def create_button_code(at: int = 0, home: int = 0, joystick: int = 0, zero_halt: int = 0) -> int:
    assert at in range(4), "Must be in the range 0-3."
    assert home in range(4), "Must be in the range 0-3."
    assert joystick in range(4), "Must be in the range 0-3."
    assert zero_halt == 0 or zero_halt == 1, "Must be 0 or 1."

    button_code = 0

    # bit masks
    BITMASK_AT   = 0x03 # 00000011
    BITMASK_HOME = 0x0C # 00001100
    BITMASK_JS   = 0x30 # 00110000
    BITMASK_ZERO = 0xC0 # 11000000

    # set bits
    button_code &= ~BITMASK_AT
    button_code |= at & BITMASK_AT

    button_code &= ~BITMASK_HOME
    button_code |= (home << 2) & BITMASK_HOME

    button_code &= ~BITMASK_JS
    button_code |= (joystick << 4) & BITMASK_JS

    button_code &= ~BITMASK_ZERO
    button_code |= (zero_halt << 6) & BITMASK_ZERO

    return button_code

def main():
    button_code = create_button_code(at=1, home=1)
    print(button_code)
    # prints 5
    
if __name__ == "__main__":
    main()