ValueError when iterating through simple list

I am trying (as a newb Pythoneer) to translate an old homework assignment from Java to Python. I am getting a TypeError when I try to iterate through a list. It is claiming that I am not using an integer value for my index, but I can't see how I am not. I've probably included too much code, but just in case the error isn't where I think it is (TypeError is on very last line):

def power(x, y):
    if isinstance(y, int):
        solution = x
        if y == 0:
            return 1
        else:
            for i in range(1,y):
                solution = solution*x
        return solution
    else:
        raise TypeError("Power: Non-Integer power argument")

def factorial(x):
    if isinstance(x, int) and x >= 0:
        if x == 1 or x == 0:
            return 1
        else:
            solution = int(x)
            while x > 1:
                solution = solution*(x-1)
                x -= 1
            return solution
    else:
        raise TypeError("Factorial: argument must be a positive integer")

def abs(x):
    if x < 0:
        x = -x
    return x


# Calculates the coefficients of the
# Taylor series of Sin(x).
# center argument must be 0, pi/4, pi, or 3pi/2
def coef_calc(center):
    coef = [1]*32
    i = int(0)
    c_temp = 1  # temporary holding place for calculated coefficient

    if center in [0, PI/4, PI, 3*PI/2]:

        # Mclauren Series (center = 0)
        if center == 0:
            while c_temp > 1.0e-31:
                c_temp = power(-1, i)/factorial(2*i + 1)
                coef[i] = c_temp
                i += 1
    else:
        raise ValueError("Argument not in [0, pi/4, pi, 3pi/2]")

    return coef


# CONSTANTS
PI = 3.1415926535897932
SQRT_TWO = 1.41421356237309504880

if __name__ == "__main__":
    print(power(4,2))
    print(factorial(4))
    print(abs(-0))

    coef = coef_calc(0)
    for x in coef:
        print(coef[x] + "\n")