Rounding a number to nearest even

[Gerard Flanagan]

On Apr 11, 12:14 pm, bdsatish <bdsat... at gmail.com> wrote:
> The built-in function round( ) will always "round up", that is 1.5 is
> rounded to 2.0 and 2.5 is rounded to 3.0.
>
> If I want to round to the nearest even, that is
>
> my_round(1.5) = 2        # As expected
> my_round(2.5) = 2        # Not 3, which is an odd num
>
> I'm interested in rounding numbers of the form "x.5" depending upon
> whether x is odd or even. Any idea about how to implement it ?

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def myround(x):
    n = int(x)
    if abs(x - n) == 0.5:
        if n % 2:
            #it's odd
            return n + 1 - 2 * int(n<0)
        else:
            return n
    else:
        return round(x)

assert myround(3.2) == 3
assert myround(3.6) == 4
assert myround(3.5) == 4
assert myround(2.5) == 2
assert myround(-0.5) == 0.0
assert myround(-1.5) == -2.0
assert myround(-1.3) == -1.0
assert myround(-1.8) == -2
assert myround(-2.5) ==  -2.0
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