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Lecture 20 – Boolean Operators Dr. Patricia J. Riddle.

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1 Lecture 20 – Boolean Operators Dr. Patricia J. Riddle

2  At the end of this lecture, students should be able to:  Use and, or and not in conditional conditions  Understand basic truth tables  Use short circuit evaluation 2COMPSCI Principles of Programming

3  Booleans represent truth values  True  False  Relational operators compare two different things  Evaluate to Boolean values  ==  <  <=  >  >=  != 3COMPSCI Principles of Programming

4  Boolean Operators are and, or and not: if palindrome("word") if not palindrome("word") if palindrome("word") and heterogram("word") if palindrome("word") or heterogram("word") 4COMPSCI Principles of Programming

5 PQnot PP and QP or Q True FalseTrue False True FalseTrue FalseTrue False TrueFalse 5COMPSCI Principles of Programming

6  Write a function named is_a_leap_year() that accepts a year as a parameter and returns True if the year is a leap year and False otherwise.  A year is a leap year if it is divisible by 400, or divisible by 4 but not by COMPSCI Principles of Programming

7  From lecture 12, slide 19 def is_leap_year(year): if year % 400 == 0: return True elif year % 100 == 0: return False elif year % 4 == 0: return True else: return False 7COMPSCI Principles of Programming

8 def is_a_leap_year(year): if not isinstance(year,int): print("year is not an integer") return False if (year % 400) == 0 or ((year % 4) == 0 and (year % 100) != 0): return True return False 8COMPSCI Principles of Programming

9  If A and B  B is not evaluated unless A is True  If A or B  B is not evaluated unless A is False  Examples If divisor != 0 and numerator/divisor > 4: If divisor = 0 or numerator/divisor > 4: 9COMPSCI Principles of Programming

10  Write a function named find_names_with() that accepts a letter, a location and a list of names, and returns the list of names that have the letter in the specified location. find_names_with("r", 3, ["Sara","Fred","Al","Tar"]) ['Sara', 'Tar'] 10COMPSCI Principles of Programming

11 def find_names_with(letter, place, names_list): name_list = [] for name in names_list: if len(name) >= place and name[place-1] == letter: name_list += [name] return name_list 11COMPSCI Principles of Programming

12  Write a function named pangram() that accepts a string parameter and returns True if the string is a pangram and False otherwise.  A pangram is a sentence which contains every letter in the alphabet. “The quick brown fox jumps over the lazy dog” Perfect panagrams “TV quiz jock, Mr. PhD, bags few lynx” “Glum Schwartzkopf vex'd by NJ IQ” “Blowzy night-frumps vex'd Jack Q” 12COMPSCI Principles of Programming

13 def pangram(sentence): if not isinstance(sentence,str): print("sentence is not a string") return False alphabet = ["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"] for letter in alphabet: if letter not in sentence: return False return True 13COMPSCI Principles of Programming

14  Write a function named pangram2() that accepts a string parameter and returns True if it is a Pangram and False otherwise, and works for both uppercase and lowercase letters Perfect panagrams “TV quiz jock, Mr. PhD, bags few lynx” “Glum Schwartzkopf vex'd by NJ IQ” “Blowzy night-frumps vex'd Jack Q” 14COMPSCI Principles of Programming

15 def pangram2(sentence): if not isinstance(sentence,str): print("sentence is not a string") return False alphabet = ["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"] capital_alphabet = ["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"] alphabet_range = range(0,len(alphabet)) for index in alphabet_range: if alphabet[index] not in sentence and capital_alphabet[index] not in sentence: return False return True 15COMPSCI Principles of Programming

16 The universe of the Game of Life is an infinite two-dimensional orthogonal grid of square cells, each of which is in one of two possible states, alive or dead. Every cell interacts with its 8 neighbours, which are the cells that are horizontally, vertically, or diagonally adjacent. At each step in time, the following transitions occur:  Any live cell with fewer than two live neighbours dies, as if caused by under-population.  Any live cell with two or three live neighbours lives on to the next generation.  Any live cell with more than three live neighbours dies, as if by overcrowding.  Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.  Wikipedia 16COMPSCI Principles of Programming

17  Write a function named is_alive() that accepts 2 parameters: a Boolean value (alive) and a number between 1 and 8 (live_neighbours) and returns True if the cell should turn on and False otherwise >>> is_alive(True,1) False >>> is_alive(True,3) True >>> is_alive(False,3) True >>> is_alive(False,4) False 17COMPSCI Principles of Programming

18  Nested if statements can be hard to read def is_alive(alive,neighbours_alive): if alive: if neighbours_alive < 2: return False if neighbours_alive > 3: return False return True if neighbours_alive == 3: return True return False 18COMPSCI Principles of Programming

19 def is_alive2(alive,neighbours_alive): its_dead = False its_alive = True if alive and (neighbours_alive 3): return its_dead if not alive and neighbours_alive != 3: return its_dead return its_alive 19COMPSCI Principles of Programming

20  Basic Truth tables  and  or  not  Use of Complex conditions:  Use of “and”, “not”, and “or”  Benefits of Short Circuit evaluation:  Allows you to write code that will not trigger error messages 20COMPSCI Principles of Programming

21  Complex String Processing 21COMPSCI Principles of Programming


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