Computer Science 111, Fall 2006

Lab #4

September 28, 2006

The purpose of today's lab is to try out some string functions, and work with decision structures.

Get a copy of the file lab4.pyc from my handout directory (with the command getcopy lab4.pyc)
- and then run this program by invoking the python interpreter, and typing import lab4 and then lab4.main().
This is the program that you will write for the this lab

Use emacs to write your own version of the program. This is not a deep, meaningful program. It's just a way to try out some of python's functions and statements.
I have broken it into three parts. Get each part to work first before moving on the the next part.
Here is what your program should do:

Part 1.

Set up a list of six or more strings at the beginning of the main() function definition, that are stored in a variable called canned.
Print a brief introduction on the screen.
Get the user's input: print out a conversational message to the user and read in what the user types. The user should not have to put double quotes around her response.
Use the split() function from the string module and split the user input into a sequence of words. Call the new sequence user_words. (Don't forget to put import string at the top of your file.
print out each word from user_words on a separate line, using a for loop. This kind of loop is useful to separately examine each word in a string.
Make a new empty string called computer, by using the statement
computer = ""
For now, just concatenate, using the string concatenate operator (+), each word from user_words onto variable computer. You will again use a for loop. Print the string stored in the variable computer to verify that the original sentence is reproduced.
Now use a for loop to print every string in the list of strings stored in variable canned, one string per line, and then print 2 blank lines after that.
Finally for the part, print the string
```
We just demonstrated some string manipulations
```
Get all of this part to work before moving to Part 2.

Part 2.

Ask the user to enter the number of pairs of interactions, and place the value in a variable. Make sure the value is an integer type, not a string type value.
Using a definite (for) loop, print one of the canned responses as a prompt, to which the user will respond. Place the user's response in a variable called message. You will pick a canned response randomly. To use python's randrange() function, type
import random before the beginning of the def main() (up where you also have placed import string

Then, once in the body of the loop, if you want a random number between n and m-1, type
random.randrange(n,m). The limits work like the range() function limits. But just one value will be generated, and it is an int, with a value between n and (m-1), inclusive. Use
```
len(canned)
```
as the second parameter. What is the first parameter? Think of the possible index values of a list.
Your program will answer in one of two ways. First, it will
- modify the string by adding a word at the beginning and adding a question mark at the end. It will then use this modified message to input the next user string.
- The next answer to the user's input is just another canned response, as described before.

Part 3. Now try out the if statment
Type the following statements at the end of your lab4.py main() function definition:

    computer = ""
    for word in message:
        old_word = word
        word = string.replace(word,"I","You")
        if old_word==word:
            word = string.replace(word, "You", "I")
        computer = computer + word + " " 
     print computer

This code takes each word from the sequence user_words, and first places the word in a variable called old_word, for safe-keeping.
The statement

        word = string.replace(word,"I","You")

finds all occurrences of the string "I" in word, and replaces it with "You". The variable word will only contain one word so it is either replaced or not. It then assigns the resulting string to the variable word. The next line is the beginning of an if statement

        if old_word==word:

it checks if old_word and word are the same using the equality operator (==). This is a nice feature of python. If they are the same, then no replacement happened. In that case, we want to try

            word = string.replace(word, "You", "I")

and if the word contains "You", we'll replace it with "I" and assign the new string to word.

After this statement, but still in the for loop, concatenate the string in variable word to variable computer, with the string " ", as before. After the loop statement, print out the string contained in the variable computer.