gistfile1.py

#!/usr/bin/python
import math

def func(x, prec):
    if (x + 0.5) == round(x + 0.5):
        return x - 0.5
    y = 0
    for i in range(1, prec + 2):
        y += ((-1)**i * math.sin(2 * i * x * math.pi)) / i
    return x + (y / math.pi).real