CSCI 141 Computer Programming I. Filip Jagodzinski

Transcription

1 Filip Jagodzinski

2 Announcement Using online resources for help I want you to learn from others I want you to learn how to use (good) online resources Learning on your own is a good thing

3 Announcement Using online resources for help I want you to learn from others I want you to learn how to use (good) online resources Learning on your own is a good thing Two scenarios : You learn about the break or continue keywords, by reading a post on [insert your favorite website here] You learn about sys.exit(0) or os._exit(0), by reading a post on [insert your favorite website here]

4 Announcement Using online resources for help I want you to learn from others I want you to learn how to use (good) online resources Learning on your own is a good thing Two scenarios : You learn about the break or continue keywords, by reading a post on [insert your favorite website here] You learn about sys.exit(0) or os._exit(0), by reading a post on [insert your favorite website here] Which of the two scenarios is allowed? And how can you determine if you ve learned about these python features (in which case you can use them), or if you ve simply cut-and-paste (which is plagiarism)?

5 From Last Time Motivation : Computers (via computer programs) are reaaaaaly good at monotonous tasks. Humans no so much

6 From Last Time Motivation : Computers (via computer programs) are reaaaaaly good at monotonous tasks. Humans no so much For a bank Account balance of , and assuming that each year the account earns 10% interest that is added to the account s value, what is the account s value after 5 years? One by-hand approach is the following:

7 From Last Time Motivation : Computers (via computer programs) are reaaaaaly good at monotonous tasks. Humans no so much For a bank Account balance of , and assuming that each year the account earns 10% interest that is added to the account s value, what is the account s value after 5 years? One by-hand approach is the following: But if we want to compute the account s value after 500 years.

8 From Last Time Task : Be able to explain in your own words what the above piece of code accomplishes

9 From Last Time Task : Be able to explain in your own words what the above piece of code accomplishes The keyword for specifies functionality in python for repeatedly performing a task. The iterator variable x takes on values output by the range function. For EACH value of x, the code block (or body) of the for loop is executed. x=0 x=1 x=2

10 From Last Time Motivation : Computers (via computer programs) are reaaaaaly good at monotonous tasks. Humans no so much For a bank Account balance of , and assuming that each year the account earns 10% interest that is added to the account s value, what is the account s value after 500 years?

11 From Last Time Motivation : Computers (via computer programs) are reaaaaaly good at monotonous tasks. Humans no so much For a bank Account balance of , and assuming that each year the account earns 10% interest that is added to the account s value, what is the account s value after 500 years? Q: Where is the code block for the for loop?

12 From Last Time Motivation : Computers (via computer programs) are reaaaaaly good at monotonous tasks. Humans no so much For a bank Account balance of , and assuming that each year the account earns 10% interest that is added to the account s value, what is the account s value after 500 years? Q: How many times will the balance be printed?

13 From Last Time Motivation : Computers (via computer programs) are reaaaaaly good at monotonous tasks. Humans no so much For a bank Account balance of , and assuming that each year the account earns 10% interest that is added to the account s value, what is the account s value after 500 years? Q: Why are we using the range 0 through 500?

14 From Last Time Motivation : Computers (via computer programs) are reaaaaaly good at monotonous tasks. Humans no so much For a bank Account balance of , and assuming that each year the account earns 10% interest that is added to the account s value, what is the account s value after 500 years? Q: Could we have used range(1,501)?

15 Today s quiz Please do not us a calculator, computer, smart phone, etc. (The quizzes are not an exercise in how well you can type code into Thonny)

16 Today Incrementing in for loops Accumulators A more detailed example import

17 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1

18 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Would this work? Why or why not?

19 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Would this work? Why or why not? No. This prints out ALL numbers from 0 through 99. However you ve learned of an operator that you can use in combination with the equality operator to see if a number divisible by another number gives a zero remainder

20 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 This is one of many possible solutions Step-by-step walk through

21 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99

22 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Notice the indentation : This is the code block (or body) of the for loop Q: When is it executed?

23 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Notice the indentation : This is the code block for the if statement. Q: When is this code block executed?

24 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 x is the loop (or iterator) variable, so for each value of x, the code block (or body) of the for loop will be executed

25 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Q: What is 0 modulus 2? This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 When x=0, the code block will be executed. What does the code block do? It checks if 0 modulus 2 is equal to 0. If it is, then the value of x is printed

26 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Q: What is 0 modulus 2? This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, When x=0, the code block will be executed. What does the code block do? It checks if 0 modulus 2 is equal to 0. If it is, then the value of x is printed

27 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Q: What is 0 modulus 2? This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 When x=0, the code block will be executed. What does the code block do? It checks if 0 modulus 2 is equal to 0. If it is, then the value of x is printed

28 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Q: What is 0 modulus 2? 0 r This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 When x=0, the code block will be executed. What does the code block do? It checks if 0 modulus 2 is equal to 0. If it is, then the value of x is printed

29 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Output 0 This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 When x=0, the code block will be executed. What does the code block do? It checks if 0 modulus 2 is equal to 0. If it is, then the value of x is printed

30 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Output 0 This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 When x=1, the code block will be executed. What does the code block do? It checks if 1 modulus 2 is equal to 0. If it is, then the value of x is printed

31 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Output 0 2 This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 When x=2, the code block will be executed. What does the code block do? It checks if 2 modulus 2 is equal to 0. If it is, then the value of x is printed

32 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Output 0 2 This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 When x=3, the code block will be executed. What does the code block do? It checks if 3 modulus 2 is equal to 0. If it is, then the value of x is printed

33 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Output This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 When x=4, the code block will be executed. What does the code block do? It checks if 4 modulus 2 is equal to 0. If it is, then the value of x is printed

34 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Output This will generate a list of numbers from 0 up to but not including 100 0, 1, 2, 3, 4,, 99 When x=99, the code block will be executed. What does the code block do? It checks if 99 modulus 2 is equal to 0. If it is, then the value of x is printed

35 The most recent take-home exercise Write a program that On-the-fly coding/demonstration Prompts the user for an upper limit. Assume the user will always input (via the keyboard) an integer. Prompts the user for a lower limit. Assume the user will always input (via the keyboard) an integer that is less than the upper limit. Prints to the screen all multiples of the lower limit number in the range from the lower limit to the upper limit (inclusive) Two invocations of such a program are shown below

36 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Output Q: Is there another way to accomplish this same task? Q: Can this be done with 2 lines of code?

37 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Q: Is there another way to accomplish this same task? The range function can have a third argument, that specifies the increment value of each successive number

38 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Q: Is there another way to accomplish this same task? The range function can have a third argument, that specifies the increment value of each successive number This specifies generate numbers from 0 up to but not including 100, in increments of 2

39 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Q: Do these pieces of code output the same thing?

40 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Q: Do these pieces of code output the same thing? They do. Q: Is one better than the other?

41 Other forms of for-loops Task : Print only the even integers greater than -1 but less than 100. How could you do this using Python and what you ve learned already? In class exercise 1 Q: Do these pieces of code output the same thing? They do. Q: Is one better than the other? Not necessarily

42 For loops another tricky example Q: What does the following code output? A. B. C. D. The value of avalue is 4 The value of avalue is 6 The value of avalue is 6 The value of avalue is 4 nothing An error message because the code has an error

43 For loops another tricky example Q: What does the following code output? A. B. C. D. The value of avalue is 4 The value of avalue is 6 The value of avalue is 6 The value of avalue is 4 nothing An error message because the code has an error As a first step, what list of numbers does range(4, 6, -2) generate?

44 For loops another tricky example Q: What does the following code output? A. B. C. D. The value of avalue is 4 The value of avalue is 6 The value of avalue is 6 The value of avalue is 4 nothing An error message because the code has an error As a first step, what list of numbers does range(4, 6, -2) generate? An empty list. Starting at 4, proceeding in increments of -2 until it reaching 6 there is no such list.

45 For loops another tricky example Q: What does the following code output? A. B. C. D. The value of avalue is 4 The value of avalue is 6 The value of avalue is 6 The value of avalue is 4 nothing An error message because the code has an error 4,6,-2 range { }

46 For loops another tricky example Q: What does the following code output? A. B. C. D. The value of avalue is 4 The value of avalue is 6 The value of avalue is 6 The value of avalue is 4 nothing An error message because the code has an error 4,6,-2 range { } anum assumes, in turn, each of the values in the list generated by range, but range returns a list with no elements, therefore how many times does the code block for the for loop execute?

47 For loops another tricky example Q: What does the following code output? never executed A. B. C. D. The value of avalue is 4 The value of avalue is 6 The value of avalue is 6 The value of avalue is 4 nothing An error message because the code has an error 4,6,-2 range { } Zero times. Therefore, the variable avalue is never declared nor assigned a value, so when the print statement attempts to use the value for the variable avalue

48 For loops another tricky example Q: What does the following code output? never executed A. B. C. D. The value of avalue is 4 The value of avalue is 6 The value of avalue is 6 The value of avalue is 4 nothing An error message because the code has an error There is another reason called scope why this code produces an error. We ll talk about variable scope when we start writing our own functions.

49 For loops another tricky example Q: What does the following code output? never executed A. B. C. D. The value of avalue is 4 The value of avalue is 6 The value of avalue is 6 The value of avalue is 4 nothing An error message because the code has an error An error occurs. Specifically, a Name Error, which occurs when you try to use a variable before it has been assigned a value

50 Accumulators Remember that the code block (or body) of a for loop can contain multiple lines of code. Q: What does this code accomplish

51 Accumulators Remember that the code block (or body) of a for loop can contain multiple lines of code. Identify the code block Q: How many iterations are performed? Q: What is the output?

52 Accumulators Remember that the code block (or body) of a for loop can contain multiple lines of code. These are often referred to as accumulators because they are updated (or accumulate values) in the body of the for loop.

53 Accumulators Q: What is the output of the following code? In-class exercise 2 On-the board explanation of how this code is executed

54 Import There is functionality available for your use which is part of the core of python. Lab 4 teaches you how to generate random numbers, and that capability is in the random module. To use the capability in a module, you must explicitly import it

55 Import There is functionality available for your use which is part of the core of python. Lab 4 teaches you how to generate random numbers, and that capability is in the random module. To use the capability in a module, you must explicitly import it Q: What functionality and/or capabilities are available for your use in the random module?

56 Import There is functionality available for your use which is part of the core of python. Lab 4 teaches you how to generate random numbers, and that capability is in the random module. To use the capability in a module, you must explicitly import it Q: What functionality and/or capabilities are available for your use in the random module? Just as existing functions in python contain code that somebody has written and you should think of as a black box, the random module, too, has code that somebody has written and which is now part of python. You can see the code if you d like (demo)

57 Import There is functionality available for your use which is part of the core of python. Lab 4 teaches you how to generate random numbers, and that capability is in the random module. To use the capability in a module, you must explicitly import it Q: What functionality and/or capabilities are available for your use in the random module? Don t worry about the code that is inside the random module. Just as You existing don t functions need to memorize in python it contain If you code read that somebody it you won t has understand much of what is there written You ll and you learn should about think classes, of a the self keyword, class black box, variables, the random overriding, module, inheritance, too, overloading, class has code functions, that somebody etc. in later has CS written courses and which is now part of python. For You the can time see being the code just be if you d thankful like that somebody has written these modules, which allows you to write fairly complicated programs

58 Import Task : Write a program that prints 11 random numbers Q: How do you start

59 Import Task : Write a program that prints 11 random numbers Q: How do you start Looking at the API, there are many functions available for your use when you import the random module. They include : random() getrandbits(k) sample(population, k) randint(a,b) randrange(start, stop, step) randrange(start, stop)

60 Import Task : Write a program that prints 11 random numbers Q: How do you start Looking at the API, there are many functions available for your use when you import the random module. They include : random() Assume you select this one getrandbits(k) sample(population, k) randint(a,b) randrange(start, stop, step) randrange(start, stop) You ll gain experience with many of these. Which one you select to use is dependent on the problem that you want to solve.

61 Import Task : Write a program that prints 11 random numbers random() avar = random() print(avar) Q: Does this work? Why or why not?

62 Import Task : Write a program that prints 11 random numbers random() avar = random() print(avar) Q: Does this work? Why or why not? This generates an error because in order to use the functions in a module (that is not part of the core of python) you must first import that module Q: What is the fix?

63 Import Task : Write a program that prints 11 random numbers random() import random print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) Q: What does this code output? In order to invoke a function that is available in a module, first write the name of the module, followed by dot, followed by the name of the function.

64 Import Task : Write a program that prints 11 random numbers random() import random print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) print(random.random()) Q: What does this code output? This is OKAY, but what if you want integers!

65 Import Task : Write a program that prints 11 random numbers integers In class exercise 3 (take home) random() getrandbits(k) sample(population, k) randint(a,b) randrange(start, stop, step) randrange(start, stop) Back to the API Write two programs, which use DIFFERENT functions from random, and which print to the screen 11 random integers

66 Take home exercise Write python code that will print the first 10 positive multiples of the number 34 whose ones digit is NOT 0 nor 5. Hint : the digits are 34, 68, 102, 136, 204, 238, 272, 306, 374, 408

67 Up next Lists Functions