CPSC120A
Fundamentals of Computer Science I

Lab 21

String Traversal

Practice 1

Write a function is_substring(word_1, word_2). Your function should use the in operator to determine if the string word_1 is a substring of word_2. word_1 is a substring of word_2 if all of the characters of word_1 exist sequentially inside of word_2. 
















  
Practice 2




  Write a function sum_ord(some_text).  Your
  function should use the for character in word style of
  loop to sum the ordinal values of all of the characters
  in some_text.




  

    
  

  

    
  

  





Reading Level



  Some states require that legal documents not be written above a
  certain grade level. The Flesch-Kincaid grade level is a numeric
  score that indicates the minimum grade level in which an average
  student would be able to understand a text. Writing a function that
  computes the grade level of text requires being able to count the
  number of occurrences of certain characters.




Details



  In a file called reading_level.py write the
  function compute_reading_level(text).  The function
  should return the Flesch-Kincaid grade level of the input text.  The
  Flesch-Kincaid grade level equation requires determining the number
  of syllables in a sentence, which is very difficult for a program to
  compute without a dictionary. The following equation is an
  approximation to the Flesch-Kincaid grade level that does not use
  syllables:



$$0.39\cdot(W/S)+11.8\cdot((L/3)/W)-15.59$$



  Where \(W\) is the total number of words, \(S\) is the total number
  of sentences, and \(L\) is the total number of letters. Assume that
  all sentences end in a period, that all words are separated by a
  single space, and that all characters that are not a space or period
  are letters.




Sample Test Cases



  
    

      Function Parameters
      Expected Output
    

  
  
    

      'I do not like them Sam I am. I do not like green eggs and ham.'
      -1.4075
    

    

      'To be or not to be that is the question. Whether tis nobler
      in the mind to suffer the slings and arrows of outrageous
      fortune or to take arms against a sea of troubles and by
      opposing end them.'
      7.445769230769233
    

  




Hint



  
  

    
    
      
  • 
	
    
          Determining the number of words requires counting the number
          of space characters and determining the number of sentences
          requires counting the period characters.  Instead of writing
          code to count each of these characters separately,  write a
          function count_character(character, text) that
          counts the number of times character occurs
          in text.  The function should use an
          accumulator variable to count and a for loop to traverse the
          text one character at a time.  For each character in the text
          that is equal to input character, increment the counter.
	
    
      
    • 
      
  • 
	
    
          Use the above function to determine the number of words and
          sentences.  Determine the number of letters by using the
          length of the input text and the number of non-alphabetic
          characters.  Before computing the reading level, test your
          code by printing the number of words, sentences, and letters
          on short examples.
	
    
      
    • 
      
      
      
      
      
      
      
  






  
Challenge

  

    The character count function was easy to write because it assumes
    that the input text only has alphabetic characters, single space
    characters, and period characters.  This isn't very useful because
    most text does not conform to these restrictions.  Modify the
    function so that it can work for any text.  It should:
  

  
    
    
  1. 
      allow any number of space, tab, or new line characters between
      words and sentences.
    
    2. 
    
  2. 
      allow sentences to end in a period, question mark, or
      exclamation point.
    
    3. 
    
  3. 
      ignore all non-alphabetic characters when counting letters.
    
    4. 
  




Caesar



  Most of us like to keep secrets.  For example, I don't want you to
  know my credit card number.  I'd rather you not be able to buy
  things with my money.  However, communication over the Internet is
  like trying to shout in a crowded room.  Everyone can hear what you
  are saying.  So, to protect our valuable secrets, we rely
  on encryption schemes.  Today, you are going to implement a
  simplistic encryption scheme known since Roman times:  Caesar
  cipher.




Details



  In a file called caesar.py write the
  function encrypt_word(a_word).  This function takes a
  single string as a parameter.  Your function should return the
  encryption of the a_word parameter.




  Encryption in the Caesar schema relies on shifting letters in the
  alphabet.  By default, this shift is 3 letters.  So, \(a\) becomes
  \(d\), \(b\) becomes \(e\), etc.  The only issue with this is at the
  end of the alphabet.  The end of the alphabet wraps around to the
  front.  So, \(x\) becomes \(a\), \(y\) becomes \(b\), and \(z\)
  becomes \(c\).




Sample Test Cases



  
    

      Function Parameters
      Expected Output
    

  
  
    

      hello
      -khoor
    

    

      goodbye
      jrrgebh
    

  




Hint



  
  

    
    
      
  • 
	
    
	  The ord function gives you the ASCII
	  representation of a character.  If you subtract
	  the ord('a') from this, you will get the
	  position in alphabet a character is.
	
    
      
    • 
      
  • 
	
    
	  You can use % to make the cyclic property of
	  the algorithm works.  There are 26 letters in our alphabet.
	
    
      
    • 
      
  • 
	
    
	  The chr function takes an integer, and returns
	  to you the character that represents the ASCII value.
	
    
      
    • 
  






  
Challenge

  

    Encryption for Caesar is useful, but in order to talk to anyone
    they need to be able to decrypt the Caesar encryption.  Add a
    function decrypt_word(a_word), which returns the
    decryption of the a_word.
  




Submission


Please show your source code and run your programs for the instructor or lab assistant. Only a programs that have perfect style and flawless functionality will be accepted as complete.