UNIT 5. String Functions and Random Numbers

Transcription

1 UNIT 5 String Functions and Random Numbers

2 DAY 1 String data type String storage in data String indexing

3 I can.. Explain the purpose of the string variable type and how it is stored in memory. Explain indexing of a string (forwards and backwards). Explain and use concatenation and repetition of strings.

4 String Variable Stores text Sequence of characters Assigned using double quotations Ex: str1 = hello str2 = you

5 Type function Determines the type of variable stored in a variable name. Important to know the TYPE of data stored in a variable, as the computer must interact with numeric data different than it interacts with text data type(<variable name>)

6 Let s try it out in Python! Open up the Python IDLE File New File File Save As Name: U5L1StringBasics

7 In Class Project Type the Following (Page 1 of 2) # Simple Conditional If Program # **Insert Today s Date Here** var1 = 4 # creates int variable with value 4 var2 = 5.5 # creates float variable with value 5 var3 = four # creates string variable with value four type1 = type(var1) # saves type of variable 1 type2 = type(var2) # saves type of variable 2 type3 = type(var3) # saves type of variable 3

8 In Class Project Type the Following (Page 2 of 2) print( variable 1 type :, type1) # prints variable type 1 to screen print( variable 2 type :, type2) # prints variable type 2 to screen print( variable 3 type :, type3) # prints variable type 3 to screen

9 Output of Program variable 1 type: <class int > variable 2 type: <class float > variable 3 type: <class string > **Using this method can be helpful when writing a program to check variable types in the program**

10 Numbers vs. Strings Think about what we ve learned so far what operations can we perform with numbers that we can either NOT perform with strings OR work differently with strings.

11 Numbers vs. Strings Throughout this unit we will learn about strings and their functions! Some of the number functions (+, *) can be used on strings but they act in different ways Some functions can ONLY be used with string variables

12 How are Strings Stored in Memory? Character (String) H e l l o Location Name of variable represents a LOCATION in memory Location represents where the string of text begins Each character is stored in order at a specific INDEX The index begins at 0, and increases by 1 for each stored character Spaces, numbers, letters, special characters ALL have an index location in the string

13 Practice Use the string variable below to determine the index of the characters listed in each question. If the character occurs multiple times, list multiple locations Str1 = I love programming & math! 1) Location of: v 4) Location of: p 2) Location of: o 5) Location of: & 3) Location of: m 6) Location of:!

14 Practice Use the string variable below to determine the index location of the characters listed in each question. If the character occurs multiple times, list multiple index locations Str1 = I love programming & math! 1) Location of: v 2) Location of: p 4 7 3) Location of: o 4) Location of: & 3, ) Location of: m 5) Location of:! 13, 14, 21 25

15 Accessing a Specific Location Sometimes you want to access a specific index of a string <string variable name>[<index number>]

16 Practice Use the string below to identify the character represented by each index value below str1 = Help, I m stuck! 1) str1[0] 3) str1[4] 2) str1[8] 5) str[12] 5) str[16]

17 Practice Use the string below to identify the character represented by each index value below str1 = Help, I m stuck! 1) str1[0] 2) str1[4] H, 3) str1[8] 4) str[12] m u 5) str[16] error out of range no character at index 16

18 Index and For Loop Another fantastic way to show indexing is to use a for loop

19 Let s try it out in Python! Open up the Python IDLE File New File File Save As Name: U5L2StringIndex

20 In Class Project Type the Following (Page 1 of 1) # String Index For Loop # **Insert Today s Date Here** message = Hello, Ms. Wardecke! # string declared/initialized for i in message : print(i) # cycle through each character in message # print each character

21 In Class Project Alter the Following (Page 1 of 1) # String Index For Loop # **Insert Today s Date Here** message = Hello, Ms. Wardecke! # string declared/initialized for i in message : # cycle through each character in message print(i,end= ) # print each character # end with space after each **Experiment change the space to something else**

22 Print Statement Additional Option Sometimes instead of a new line you want your print statement to end with a space or character. print(<string to print>, end = <end of print> )

23 Backwards Indexing Prediction: What happens when a negative number is placed in the index?!?!

24 Let s try it out in Python! Open up the Python IDLE File New File File Save As Name: U5L3BackwardsIndex

25 In Class Project Type the Following (Page 1 of 1) # String Index For Loop # **Insert Today s Date Here** message = Hello, Ms. Wardecke! # string declared/initialized for i in range(10) : print( index #-, I, :, end= ) print(message[-i]) # index number # character at index

26 Backwards Indexing Character (String) H e l l o Location Backwards Indexing signals to the computer to count the characters backwards Notice backwards DOES NOT start with 0 Index 0 is always the FIRST character in the string

27 Practice Use the string below to identify the character represented by each index value below str1 = Help, I m stuck! 1) str1[0] 2) str1[-4] 3) str1[-8] 4) str[-12] 5) str[-16]

28 Practice Use the string below to identify the character represented by each index value below str1 = Help, I m stuck! 1) str1[0] 2) str1[-4] H u 3) str1[-8] 4) str[-12] m, 5) str[-16] H

29 Predict: What will the following do?? str1 = My str2 = name str3 = is str4 = Bob str5 =! str6 = str1 + str2 + str3 + str4 + str5 print(str6)

30 Let s try it out in Python! Open up the Python IDLE File New File File Save As Name: U5L4Concatenation

31 In Class Project Type the Following (Page 1 of 1) # Concatenation # **Insert Today s Date Here** str1 = My # declare and initialize string 1 str2 = name # declare and initialize string 2 str3 = is # declare and initialize string 3 str4 = Bob # declare and initialize string 4 str5 =! # declare and initialize string 5 str6 = str1 + str2 + str3 + str4 + str5 # concatenate string 6 print(str6) # print string 6 to the screen

32 Output MynameisBob! What does python do when you place a + between strings??

33 Concatenation The addition of strings When strings are added they are strung together with NO ADDED SPACES BETWEEN This is called concatenation Strings are concatenated (added together) exactly as they are written and combined into one string!

34 Predict: What will the following do?? str1 = My str2 = name str3 = 3*str1 + 2*str2 print(str3)

35 Let s try it out in Python! Open up the Python IDLE File New File File Save As Name: U5L5Repetition

36 In Class Project Type the Following (Page 1 of 1) # Repetition # **Insert Today s Date Here** str1 = hello str2 = world print(3*str1 + 2*str2)

37 Repetition The multiplication of strings When strings are multiplied the computer will output the same string multiple times with no spaces

38 Write the output for the following chunks of code var1 = blue var2 = 11 var3 = purple var4 = 14 1) print(var1, var2) 2) var5 = var1 + var2 print(var5) 3) print(3*var3) 4) print(3*var4) 5) var6 = var1 + + var3 print(var6)

39 Write the output for the following chunks of code var1 = blue var2 = 11 var3 = purple var4 = 10 1) print(var1, var2) blue 11 2) var5 = var1 + var2 blue11 print(var5) 3) print(3*var3) purplepurplepurple 4) print(3*var4) 30 **NOTE: var4 is an INTEGER** 5) var6 = var1 + + var3 blue purple print(var6)

40 Homework Worksheet 5A

41

42 DAY 2 String slicing.

43 I can.. Explain string splicing and how strings can be broken up into parts.

44 Slicing Slicing = purposefully cutting a string based on index location

45 4 Main Types of Slicing 1. <string name>[:]\ 2. <string name>[<number>:<number>] 3. <string name>[<number>:] 4. <string name>[:<number>]

46 Complete Slicing Investigation Complete the Slicing Investigation By the end, you should be able to explain how the segments of code below work in Python Once everyone is done we will regroup, and discuss the findings 1. <string name>[:] 2. <string name>[<number>:<number>] 3. <string name>[<number>:] 4. <string name>[:<number>]

47 <string name>[:] Will print the entire string

48 <string name>[<number>:<number>] Prints a substring of the string The number before the colon represents the STARTING index where the substring should start The number after the colon represents the index AFTER the last character in the substring Ex: str1[ I love computing! str1[2:10] = love com (indices 2-9)

49 <string name>[<number>:] Prints a substring of the string The number before the colon represents the STARTING index where the substring should start Since there is no ending index, the substring will print until the END of the string Ex: str1[ I love computing! str1[2:] = love computing! (indices 2-end)

50 <string name>[:<number>] Prints a substring of the string Since there is no starting index, the substring will start at the beginning of the string The number after the colon represents the index AFTER the last character in the substring Ex: str1[ I love computing! Str1[:10] = I love com (indices start - 9)

51 Practice Use the string below to identify the substring represented by the index slicing below. str1 = Help, I m stuck! 1) str1[:] 4) str1[4:8] 2) str1[3:11] 5) str[:7] 3) str[2:]

52 Practice Use the string below to identify the substring represented by the index slicing below. str1 = Help, I m stuck! 1) str1[:] 2) str1[4:8] Help, I m stuck!, I 3) str1[3:11] 4) str[:7] p, I m s Help, I 5) str[2:] lp, I m stuck!

53 Practice on Your Own: User Name Creation Create a program that meets the following conditions: When a student attends MHS they receive a user name consisting of his or her 4 and 4 4 and 4 : First 4 letters of first name, first four letters of last name Write a program that will prompt the user for his or her first name and for his or her last name. The program will then output the student s username **You may assume every student has a 4 letter first and last name**

54 Homework Worksheet 5B

55

56 DAY 3 ASCII Code and String Length

57 I can.. Explain and use the length, character, and ordinal number functions with strings.

58 ASCII Code Remember = computers ONLY can read machine language which is written in binary (0s and 1s) Bit: a 0 or 1 Byte: eight 0s and 1s in combination Computer CANNOT understand or store characters Each character in a string is represented by a number in binary using the ASCII Code ASCII Code : represent the 128 original characters and take up 1 byte of space in memory Special characters take up 2 bytes in memory

59 ASCII CODE

60 ASCII Code Needed to be consistent between all computer types Think of it as a secret language each character is represented by a number in binary When the computer encounters each letter, it translates the ASCII code value into its appropriate character

61 String comparison Equality Strings compared character by character, starting with the first character Comparing the ASCII code of each character in each string in order Two strings are equal if they are the same length AND if each index s characters are the same This means: Lowercase and uppercase characters of the same letter are DIFFERENT they have different ASCII Code values

62 String Comparison Inequality (<, >, <=, >=) When an inequality is used on strings, the computer compares ASCII Code values Will evaluate to TRUE or FALSE Ex: A < a TRUE Z < a TRUE hello < Hello FALSE 9 < A TRUE

63 ASCII CODES (Generalized) Symbols < Numbers < Upper Case < Lower Case

64 Practice For each statement below decide whether the statement is TRUE or FALSE! 1. Yellow == yellow 2. green <= Green 3. Bears < Packers 4. Packers!= packers 5. It is cold today > It is cool today 6.?What > What? 7. ABCD EFG < ABC DEFG 8. Hello == Hello

65 Practice For each statement below decide whether the statement is TRUE or FALSE! 1. Yellow == yellow FALSE 2. green <= Green FALSE 3. Bears < Packers TRUE 4. Packers!= packers TRUE 5. It is cold today > It is cool today FALSE 6.?What < What? TRUE 7. ABCD EFG < ABC DEFG FALSE 8. Hello == Hello FALSE

66 Let s try it out in Python! Open up the Python IDLE File New File File Save As Name: U5L6AsciiCode

67 In Class Project Type the Following (Page 1 of 2) # ASCII Code # **Insert Today s Date Here** str1 = string #1 # declare and initialize string variable ascii0 = ord(str1[0]) # ASCII code for character at index 1 ascii1 = ord(str1[1]) # ASCII code for character at index 2 ascii2 = ord(str1[2]) # ASCII code for character at index 3

68 In Class Project Type the Following (Page 2 of 2) print( ascii0:, ascii0) print( ascii1:, ascii1) print( ascii2:, ascii2) # print first ASCII code value # print first ASCII code value # print first ASCII code value

69 Ordinal Function - Prediction What information does the ordinal function take in? What does the ordinal function do

70 ord(<single character>) The ordinal function takes in a single character (NOT an entire string) and outputs the ASCII code number (ordinal) associated with the character Examples: ord( a ) = 97 ord( A ) = 65 ord( <single character> ) **can also take in a string index (like example from our previous program)**

71 Character Function - Prediction Using your knowledge of the ordinal function, make a prediction on what the character function will do BEFORE we try it out What information does the character function take in? What does the character function do

72 In Class Project Add the following to the program started in: U5L6AsciiCode # character function experimentation exp1 = chr(77) # finds character with ASCII value 77 exp2 = chr(97) # finds character with ASCII value 97 exp3 = chr(116) # finds character with ASCII value116 exp4 = chr(104) # finds character with ASCII value 104 print(exp1, exp2, exp3, exp4)

73 chr(integer) The character function takes in an integer and outputs the character associated with that ASCII code number Examples: chr(65) = A chr(97) = a chr(integer)

74 Length Function - Prediction Using the name of the function make a prediction about what the length function does in Python What information does the length function take in? What does the length function do?

75 In Class Project Add the following to the program started in: U5L6AsciiCode # length function experimentation message = Hello, there! # creates string variable exp5 = len(message) # finds number of characters in # string called message exp6 = len( Hello! ) # find number of characters in # Hello! print(message, exp5) print( Hello!, exp 6) # prints message and num of chars # prints Hello! and num of chars

76 len( String ) The length function takes in a string and outputs the number of characters in the string Examples: len( HI ) = 2 len( String ) message = Hello, World! len(message) = 13

77 Practice on Your Own: ASCII Code of String Create a program that meets the following conditions: Takes in ANY string from a user. Print the ASCII Code for each character in the string in order. The ASCII codes should appear on one line. Example: Please enter a string: Math ASCII Code:

78 Homework None

79

80 DAY 4 Additional String Functions

81 I can.. Explain and use string functions to manipulate and use the various characteristics of strings.

82 What is we wanted to make yesterday s program in reverse? Let s write a program together that will take in a string of numbers (separated by a comma) and output the string of characters represented by the numbers

83 <string name>.split( <split character ) The dot split function will always be attached to a string, and will split the string at the character each time it appears The string will break up into segments, which will be saved as a list of items to be accessed. <string name>.split( <split character> ) Examples: message = He,llo, Wor,ld

84 Let s try it out in Python! Open up the Python IDLE File New File File Save As Name: U5L7Split

85 In Class Project Type the Following (Page 1 of 1) # Split Function # **Insert Today s Date Here** messagetest = he,llo, wor,ld print(messagetest.split(, )) # string containing commas # splits the string # messagetest every time a # comma is found and prints # each segment (without the # comma) to the screen

86 <string name>.split() SPECIAL NOTE: If no split character is provided and the area inside the parentheses is blank, Python will, by default, split the string at each SPACE

87 Let s reverse yesterday s program using dot split!

88 In Class Project Type the Following (Page 1 of 2) # Split Function # **Insert Today s Date Here** messageascii = input( Please enter in a string of ASCII Code characters separated by a comma: ) # Note: this should all be on one line # input message for user to input ASCII code numbers message = # creates variable to hold string #represented by ASCII code numbers

89 In Class Project Type the Following (Page 2 of 2) # the code below takes the string messageascii and splits it # at every comma. The for loop takes each split chunk, # evaluates the number in the split chunk, turns the number # into its ASCII code character, and concatenates the # character with the message string for num in messageascii.split(, ) codenum = eval(num) message = message + chr(codenum) print(message) # prints the string of characters

90 String Methods Investigation There are many more strings functions to learn! After completing the string investigation you will understand 8 different string methods Once everyone is done, we will regroup and discuss as a class.capitalize().title().lower().replace(, ).count( ).upper().center(#).find( )

91 String Methods (pg. 1) <string name>.capitalize() returns a copy of the string with ONLY the first character capitalized Ex: message = hello Friend message.capitalize() Hello friend <string name>.lower() returns a copy of the string in all lowercase letters Ex: message = hello Friend message.lower() hello friend

92 String Methods (pg. 2) <string name>.upper() returns a copy of the string with all uppercase letters Ex: message = hello Friend message.upper() HELLO FRIEND <string name>.title() returns a copy of the string with the first letter in each word capitalized (title case) Ex: message = hello Friend message.title() Hello friend

93 String Methods (pg. 3) <string name>.count( substring ) counts the number of times a substring (or character) is found in a string and returns the number Ex: message = no I do not like snow message.count( no ) 3 <string name>.find( substring ) returns the FIRST position (index number) of the substring or character this will return a NUMBER Ex: message = I do not like snow message.find( no ) 5

94 String Methods (pg. 4) <string name>.center(integer) if placed inside a print statement, this function will center the string in a given width (integer provided) <string name>.replace( oldsub, newsub ) returns a string with the old substring replaced by the new substring Ex: message = no I do not like snow message.replace( no, yes) yes I do yest like syesw

95 Practice on Your Own: Vowels Program Create a program that meets the following conditions: Takes in ANY string from a user. Calculates the number of vowels in a string, regardless of the case (upper or lower)

96 Homework Worksheet 5C

97

98 DAY 5 Random Numbers

99 I can.. Use random numbers in Python.

100 Random Numbers Numbers that are generated randomly by the computer Used for games and simulations Used for uncertain situations Ex: the chance of flipping a coin heads up is 50% -- but this doesn t mean that every other flip is a head

101 Pseudo Random Numbers How random numbers are generated in Python Works by starting with a seed value This value is fed to the function to produce a random number The current value is then fed back in to produce a new number If you were to start this process over again with the same seed, you d get the same set of random numbers in a row

102 How is the seed determined? Python generates the initial seed value from the day and time when the module is loaded As a result, you get a different seed every time the program is run

103 Must import in random number functions Similar to the turtle graphics, random numbers must be imported into python The following line of code MUST be at the beginning of your program if random numbers are to be used from random import random and/or from random import randrange

104 Main functions for random 1. random() 2. randrange(<integer>, <integer>) 3. randrange(<integer>, <integer>, <integer>)

105 Let s try it out in Python! Open up the Python IDLE File New File File Save As Name: U5L8Random

106 In Class Project Type the Following (Page 1 of 1) # Random Function # **Insert Today s Date Here** from random import random # import random functions for i in range(20): num1 = random() print(num1) # loops 20 times # random number generated # prints rand num to screen

107 random() Generates a random number between 0 and 1 0 is included in the set of numbers 1 is NOT included in the set of numbers Example x = random() 0 <= x < 1

108 In Class Project Add the following to your program(page 1 of 1) # add to type from random import randrange # import randrange print() # insert blank line for i in range(20): num2 = randrange(0,6) print(num2) # loops 20 times # generate rand num # prints rand num to screen

109 randrange(<integer>, <integer>) Generates a random integer number between the two integers The first integer is included in the set of numbers The second integer is NOT included in the set of numbers Examples x = randrange(4, 10) 4, 5, 6, 7, 8, 9 x = randrange(-2, 2) -2, -1, 0, 1

110 In Class Project Add the following to your program(page 1 of 1) # add to type from random import randrange # import randrange print() # insert blank line for i in range(20): # loops 20 times num3 = randrange(0,100, 5) # generate rand num print(num3) # prints rand num to screen

111 randrange(<integer>, <integer>, <integer>) Generates a random integer number between the first two integer, the third integer represents the number of counts between the randomly generated numbers The first integer is included in the set of numbers The second integer is NOT included in the set of numbers The third number represents the number of counts all randomly generated numbers will be apart Examples x = randrange(4, 10, 2) 4, 6, 8 x = randrange(3, 20, 5) 3, 8, 13, 18

112 Practice For each of the following, determine the set of random numbers 1) random() 2) randrange(5, 12) 3) randrange(-3, 0) 4) randrange(40, 100, 20) 5) randrange(5, 20, 4)

113 Practice For each of the following, determine the set of random numbers 1) random() 2) randrange(5, 12) 0 <= x < 1 5, 6, 7, 8, 9, 10, 11 *rand num between 0 and 1, 1 not included* 3) randrange(-3, 0) 4) randrange(10, 10, 90) -3, -2, -1 10, 20, 30, 40, 50, 60, 70, 80 5) randrange(5, 20, 4) 5, 9, 13, 17

114 Math with Random Numbers Let s look into what happens when we perform basic mathematical functions on the random number function Examples: random()*5 randrange(0, 5) + 1

115 Let s try it out in Python! Open up the Python IDLE File New File File Save As Name: U5L8RandomMath

116 In Class Project Type the Following (Page 1 of 1) # Random Math # **Insert Today s Date Here** from random import random from random import randrange # import random functions # import randrange functions for i in range(10): num1 = random()*5 print(num1) # loops 20 times # random number generated # prints rand num to screen

117 Describe in your own words What happened in the previous program when we multiplied the random() function by 5 random()*5

118 Make a prediction What do you think will happen when we multiple randrange() by 5? randrange(1, 6)*5

119 In Class Project Add the Following to your program (Page 1 of 1) print() # print blank line for i in range(10): # loops 20 times num2 = randrange(1, 6)*5 # random number generated print(num2) # prints rand num to screen

120 Multiplication with Random Numbers Generates the random number Then multiples the random number by the value Ex: random()*9 0 <= x < 9 **expands range up to 9** randrange(3, 7)*6 3*6, 4*6, 5*6, 6*6 18, 24, 30, 36

121 Now let s try addition Make predictions what will happen with the following: random() + 7 randrange(2, 7) + 10

122 In Class Project Add the Following to your program (Page 1 of 1) print() # print blank line for i in range(10): num3 = random() + 7 print(num3) print() # loops 20 times # random number generated # prints rand num to screen # print blank line for i in range(10): # loops 20 times num4 = randrange(2, 7) + 10 # rand num generated print(num4) # prints rand num to screen

123 Addition with Random Numbers Generates the random number Adds (or subtracts) the value from the number Ex: 9** random() <= x < 10 **moves range up to starting at randrange(2, 5) , 3+11, , 14, 15

124 Practice For each of the following, determine the set of random numbers 1) random()*6 4) random() ) random()* ) randrange(1, 7)*3 3) randrange(20, 24) + 5 6) randrange(15, 17)*4 + 8

125 Practice For each of the following, determine the set of random numbers 1) random()*6 2) random() <= x < 6 17 <= x < 18 3) random()* ) randrange(1, 7)*3 12 <= x < 15 3, 6, 9, 12, 15, 18 5) randrange(20, 24) + 5 6) randrange(1, 5)* , 26, 27 12, 16, 20, 24

126 Homework Worksheet 5D

127