LEARNING TO PROGRAM WITH PYTHON

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LEARNING TO PROGRAM WITH PYTHON

Richard L. Halterman

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https://www.cs.uky.edu/~keen/115/Haltermanpythonbook.pdf

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关键词：Learning Program earning python Learn

1. Listing 10.1: sortintegers.py
   
2. 1 from random import randrange
   
3. 2
   
4. 3 def random_list():
   
5. 4 '''
   
6. 5 Produce a list of pseudorandom integers.
   
7. 6 The list's length is chosen pseudorandomly in the
   
8. 7 range 3-20.
   
9. 8 The integers in the list range from -50 to 50.
   
10. 9 '''
    
11. 10 result = []
    
12. 11 count = randrange(3, 20)
    
13. 12 for i in range(count):
    
14. 13 result += [randrange(-50, 50)]
    
15. 14 return result
    
16. 15
    
17. 16 def selection_sort(lst):
    
18. 17 '''
    
19. 18 Arranges the elements of list lst in ascending order.
    
20. The contents of lst are physically rearranged.
    
21. 20 '''
    
22. 21 n = len(lst)
    
23. 22 for i in range(n - 1):
    
24. 23 # Note: i, small, and j represent positions within lst
    
25. 24 # lst[i], lst[small], and lst[j] represent the elements at
    
26. 25 # those positions.
    
27. 26 # small is the position of the smallest value we've seen
    
28. 27 # so far; we use it to find the smallest value less
    
29. 28 # than lst[i]
    
30. 29 small = i
    
31. 30 # See if a smaller value can be found later in the list
    
32. 31 # Consider all the elements at position j, where i < j < n
    
33. 32 for j in range(i + 1, n):
    
34. 33 if lst[j] < lst[small]:
    
35. 34 small = j # Found a smaller value
    
36. 35 # Swap lst[i] and lst[small], if a smaller value was found
    
37. 36 if i != small:
    
38. 37 lst[i], lst[small] = lst[small], lst[i]
    
39. 38
    
40. 39 def main():
    
41. 40 '''
    
42. 41 Tests the selection_sort function
    
43. 42 '''
    
44. 43 for n in range(10):
    
45. 44 col = random_list()
    
46. 45 print(col)
    
47. 46 selection_sort(col)
    
48. 47 print(col)
    
49. 48 print('==============================')
    
50. 49
    
51. 50 main()

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1. Listing 10.2: flexiblesort.py
   
2. 1 def random_list():
   
3. 2 '''
   
4. 3 Produce a list of pseudorandom integers.
   
5. 4 The list's length is chosen pseudorandomly in the
   
6. 5 range 3-20.
   
7. 6 The integers in the list range from -50 to 50.
   
8. 7 '''
   
9. 8 from random import randrange
   
10. 9 result = []
    
11. 10 count = randrange(3, 20)
    
12. 11 for i in range(count):
    
13. 12 result += [randrange(-50, 50)]
    
14. 13 return result
    
15. 14
    
16. 15
    
17. 16 def less_than(m, n):
    
18. 17 return m < n
    
19. 18
    
20. 19 def greater_than(m, n):
    
21. 20 return m > n
    
22. 21
    
23. 22
    
24. 23 def selection_sort(lst, cmp):
    
25. 24 '''
    
26. 25 Arranges the elements of list lst in ascending order.
    
27. 26 The comparer function cmp is used to order the elements.
    
28. 27 The contents of lst are physically rearranged.
    
29. 28 '''
    
30. 29 n = len(lst)
    
31. 30 for i in range(n - 1):
    
32. 31 # Note: i, small, and j represent positions within lst
    
33. 32 # lst[i], lst[small], and lst[j] represent the elements at
    
34. 33 # those positions.
    
35. 34 # small is the position of the smallest value we've seen
    
36. 35 # so far; we use it to find the smallest value less
    
37. 36 # than lst[i]
    
38. 
    
39. small = i
    
40. 38 # See if a smaller value can be found later in the list
    
41. 39 # Consider all the elements at position j, where i < j < n.
    
42. 40 for j in range(i + 1, n):
    
43. 41 if cmp(lst[j], lst[small]):
    
44. 42 small = j # Found a smaller value
    
45. 43 # Swap lst[i] and lst[small], if a smaller value was found
    
46. 44 if i != small:
    
47. 45 lst[i], lst[small] = lst[small], lst[i]
    
48. 46
    
49. 47 def main():
    
50. 48 '''
    
51. 49 Tests the selection_sort function
    
52. 50 '''
    
53. 51 original = random_list() # Make a random list
    
54. 52 working = original[:] # Make a working copy of the list
    
55. 53 print('Original: ', working)
    
56. 54 selection_sort(working, less_than) # Sort ascending
    
57. 55 print('Ascending: ', working)
    
58. 56 working = original[:] # Make a working copy of the list
    
59. 57 print('Original: ', working)
    
60. 58 selection_sort(working, greater_than) # Sort descending
    
61. 59 print('Descending:', working)
    
62. 60
    
63. 61 main()

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1. Listing 10.3: linearsearch.py
   
2. 1 def locate(lst, seek):
   
3. 2 '''
   
4. 3 Returns the index of element seek in list lst,
   
5. 4 if seek is present in lst.
   
6. 5 Returns None if seek is not an element of lst.
   
7. 6 lst is the lst in which to search.
   
8. 7 seek is the element to find.
   
9. 8 '''
   
10. 9 for i in range(len(lst)):
    
11. 10 if lst[i] == seek:
    
12. 11 return i # Return position immediately
    
13. 12 return None # Element not found
    
14. 13
    
15. 14 def format(i):
    
16. 15 '''
    
17. 16 Prints integer i right justified in a 4-space
    
18. 17 field. Prints "****" if i > 9,999.
    
19. 18 '''
    
20. 19 if i > 9999:
    
21. 20 print("****") # Too big!
    
22. 21 else:
    
23. 22 print("%4d" % i)
    
24. 23
    
25. 24 def show(lst):
    
26. 25 '''
    
27. 26 Prints the contents of list lst
    
28. 27 '''
    
29. 28 for item in lst:
    
30. 29 print("%4d" % item, end='') # Print element right justifies in 4 spaces
    
31. 30 print() # Print newline
    
32. 31
    
33. 32 def draw_arrow(value, n):
    
34. 33 '''
    
35. 34 Print an arrow to value which is an element in a list.
    
36. 35 n specifies the horizontal offset of the arrow.
    
37. 36 '''
    
38. 37 print(("%" + str(n) + "s") % " ˆ ")
    
39. 38 print(("%" + str(n) + "s") % " | ")
    
40. 39 print(("%" + str(n) + "s%i") % (" +-- ", value))
    
41. 40
    
42. 41
    
43. 42 def display(lst, value):
    
44. 43 '''
    
45. 44 Draws an ASCII art arrow showing where
    
46. 45 the given value is within the list.
    
47. 46 lst is the list.
    
48. 47 value is the element to locate.
    
49. 
    
50. show(lst) # Print contents of the list
    
51. 50 position = locate(lst, value)
    
52. 51 if position != None:
    
53. 52 position = 4*position + 7; # Compute spacing for arrow
    
54. 53 draw_arrow(value, position)
    
55. 54 else:
    
56. 55 print("(", value, " not in list)", sep='')
    
57. 56 print()
    
58. 57
    
59. 58
    
60. 59 def main():
    
61. 60 a = [100, 44, 2, 80, 5, 13, 11, 2, 110]
    
62. 61 display(a, 13)
    
63. 62 display(a, 2)
    
64. 63 display(a, 7)
    
65. 64 display(a, 100)
    
66. 65 display(a, 110)
    
67. 66
    
68. 67 main()

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thanks  for sharing