CPSC120B
Fundamentals of Computer Science I

Lab 19

Strings

Write a function called append_exclamation(a_phrase), which takes a string as a parameter. This function should return a string, which is simply a_phrase with an exclamation point appended to the end. 















  

    Write a function called get_extents(a_phrase), which
    takes a string as a parameter.  This function should return a
    string, which contains only the first and last characters
    from a_phrase.
  

  


  

  

        
  

  





Password Generation



  Passwords are possibly the most important way that individuals can
  ensure their own safety on the Internet.  However, it is also
  typically the easiest thing for a hacker to figure out, or to get
  their hands on.  This is simply because most Internet users choose
  incredibly weak passwords.  The easiest way to get around this issue
  to to use a randomly generated password.




Details



  Write a function called generate_password(size), which
  takes a positive integers as a parameter.  Your program should
  return a string of lower case letters of the specified size.  This
  function should randomly choose the lower case letters in the
  returned string.





  Your program should ask the user for a password length, and print to
  the terminal the password you generate.





  Make sure you test your program well.  How many test cases do you
  need?  Make sure you follow all of the course's coding conventions.




Example Execution


$ python3 password_generation.py
How long do you want your password? 5
neolp
$ python3 password_generation.py
How long do you want your password? 10
wigmnhgqwn




Hint



  
  

    
    
      
  • 
	
    
	  Since you only need to generate lower case passwords, you
	  can use the string.ascii_lowercase constant to
	  access letters from that range.
	
    
      
    • 
      
  • 
	
    
	  You can use the random module to generate
	  random numbers.  Since we know we are generating lower-case
	  characters, you need to generate a random number to use as
	  an index in the
	  string.ascii_lowercase string.
	
    
      
    • 
      
  • 
	
    
	  Since you know how many characters you want,
	  you should use a for loop for this
	  activity.  You are also using the accumulator pattern again,
	  but with strings this time.
	
    
      
    • 
  








Challenge



  Even random strings of lowercase characters are pretty easy to
  break.  A better program would randomly decide to include some
  uppercase letters as well.  Alter your function so that it will
  sometimes include uppercase letters in the generated passwords.
  Make sure the parameter used to determine how often an uppercase
  character is used is well documented and easily altered.





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. 
  




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.