python realize the idea of a computer

Calculator # 
# first get a string 
# to space 
# is no space string 
# the first count innermost parentheses: Find brackets, parentheses and brackets are no other 
# get a expressions without parentheses: only addition and subtraction multiplication and division 
# left to right to locate the first multiplication and division: cycle # 
    symbol number # of the first multiplication and division are not necessarily matched 
    # multiplication and division to find out how to calculate it: 
        # determines a multiplication or division to 
        # If multiplications to '*' content is obtained by dividing the number of string data type 
        # If the division is to use '/' is divided content string data type number 
        after the data type in accordance with rotation # '*', '/' calculation 
        # results replace the original string contents 
# all multiplication and division are done 
# calculated addition and subtraction - addition and subtraction 
    # + + - - + + - should be treated in advance 
    # calculation process all the numbers are calculated as a floating point number 
    # the first can be negative 
# is only one number on the can end