def toNearestInt(x):
    a = 0.5
    if x < 0:
        a*=-1
    return int(x+a)