def base_convert(number, fromBase, toBase):
    try:
        # Convert number to base 10
        base10 = int(number, fromBase)
    except ValueError:
        raise
        
    if toBase < 2 or toBase > 36:
        raise NotImplementedError
        
    output_value = ''
    digits = "0123456789abcdefghijklmnopqrstuvwxyz"
    sign = ''
    
    if base10 == 0:
        return '0'
    elif base10 < 0:
        sign = '-'
        base10 = -base10
    
    # Convert to base toBase    
    s = ''
    while base10 != 0:
        r = base10 % toBase
        r = int(r)
        s = digits[r] + s
        base10 //= toBase
        
    output_value = sign + s
    return output_value