Polynomial Derivatives

def polyparse(s,x):
        c = []
        current = ['','0','coefficient']
        for i in s:
            if i in ['0','1','2','3','4','5','6','7','8','9','.']:
                if current[2] == 'coefficient':
                    current[0] += i
                elif current[2] == 'exponent':
                    current[1] += i
            elif i == x:
                if current[0] == '':
                    current[0]=1
                elif current[0] == '-':
                    current[0] = -1
                current[2] = 'exponent'
                current[1] = '1'
            elif i == '^':
                current[1] = '0'
            elif i == '+':
                c.append([float(current[0]), int(current[1])])
                current = ['','0','coefficient']
            elif i == '-':
                c.append([float(current[0]), int(current[1])])
                current = ['-','0','coefficient']
        c.append([float(current[0]), int(current[1])])
        return c
def derivative(poly):
    for i in poly:
        i[0] *= i[1]
        i[1] = i[1]-1
    return poly
def polyform(poly,x):
    p = ''
    for i in poly:
    if i[0] == 0:
        continue
        if i[0] >= 0:
                p += '+'
        if i[0] == int(i[0]):
            i[0] = int(i[0])
    if i[0] == 1:
        i[0] = ''
        if i[1]==1:
            p += str(i[0]) + x
        elif i[1]== 0:
            p += str(i[0])
        else:
            p += str(i[0]) +x +'^' +str(i[1])
    p = p[1:]
    return p

while True:
    x = raw_input('Enter your variable: ')[0]
    print 'Derivative: ' + polyform(derivative(polyparse(raw_input('Enter your polynomial: '),x)),x),'\n'