python 循环语句
作用： 根据一定的条件，重复的执行一个或多个语句
两种循环语句：
while 语句
for 语句
while 语句：
语法：
while 真值表达式：
语句1
。。。
else：
语句2
。。。
语法说明： else子句可以省略
执行顺序： （1） 先判断真值表达式是否为True
（2）如果第1步为True，则执行语句1后跳到第1步，否则跳到第3步；
（3）执行else 子句
（4）结束 while 语句的执行
>>> n = 1
>>> while n <= 10 :
print(n)
n += 1
1
2
3
4
5
6
7
8
9
10
>>>
练习1 ：用字符串 * 运算符打印三角形；（要求输入一个整数，此整数代表三角形离左侧的字符串* 的距离）
n = int(input("请输入一个整数： "))
left = ‘ ‘ * n
print(left + ‘ *‘)
print(left + ‘ ***‘)
print(left + ‘ *****‘)
print(left + ‘*******‘)
>>> ================================ RESTART ================================
>>>
请输入一个整数： 3
*
***
*****
*******
>>> ================================ RESTART ================================
>>>
请输入一个整数： 0
*
***
*****
*******
>>>
练习2 输入三行文字，让三行文字在一个方框内居中显示（输入不要输入中文）；
1 #!/usr/bin/python
2
3 #输入3行文字
4 line1 = input("请输入第一行字符：")
5 line2 = input("请输入第二行字符：")
6 line3 = input("请输入第三行字符：")
7
8 #比较出3行中最大的一行字符长度
9 m = max(len(line1), len(line2), len(line3))
10
11 #使3行输出的文字居中
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 请输入第一行字符：aaaaaaaaaaaaa
20 请输入第二行字符：aaaaaaaa
21 请输入第三行字符：aaaaaaaaaa
22 +---------------+
23 | aaaaaaaaaaaaa |
24 | aaaaaaaa |
25 | aaaaaaaaaa |
26 +---------------+
27 >>>
while 语句嵌套
语法：
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 循环语句
for 语句可以用来遍历或者可迭代对象的每一个元素；
可迭代对象包括：
字符串str 、 列表list 、 元组tuple 、 字典dict 、 集合set 、 固定集合 frozenset 、 迭代器
for 语句的语法：
for 变量列表 in 可迭代对象
语句1
。。。。
else：
语句2
。。。。
说明： else子句部分可以省略 ； 语句1的执行次数与可迭代对象的元素个数有关；
#!/usr/bin/python
s = "Hello"
for i in s:
print("i->>", i)
else:
print("for 语句结束")
print("程序结束")
>>> ================================ RESTART ================================
>>>
i->> H
i->> e
i->> l
i->> l
i->> o
for 语句结束
程序结束
>>>
练习：任意输入一个字符串，计算输入的字符‘a’的个数，并打印出来；
原文地址：https://www.cnblogs.com/weizitianming/p/8969691.html
时间： 2024-08-03 01:41:12