[Tutor] Roman to digital (pseudocode)

Kent Johnson kent37 at tds.net
Wed Mar 14 00:51:40 CET 2007

Alan Gilfoy wrote:
> This, I heard, is more difficult than digital-to-Roman, since you have  
> to "read" the subtractive cases, with a smaller numeral placed before  
> a larger numeral, without simply adding all the numerals' values up
> I'm going to use a raw_input prompt to ask the user which Roman  
> numeral he/she wants to convert. How do I "screen" for inputs that  
> have characters besides "I", "V", "X", "L", "C", "D", or "M"?

You could have a string containing all the allowed characters and make 
sure each input character is in the allowed list.
> Second Python question:
> I know there's a way to "find out" the name of the first item in a list
> (ListName[0]), but is there a way to find out the first character of a string?

Lists and strings are both sequences and many of the same operations 
work on both. (All of the immutable sequence operations work on both.) 
So MyString[0] is the first character in a string.
> Also, is there a way to "ask" Python what characters are before and  
> after the character in the string that you're asking about?
> For example, usign the sample string "MCMXVII" (1917):
> How would you ask Python:
> "What's the 3rd character in this string?" (returns "M")

> "What's before that character?" (returns "C")
s[1] or maybe s[2-1] if the 2 is actually in a variable.


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