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Core Elements

Core Elements. Part iii: Iterations. Overview. Tuples Mutable, Immutable object For Loops While Loops. Lists in Python. Lists are mutable objects, e.g. we can modify their contents. Code. >>> my_list = [1, 10, 4, 5 ] # List creation [ ] >>> my_list [2 ] # Accessing the third element

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Core Elements

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  1. Core Elements Part iii: Iterations TPOP

  2. Overview • Tuples • Mutable, Immutable object • For Loops • While Loops TPOP

  3. Lists in Python • Lists are mutable objects, e.g. we can modify their contents. Code >>>my_list = [1, 10, 4, 5] # List creation [ ] >>>my_list[2]# Accessing the third element 4 >>>my_list [1, 10, 4, 5] >>>my_list[2] = 9 # Modifying the third element >>>my_list# The modified list [1, 10, 9, 5] >>> TPOP

  4. Tuples in Python • Tuples are immutable objects, e.g. we CANNOT modify their contents. Code >>>my_tuple= (1, 10, 4, 5)# tuple creation ( ,) >>>my_tuple[2]# Accessing the third element 4 >>>my_tuple (1, 10, 4, 5) >>>my_tuple[2] = 9 # Modifying the third element Traceback (most recent call last): File "<pyshell#15>", line 1, in <module> my_tuple[2] = 9 TypeError: 'tuple' object does not support item assignment >>> TPOP

  5. Tuples in Python • Tuples are immutable objects, e.g. we CANNOT modify their contents. • Note that numbers and strings are immutable too. Code >>>my_t= (1, 10, 4, 5)# tuple creation ( ,) >>>my_t = my_t(:2) + (9,) + my_t(3:) # Modifying the third element >>>my_t (1, 10, 9, 5) TPOP

  6. Be Careful • Example: Code >>>lst1 = lst2 = [2,4,6,8] >>> t1 = t2 = (1,3,7,9) >>>lst1 [2, 4, 6, 8] >>>lst2 [2, 4, 6, 8] >>> t1 (1, 3, 7, 9) >>> t2 (1, 3, 7, 9) >>> TPOP

  7. Be Careful • Example: A change in t2 does not affect t1 Code >>>t2 = t2[:2] + (5, ) + t2[3:] # Modifying the third element t2 >>> lst2[2] = 5 # Modifying the third element of lst2 >>>t1 (1, 3, 7, 9) >>> t2 (1, 3, 5, 9) >>> TPOP

  8. Be Careful • Example: A change in t2 does not affect t1 Code >>>t2 = t2[:2] + (5, ) + t2[3:] # Modifying the third element t2 >>> lst2[2] = 5 # Modifying the third element of lst2 >>>t1 (1, 3, 7, 9) >>> t2 (1, 3, 5, 9) >>> lst1 [2, 4, 5, 8] >>> lst2 [2, 4, 5, 8] >>> A change in lst2 does affect lst1 TPOP

  9. Be Careful • State Diagram: 6 4 2 8 0 1 2 3 lst1 Code lst2 >>>lst1 = lst2 = [2,4,6,8] >>> TPOP

  10. Be Careful • State Diagram: 7 6 4 3 2 1 8 9 0 1 2 3 0 1 2 3 lst1 Code lst2 >>>lst1 = lst2 = [2,4,6,8] >>> t1 = t2 = (1,3,7,9) >>> t1 t2 TPOP

  11. Be Careful • State Diagram: 6 7 5 3 4 3 1 2 1 9 9 8 0 1 2 3 0 1 2 3 0 1 2 3 lst1 Code lst2 >>>lst1 = lst2 = [2,4,6,8] >>> t1 = t2 = (1,3,7,9) >>>t2 = t2[:2] + (5, ) + t2[3:] >>> t1 t2 TPOP

  12. Be Careful • State Diagram: 5 6 7 3 3 4 1 1 2 8 9 9 0 1 2 3 0 1 2 3 0 1 2 3 5 lst1 Code lst2 >>>lst1 = lst2 = [2,4,6,8] >>> t1 = t2 = (1,3,7,9) >>>t2 = t2[:2] + (5, ) + t2[3:] >>>lst2[2] = 5 >>> t1 t2 TPOP

  13. Be Careful • State Diagram: 5 5 7 5 4 3 3 4 2 1 1 2 9 8 9 8 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 lst1 Code lst2 >>>lst1 = lst2 = [2,4,6,8] >>> t1 = t2 = (1,3,7,9) >>>t2 = t2[:2] + (5, ) + t2[3:] >>>lst2[2] = 5 >>> >>>lst2 = [2, 4, 5, 8] >>> t1 t2 TPOP

  14. Be Careful • State Diagram: 7 5 5 5 4 3 4 3 1 2 2 1 8 9 9 8 0 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 lst1 Code lst2 >>>lst1 = lst2 = [2,4,6,8] >>> t1 = t2 = (1,3,7,9) >>>t2 = t2[:2] + (5, ) + t2[3:] >>>lst2[2] = 5 >>> >>>lst2 = [2, 4, 5, 8] >>> lst2[2] = 0 t1 t2 TPOP

  15. Swapping Values • State Diagram: 5 num_one 9 Code num_two >>>num_one = 5 >>>num_two = 9 >>> TPOP

  16. Swapping Values • State Diagram: First Attempt 5 num_one 9 Code num_two >>>num_one = 5 >>>num_two = 9 >>>num_one = num_two >>>num_two = num_one >>> TPOP

  17. Swapping Values • State Diagram: Second Attempt 5 num_one 9 Code num_two >>>num_one = 5 >>>num_two = 9 >>>temp = num_two >>>num_two = num_one >>> num_one = temp >>> temp TPOP

  18. Iteration Definite & indefinite loops TPOP

  19. Iteration • We need a structure to execute a sequence of statements multiple times in succession • So Far, we have to write the sequence of statement n times to achieve n repetition • How can we proceed if we are not sure how many times it needs to be repeated? TPOP

  20. Definite Loop: For statement • The simplest kind of loop • It will execute a definite amount of times • The for loop statement for <var> in <iterable>: <body> • Iterable can return its element one at a time • The body of the loop can be any sequence of Python statements • The variable after the keyword for is called the loop index. TPOP

  21. Example Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print"--> inside loop: square of", str(val), "is", str(square_val) print"After the for loop" Before the for loop --> inside loop: square of 1 is 1 --> inside loop: square of 2 is 4 --> inside loop: square of 3 is 9 After the for loop TPOP

  22. Example Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" TPOP

  23. Example val 3 2 1 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop TPOP

  24. Example val square_val 3 2 1 1 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop TPOP

  25. Example val square_val 3 2 1 1 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop --> inside loop: square of 1 is 1 TPOP

  26. Example val square_val 3 2 1 1 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop --> inside loop: square of 1 is 1 TPOP

  27. Example val square_val 3 2 4 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop --> inside loop: square of 1 is 1 TPOP

  28. Example val square_val 3 2 4 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop --> inside loop: square of 1 is 1 --> inside loop: square of 2 is 4 TPOP

  29. Example val square_val 3 2 4 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop --> inside loop: square of 1 is 1 --> inside loop: square of 2 is 4 TPOP

  30. Example val square_val 3 9 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop --> inside loop: square of 1 is 1 --> inside loop: square of 2 is 4 TPOP

  31. Example val square_val 3 9 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop --> inside loop: square of 1 is 1 --> inside loop: square of 2 is 4 --> inside loop: square of 3 is 9 TPOP

  32. Example val square_val 3 9 Code Python shell print"Before the for loop" forvalin [1,2,3]: square_val = val * val print . . . print "After the for loop" Before the for loop --> inside loop: square of 1 is 1 --> inside loop: square of 2 is 4 --> inside loop: square of 3 is 9 After the for loop TPOP

  33. Indefinite Loop: While Statement • An indefinite loop keeps iterating until certain condition are met (conditional loop) • There is no guarantee ahead of time regarding how many times the loop will go around • zero time • x-times • indefinitely TPOP

  34. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  35. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  36. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  37. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  38. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  39. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  40. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  41. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  42. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  43. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  44. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  45. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  46. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  47. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  48. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> False <condition> True <body> TPOP

  49. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> • The <body> usually contains statements that modify the evaluation of <condition> at some point False <condition> True <body> TPOP

  50. Indefinite Loop: While Statement • The while loop statement while <condition>: <body> • The <body> usually contains statements that modify the evaluation of <condition> at some point • The <body> may never be executed! False <condition> True <body> TPOP

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