Course A201: Introduction to Programming

1. Course A201:Introduction to Programming 09/30/2010

2. Outlines for this week • How to write for loops • Function range() • Python membership operator: in • Write nested for loops to print out certain shapes • More on Strings • String Indexing • Function len() • String functions • Finish Part-1, understand what to do in Part-2

3. for loops vs while loops number = 1 While number< 11: print(number) count += 1 number_list = range(1, 11, 1) for number innumber_list: print(number) • The output will be exactly the same

4. Function range() [functions] • input1, input2, input3, … • You give me some inputs I am a function. I will perform a certain job. • I give you some outputs back, explicitly or implicitly • output1, output2, output3, …

5. Function range() • Example of how to use range(): >>> range() ERROR! range expected at least 1 arguments >>> range(10) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> ans = range(10) >>> ans [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] • 10 is not included!

6. Function range() • So, we know that range() will require at least one argument, let’s see how it works when there’re two: >>> range(3, 11) [3, 4, 5, 6, 7, 8, 9,10] >>> range(-10,1) [-10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0] >>> range(10,1) [] • Empty! when second argument is smaller than the first one, and there is no third argument.

7. Function range() • Three arguments? >>> range(3, 11, 2) [3, 5, 7, 9] >>> range(10, 1, -1) [10, 9, 8, 7, 6, 5, 4, 3, 2] >>> range(-10, -1, -1) [] >>> range(2, 8, 0) ERROR! range() step argument must not be zero • The 3rd argument is the ‘step argument’. The default value is 1. • Empty!

8. For loops name = “Linger Xu” foraain name: print(aa) number_list = range(-10, 1) for number innumber_list: print(number)

9. Python membership operator: in • The variable name is a string, “Linger Xu” [foraain name] fetch every letter in this string sequentially, and put it into aa • The variable number_list contains a list of numbers: [for number innumber_list ] fetch every number in this list sequentially, and put it into number • Go throught every member of a specified sequence: • -10, -9, -8, …

10. Python membership operator: in • user = “5198” if “1” in user: print(“Number 1 is in”, user) if “0” not in user: print(“Number 0 is not in”, user) • membership operator: in / not in

11. Python membership operator: in • The variable after in must be holding a sequence of values, such as string and list. number_list = 9 for number innumber_list: print(number) ERROR! 'int' object is not iterable

12. For loops • Finish first problem in Part1 , Assignment 4 Write a program that counts for the user using a for loop as shown in class. Let the user enter the starting number, the ending number, and the amount by which to count.

13. Write nested for loops • How to print out: 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7

14. Write nested for loops row_size = 5 column_size = 7 for row in range(row_size): for column in range(column_size ): print(column+1, end=“ ”) print() • Loop within a loop. Look out for indentation!!

15. Write nested for loops • What will happen if you indent the second print also? row_size = 5 column_size = 7 for row in range(row_size): for column in range(column_size ): print(column+1, end=“ ”) print()

16. Write nested for loops • How to print out: 1 1 1 1 1 1 1 2 2 2 2 2 2 2 3 3 3 3 3 3 3 4 4 4 4 4 4 4 5 5 5 5 5 5 5

17. Write nested for loops row_size = 5 column_size = 7 for row in range(row_size): for column in range(column_size ): print(row+1, end=“ ”) print() • Just change column in 5th line to row

18. Write nested for loops • Finish second problem in Part1 , Assignment 4 Scalable Patterns: What do the following codes print? • Understand the 1st problem in Part2

19. String: Indexing • str=“killer rabbit” • Ex: str[0] returns “k” str[1] returns “i” str[3] returns “l” str[-3] returns “b” str[-14] returns Error! Index out of range!

20. String: Indexing • Try this program (in textbook Chapter 4): import random word = "index" print("The word is: ", word, "\n“) high = len(word) low = -len(word) for i in range(10): position = random.randrange(low, high) print("word[", position, "]\t", word[position])

21. String: Indexing • Count the occurrence of one letter in a string str1=“killer rabbit” target =“i” count = 0 for letter in str1: if letter == target: count += 1 print(“There’re ” + str(count) + “ ‘i‘s in string: ” + str(str1) )

22. Function len() • Return an integer that represents how many elements are there in this specified sequence >>> user = input(“Type a word: “) >>> user = “I like Python.” >>> len(user) 14 >>> user = “5198” >>> len(user) 4

23. String: methods quote = "I like Python.“ • quote.upper() -> capitalize everything –“I LIKE PYTHON.” • quote.lower() -> small letter everything –“I like python.” • quote.title() -> capitalize the first letter of every word –“I Like Python.”

24. String: methods quote = "I like Python.“ • quote.strip() -> removes spaces, tabs, newlines before and after • quote.replace(“like”, “dislike programming in”) –“I dislike programming in Python.” • Try quote.center(50)

25. String methods vs Built-in functions • When you want to use a string method, you’ve got to use the dot“.”: >>> quote = "I like Python." >>> quote.upper() 'I LIKE PYTHON.' >>> upper(quote) <- Error! • While built-in function >>> len(quote) >>> range(10)

26. String: Indexing and slicing • Understand the 2nd and 3rd problem in Part2

27. Have a nice evening! • See you tomorrow~