class Ref(object):
    def __init__(self, value=None):
        self.value = value

def harmonic_sum(i, lo, hi, term):
    # term is passed by-name, and so is i
    temp = 0
    i.value = lo
    while i.value <= hi:  # Python "for" loop creates a distinct which
        temp += term() # would not be shared with the passed "i"
        i.value += 1   # Here the actual passed "i" is incremented.
    return temp

i = Ref()

# note the correspondence between the mathematical notation and the
# call to sum it's almost as good as sum(1/i for i in range(1,101))
print harmonic_sum(i, 1, 100, lambda: 1.0/i.value)