CSC111 Lab 4 2015

--D. Thiebaut (talk) 17:39, 14 February 2015 (EST)

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Preparation for Homework #5

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String Slices

• Use Python in interactive mode and try the following Python statements. Try to figure out the answers to the questions.

Python 2.6 (r26:66714, Nov  3 2009, 17:33:38) 
[GCC 4.4.1 20090725 (Red Hat 4.4.1-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> a = "H:/English103/paper1.doc"
>>> a

>>> len( a )

>>> a[0]

>>> a[2]

>>> a[-1]

>>> a[-2]

>>> a[0 : 2]

>>> a[3 : 13]

>>> a[-3 : -1]

>>> a[-5 : -1]

>>> a[-5 : ]                  (no, I didn't forget the second number!)

>>> a[ : 3]                   (and no again, I didn't forget the first number!)

>>> a[3 : -3]

>>> b = "C:/My Documents/paper2.htm"

You will have discovered that both a and b contain strings representing the name of files in a computer. < br />

Challenge #1

• What is the string slice that will return the drive information for a (i.e. 'H:')? If you slice b the same way, do you get the drive information as well? replace a by b, does your statement still return the drive for b?

Challenge #2

• What is the slice that will return the extension only of a (i.e. doc)? What is the slice that will return the extension for b?

Challenge #3

• Once you have figured out the answers to Question 2, write a simple Python program that asks the user for a file name, such as the ones we used for a or b above, and that prints out the same file name back, but with the extension replaced with "txt".

Example

Filename? C:/My Documents/paper02182010.doc

C:/My Documents/paper02182010.txt

Challenge #4

• Write a program that asks the user for her first name and her last name, and outputs a computer account name, that is made of the first letter of first name, plus the last name. (We won't worry about whether we have upper- or lower-case in the output.)

Example

First name? Allie

Last name? Baba

Your computer account name is: ABaba

String Methods

We have already seen several of these methods. This lab is to reinforce our knowledge of strings.

The methods are all documented at this page: http://docs.python.org/lib/string-methods.html. Open this page and refer to it while you are working on this lab.

Use the python shell to test out different string methods:

center()

One of the string methods is the center function.

Use it to center the title "computer SCIENCE 111" between two lines of 45 dashes. Use a variable called myTitle to store the string.

myTitle = "computer SCIENCE 111"
print( 45*"-" )
print( myTitle.center( 45 ) )
print( 45*"-" )

< br />

capitalize()

< br /> Instead of printing the variable myTitle, print myTitle.capitalize( ) and see what happens. < br />

upper()

< br /> Use upper() instead of capitalize(). Observe the new output. < br />

title()

< br /> Same exercise, but with the title() method. < br />

Challenge #1

• Write some Python code that will ask for your name, then your last name, and will print both of them centered between two lines of 60 dashes. Make your program capitalize the first letter of each word.

Example

 your first name? alexAndra
 your last name?  SMITH
 
 ------------------------------------------------------------
                       Alexandra Smith                       
 ------------------------------------------------------------

Replacing substrings in a string

To replace a substring of a string (or a word in a sentence), all you need to do is to use the replace() method.

    # we define a multi-line string with triple-double-quotes
    sentence = """Strength is the capacity to break a chocolate 
               bar into four pieces with your bare hands - and 
               then eat just one of the pieces"""
 
    # display original string
    print( "Original sentence =", sentence )

    # replace chocolate by carrot
    sentence = sentence.replace( "chocolate", "carrot" )

    # display resulting string
    print( "New sentence = ", sentence )

Try it and replace the word "piece" by the word "chunk" in the same sentence, so that now you're breaking carrots into chunks.

Multiple Replacements

We are still dealing with the sentence above, but we want to replace four separate words by four new words. The words we want to replace are in this list:

toBeReplaced = ["chocolate", "piece", "hand", "break"]

and the replacement words are in this list:

   newWords = [ "carrot", "chunk", "elbow", "melt" ]

Write python statements that will take the string sentence and replace chocolate by carrot, then it will look for piece and replace it by chunk, hand by elbow, and break by melt.

Use a for-loop!

Count()

Read the documentation on the method count() and write some statements that output the number of times the word "piece" appears in sentence using the count() method.

Strip()

Read the documentation about the method strip() and use it to allow you to print the lines below left aligned.

listOfStrings = [ "          But then, shall I never get any older than I am now?      ",
                        "     That'll be a comfort, one way -- never to be an old woman --          ",
                        "          but then -- always to have lessons to learn!           ",
                        "    Alice    " ]

Splitting strings

First, read the documentation on the split() method.

Let's use the same string as before.

    sentence = """Strength is the capacity to break a chocolate 
               bar into four pieces with your bare hands - and
               then eat just one of the pieces"""

And process it that way

  
list1 = sentence.split( "\n" )
print( "list1 = ", list1 )

list2 = sentence.split( )
print( "list2 = ", list2 )
 
list3 = sentence.split( 's' )
print( "list3 = ", list3 )

Programming Question 2

Make your program print the number of words in sentence (there are several ways to do that: one long, one very short).

Programming Question 3

Make your program display the first and last words of the sentence.

Programming Question 4

Assume that you have a string of this type:

   NYTBestSellers = """1. THE HELP, by Kathryn Stockett
                                2. WORST CASE, by James Patterson and Michael Ledwidge
                                3. THE LOST SYMBOL, by Dan Brown
                                4. POOR LITTLE BITCH GIRL, by Jackie Collins
                                5. WINTER GARDEN, by Kristin Hannah """

Write the code that will take this string, process it, and output the information in a different format, shown below:

  Kathryn Stockett                                     The Help
  James Patterson and Michael Ledwidge                 Worst Case
  Dan Brown                                            The Lost Symbol
  Jackie Collins                                       Poor Little Bitch Girl
  Kristin Hannah                                       Winter Garden

For this part of the lab, you want to have your Macs running in Mac OS X mode!

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Solution Programs

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