parse.py

# A simulator for the redstone parser - the first part of the graphing calculator.
# Converts a list of characters (0-9,x,y,z,+,-) to a list of terms (sign, coefficient, x degree, y degree, z degree).

def parse_polynomial(poly):
    terms = []

    # Term state
    sign = 0
    coef = 0
    x_deg = y_deg = z_deg = 0

    # Helper state
    coef_seen = False

    def commit_term():
        nonlocal sign, coef, coef_seen, x_deg, y_deg, z_deg

        terms.append([sign, coef if coef_seen else 1, x_deg, y_deg, z_deg])
        
        sign = 0
        coef = 0
        coef_seen = False
        x_deg = y_deg = z_deg = 0

    for char in poly:

        # Term separator
        if char == '+' or char == '-':
            commit_term()
            sign = 1 if char == '-' else 0

        # Digit (coefficient or exponent)
        elif '0' <= char <= '9':
                coef = coef * 10 + int(char)
                coef_seen = True

        # Variable
        elif char in 'xyz':
            if char == 'x':
                x_deg += 1
            elif char == 'y':
                y_deg += 1
            elif char == 'z':
                z_deg += 1

    # Commit final term
    commit_term()

    return terms


# Example

poly = "3xyzzz-4xyyz-7yxz"
print(parse_polynomial(poly))