COMPSCI 101 Principles of Programming

1. COMPSCI 101Principles of Programming Lecture 21 – Complex String Processing

2. Learning outcomes • At the end of this lecture, students should be able to: • Write code using more complex boolean operators • Write code transforming strings COMPSCI 101 - Principles of Programming

3. Review • Strings and Lists are Sequences • Test Cases are Important • Boolean Operators:and, or and not COMPSCI 101 - Principles of Programming

4. Exercise • Write a function named who_wins() that accepts the guesses for person1 and person2 as parameters and determines who wins “Rock Paper Scissors” and returns “person1”, “person2” or “tie” >>> who_wins("rock","scissors") 'person1' >>> who_wins("rock","paper") 'person2' >>> who_wins("paper","paper") 'tie' COMPSCI 101 - Principles of Programming

5. Answer defwho_wins(person1_choice,person2_choice): if (person1_choice == "rock" and person2_choice == "scissors") or (person1_choice == "scissors" and person2_choice == "paper") or (person1_choice == "paper" and person2_choice == "rock"): return "person1" if person1_choice == person2_choice: return "tie" return "person2” COMPSCI 101 - Principles of Programming

6. Exercise • Write a program that calls a function named poetry()that returns random poetry of the form Noun Verb Noun >>> poetry() 'friend loves friend' >>> poetry() 'dog hates cat' COMPSCI 101 - Principles of Programming

7. Answer import random def poetry(): noun1 = random.randint(0,5) verb = random.randint(0,3) noun2 = random.randint(0,5) nouns = ["friend", "dog", "cat", "rabbit", "girl", "boy"] verbs=["loves","hates","likes","is afraid of"] return nouns[noun1] + " " + verbs[verb] + " " + nouns[noun2] poetry() COMPSCI 101 - Principles of Programming

8. Exercise • Write a function named remove_punctuation() that accepts a string containing a written fragment and returns the fragment with all the punctuation removed. >>> remove_punctuation("'I know the answer! The answer lies within the heart of all mankind! The answer is 12? I think I'm in the wrong building.' (Charles Schulz, 'Peanuts')") 'I know the answer The answer lies within the heart of all mankind The answer is 12 I think Im in the wrong building Charles Schulz Peanuts' COMPSCI 101 - Principles of Programming

9. Answer defremove_punctuation(sentences): new_sentences= "" punctuation = ["'", "!", ".", "(", ")", ",", "?", ":", '"'] for character in sentences: if character not in punctuation: new_sentences += character return new_sentences COMPSCI 101 - Principles of Programming

10. Exercise • Write a function namedisogram() that accepts a word as a parameter and returns True if it is an isogram and False otherwise. • An isogram, sometimes known as a nonpattern word, is a word or phrase in which every letter occurs the same number of times. >>> isogram("subdermatoglyphic") True >>> isogram("deed") True >>> isogram("sara") False COMPSCI 101 - Principles of Programming

11. Answer def isogram(word): letter = word[0] num = count(letter,word) for i in range(1,len(word)): if num != count(word[i],word): return False return True def count(letter,word): count = 0 for letter2 in word: if letter == letter2: count = count + 1 return count COMPSCI 101 - Principles of Programming

12. Exercise • Write a function named semordinlap() that accepts a word as a parameter and returns True if it is a semordinlap and False otherwise. • A semordnilapis a word which when reversed is another valid word >>> semordnilap("dog") True >>> semordnilap("dan") False COMPSCI 101 - Principles of Programming

13. Answer defsemordnilap(word): dictionary_file= open("unixdict.txt", "r") dictionary = dictionary_file.read() dictionary_list = dictionary.split() if word in dictionary_list and reverse(word) in dictionary_list: return True return False def reverse(word): new_word = "" for i in range(len(word)-1,-1,-1): new_word += word[i] return new_word COMPSCI 101 - Principles of Programming

14. Exercise • Write a function named change_case() that accepts a sentence and returns the same sentence in all uppercase or all lowercase, without using the methods upper() or lower(). >>> change_case("pApEr","upper") 'PAPER' >>> change_case("PapeR","lower") 'paper' >>> change_case("Can we dO a WHoleSentence","upper") 'CAN WE DO A WHOLE SENTENCE' COMPSCI 101 - Principles of Programming

15. Answer defchange_case(sentence,my_type): uppercase = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"] lowercase = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"] new_sentence = "" for i in range(0,len(sentence)): if ((my_type == "upper" and sentence[i] in lowercase) or (my_type == "lower" and sentence[i] in uppercase)): new_sentence += get_new_letter(sentence[i],my_type) else: new_sentence += sentence[i] return new_sentence COMPSCI 101 - Principles of Programming

16. Helper Functions defget_new_letter(letter, my_type): uppercase = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"] lowercase = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y” ,"z"] if my_type == "upper": for i in range(0,len(lowercase)): if lowercase[i] == letter: return uppercase[i] else: for i in range(0,len(uppercase)): if uppercase[i] == letter: return lowercase[i] COMPSCI 101 - Principles of Programming

17. Summary • Boolean Operators can make code easier to understand • Sequences are easy to manipulate • Both lists and strings are sequences COMPSCI 101 - Principles of Programming

18. Next Tuesday • Slices of Sequences COMPSCI 101 - Principles of Programming