The Road to Python, Part 4: Introduction and Basics of Python 5

python loop statement

             Function: Repeatedly execute one or more statements according to certain conditions

            Two loop statements:

                    while statement

                    for statement

            while statement:

                   grammar:

                   while truth expression:

                           Statement 1

                           。。。

                   else：

                            Statement 2

                            。。。

                   Syntax description: else clause can be omitted

                  Execution order: (1) First determine whether the truth expression is True

                                    (2) If step 1 is True, execute statement 1 and skip to step 1, otherwise skip to step 3;

                                    (3) Execute the else clause

                                    (4) End the execution of the while statement

>>> n = 1
>>> while n <= 10 :
    print(n)
    n += 1

    
1
2
3
4
5
6
7
8
9
10
>>>

 

 

      Exercise 1: Print the triangle with the string * operator; (requires an integer representing the distance of the triangle from the string * on the left)

n = int(input( " Please enter an integer: " ))
left = ' ' * n
print(left + '   *')
print(left + '  ***')
print(left + ' *****')
print(left + '*******')

>>> ================================ RESTART ================================
>>>  
Please enter an integer: 3
      *
     ***
    *****
   *******
>>> ================================ RESTART ================================
>>> 
Please enter an integer: 0
   *
  ***
 *****
*******
>>>

 

        Exercise 2 Enter three lines of text, and let the three lines of text be centered in a box (do not enter Chinese);

1  # !/usr/bin/python 
2  
3  #Enter 3 lines of text 
4 line1 = input( " Please enter the first line of characters: " )
 5 line2 = input( " Please enter the second line of characters: " )
 6 line3 = input ( " Please enter the third line of characters: " )
 7  
8  #Compare the length of the largest line of characters in the 3 lines 
9 m = max(len(line1), len(line2), len(line3))
 10  
11  #Make 3 lines Center the output text 
12  print ( ' + ' + ' - ' * ( m + 2 ) + '+')
13 print('| ' + line1.center(m) + ' |')
14 print('| ' + line2.center(m) + ' |')
15 print('| ' + line3.center(m) + ' |')
16 print('+' + '-' * ( m + 2 ) + '+')
17>>> ================================= RESTART =============== =================
 18 >>> 
 19  Please enter the first line of characters: aaaaaaaaaaaaa
 20  Please enter the second line of characters: aaaaaaaa
 21  Please enter the third line of characters: aaaaaaaaaa
 22 +---------------+
 23 | aaaaaaaaaaaaa |
 24 | aaaaaaaa |
 25 | aaaaaaaaaa |
 26 +---------------+
 27 >> >

 

                 while statement nesting

                         grammar:

                         while   a > b:

                               while  b > c:

                                      ......

                          else:

                                 .......

 1 >>> i = 1
 2 >>> while i < 10:
 3     j = 1
 4     while j < 10:
 5         print("i =", i, "j =", j)
 6         j += 1
 7     i += 1
 8 
 9     
10 i = 1 j = 1
11 i = 1 j = 2
12 i = 1 j = 3
13 i = 1 j = 4
14 i = 1 j = 5
15 i = 1 j = 6
16 i = 1 j = 7
17 i = 1 j = 8
18 i = 1 j = 9
19 i = 2 j = 1
20 i = 2 j = 2
21 i = 2 j = 3
22 i = 2 j = 4
23 i = 2 j = 5
24 i = 2 j = 6
25 i = 2 j = 7
26 i = 2 j = 8
27 i = 2 j = 9
28 i = 3 j = 1
29 i = 3 j = 2
30 i = 3 j = 3
31 i = 3 j = 4
32 i = 3 j = 5
33 i = 3 j = 6
34 i = 3 j = 7
35 i = 3 j = 8
36 i = 3 j = 9
37 i = 4 j = 1
38 i = 4 j = 2
39 i = 4 j = 3
40 i = 4 j = 4
41 i = 4 j = 5
42 i = 4 j = 6
43 i = 4 j = 7
44 i = 4 j = 8
45 i = 4 j = 9
46 i = 5 j = 1
47 i = 5 j = 2
48 i = 5 j = 3
49 i = 5 j = 4
50 i = 5 j = 5
51 i = 5 j = 6
52 i = 5 j = 7
53 i = 5 j = 8
54 i = 5 j = 9
55 i = 6 j = 1
56 i = 6 j = 2
57 i = 6 j = 3
58 i = 6 j = 4
59 i = 6 j = 5
60 i = 6 j = 6
61 i = 6 j = 7
62 i = 6 j = 8
63 i = 6 j = 9
64 i = 7 j = 1
65 i = 7 j = 2
66 i = 7 j = 3
67 i = 7 j = 4
68 i = 7 j = 5
69 i = 7 j = 6
70 i = 7 j = 7
71 i = 7 j = 8
72 i = 7 j = 9
73 i = 8 j = 1
74 i = 8 j = 2
75 i = 8 j = 3
76 i = 8 j = 4
77 i = 8 j = 5
78 i = 8 j = 6
79 i = 8 j = 7
80 i = 8 j = 8
81 i = 8 j = 9
82 i = 9 j = 1
83 i = 9 j = 2
84 i = 9 j = 3
85 i = 9 j = 4
86 i = 9 j = 5
87 i = 9 j = 6
88 i = 9 j = 7
89 i = 9 j = 8
90 i = 9 j = 9
91 >>> 

 

            for loop statement

                   The for statement can be used to traverse or iterable each element of an object;

                  Iterable objects include:

                       string str , list list , tuple tuple , dictionary dict , set set , fixed set frozenset , iterator

                   The syntax of the for statement:

                          for variable list in iterable object

                                 Statement 1

                                 。。。。

                          else：

                                 Statement 2

                                   。。。。

                           Note: The else clause part can be omitted; The number of executions of statement 1 is related to the number of elements of the iterable object;