Interpolate list example

''' Create another list. (iterative) '''
def interpolate1(l):
    if l is not list: l = list(l)
    if len(l) > 2:
    	for i in range(len(l)-1):
            l[i] = (l[i]+l[i+1])/2
    return l[:-1]

''' Create another list. (recursive) '''
def interpolate2(l):
    def execute(l, r, i):
        if len(r) < len(l) - 1:
            r.append((l[i]+l[i+1])/2)
            return execute(l, r, i+1)
        return r
    if len(l) > 2:
    	return execute(l, list(), 0)
    return l

''' Edit copy list in place. (recursive) '''
def interpolate3(l):
    def execute(l, i):
        l[i] = (l[i]+l[i+1])/2
        if i < len(l)-2:
        	return execute(l, i+1)
        return l
    if len(l) > 2:
    	return execute(list(l), 0)[:-1]
    return l

''' baavgai's solution. '''

def interpolate4(l):
    if l is not list: l = list(l)
    if (len(l) < 2):
        return l[:-1] # this is the only return instance we'll ever create
    else:
        n = l.pop(0) # pop
        n2 = l.pop(0) # pop
        l.insert(0, n2) # push the last pop back
        r = interpolate4(l) # all self, now one number taken from top
        r.insert(0, (n+n2)/2) # do the math
        l.insert(0, n) # push the other number back, so we balance
        return r # return the result

def interpolate5(l):
    if len(l) < 2:
        return []
    else:
        result = [(l[0]+l[1])/2]
        result.extend(interpolate5(l[1:]))
        return result

l = (0, 1, 2, 4, 8, 16, 32, 64, 128)

print interpolate1(l)
print interpolate2(l)
print interpolate3(l)
print interpolate4(l)
print interpolate5(l)

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