“笨办法”学Python 3 ——练习 33 While 循环

练习33 源代码

i = 0 #初始值
numbers = [] #用于存储的空列表

while i < 6 : #当i小于6时，布尔值为True，运行以下代码块
    print(f"At the top i is {i}") #打印while循环开头的变量
    numbers.append(i)
    
    i = i + 1
    print("Numbers now: ",numbers) #打印while循环结尾值
    print(f"At the bottom i is {i}") #打印while循环结尾值
    
print("The numbers: ")

for num in numbers: #for循环
    print(num)

输出结果

At the top i is 0
Numbers now:  [0]
At the bottom i is 1
At the top i is 1
Numbers now:  [0, 1]
At the bottom i is 2
At the top i is 2
Numbers now:  [0, 1, 2]
At the bottom i is 3
At the top i is 3
Numbers now:  [0, 1, 2, 3]
At the bottom i is 4
At the top i is 4
Numbers now:  [0, 1, 2, 3, 4]
At the bottom i is 5
At the top i is 5
Numbers now:  [0, 1, 2, 3, 4, 5]
At the bottom i is 6
The numbers: 
0
1
2
3
4
5

知识点：

1.while循环与for循环的区别？
Python中for循环和while循环本质上是没有区别的，都是去检查一个布尔表达式的真假，但是在实际应用上，针对性不太一样。
while循环适用于未知循环次数的循环，for循环适用于已知循环次数的循环 。
for主要应用在遍历中；而while循环很少进行遍历使用（语句过多，没有for方便），while主要用于判断符合条件下循环。
2. while循环运用
使用 while 循环，只要条件为真，我们就可以执行一组语句。
例如：
只要 i 小于 7，打印 i：

i = 1
while i < 7:
  print(i)
  i += 1

输出：

1
2
3
4
5
6

附加练习

1.把这个 while-loop 转换成一个你可以调用的函数，然后用一个变量替代 i < 6 里面的 6。&2.用这个函数重新写一下这个脚本，试试不同的数值。
代码如下：

def while_loop(a):
    numbers = [] #用于存储的空列表
    
    i = 0
    while i < a : #当i小于a时，布尔值为True，运行以下代码块
        print(f"At the top i is {i}") #打印while循环开头的变量
        numbers.append(i)
    
        i = i + 1
        print("Numbers now: ",numbers) #打印while循环结尾值
        print(f"At the bottom i is {i}") #打印while循环结尾值
    return numbers #返回number值,return与while平齐，不然无法执行while循环

a = int(input("The top of numbers is:"))
numbers = while_loop(a)
        
print("The numbers: ")
for num in numbers: #for循环
    print(num)

输出结果：
当变量a=8时：

The top of numbers is:8
At the top i is 0
Numbers now:  [0]
At the bottom i is 1
At the top i is 1
Numbers now:  [0, 1]
At the bottom i is 2
At the top i is 2
Numbers now:  [0, 1, 2]
At the bottom i is 3
At the top i is 3
Numbers now:  [0, 1, 2, 3]
At the bottom i is 4
At the top i is 4
Numbers now:  [0, 1, 2, 3, 4]
At the bottom i is 5
At the top i is 5
Numbers now:  [0, 1, 2, 3, 4, 5]
At the bottom i is 6
At the top i is 6
Numbers now:  [0, 1, 2, 3, 4, 5, 6]
At the bottom i is 7
At the top i is 7
Numbers now:  [0, 1, 2, 3, 4, 5, 6, 7]
At the bottom i is 8
The numbers: 
0
1
2
3
4
5
6
7

3. 再增加一个变量给这个函数的参数，然后改变第 8 行的 +1，让它增加的值与之前不同。&4.用这个函数重新写这个脚本，看看会产生什么样的效果。
输入代码：

def while_loop1(a,n): #定义2个参数，a为最大不超过的数值，n为步长
    numbers = [] #用于存储的空列表
    
    i = 0
    while i < a : #当i小于a时，布尔值为True，运行以下代码块
        print(f"At the top i is {i}") #打印while循环开头的变量
        numbers.append(i)
    
        i = i + n #每次循环i的步长为n
        print("Numbers now: ",numbers) #打印while循环结尾值
        print(f"At the bottom i is {i}") #打印while循环结尾值
    return numbers #返回number值,return与while平齐，不然无法执行while循环

b = int(input("The top of numbers is: "))
m = int(input("The step size is: "))

numbers = while_loop1(b,m)
for num in numbers:
    print(num)

输出结果：
number不超过10，第八行+1，更新为+2：

The top of numbers is: 10

The step size is: 2
At the top i is 0
Numbers now:  [0]
At the bottom i is 2
At the top i is 2
Numbers now:  [0, 2]
At the bottom i is 4
At the top i is 4
Numbers now:  [0, 2, 4]
At the bottom i is 6
At the top i is 6
Numbers now:  [0, 2, 4, 6]
At the bottom i is 8
At the top i is 8
Numbers now:  [0, 2, 4, 6, 8]
At the bottom i is 10
0
2
4
6
8

5.用 for-loop 和 range 写这个脚本。你还需要中间的增加值吗？如果不去掉这个增加值会发生什么？
用for—loop不需要使用中间增加值，代码如下：

numbers = []

for i in range(0,6):
    print(f"At the top i is {i}") #打印while循环开头的变量
    numbers.append(i)
    print("Numbers now: ",numbers) #打印while循环结尾值

print("The numbers: ")

for num in numbers: #for循环
    print(num)

输出结果：

At the top i is 0
Numbers now:  [0]
At the top i is 1
Numbers now:  [0, 1]
At the top i is 2
Numbers now:  [0, 1, 2]
At the top i is 3
Numbers now:  [0, 1, 2, 3]
At the top i is 4
Numbers now:  [0, 1, 2, 3, 4]
At the top i is 5
Numbers now:  [0, 1, 2, 3, 4, 5]
The numbers: 
0
1
2
3
4
5

若不去掉增加值，numbers列表结果不变，循环时并不会引用i=i+1的值，但是At the bottom i is 的值是i=i+1，代码如下：

numbers = []

for i in range(0,6):
    print(f"At the top i is {i}") #打印while循环开头的变量
    numbers.append(i)
    print("Numbers now: ",numbers) #打印while循环结尾值
    #若不去掉增加值
    i = i+1
    print(f"At the bottom i is {i}") #打印while循环结尾值

print("The numbers: ")

for num in numbers: #for循环
    print(num)

输出结果：

At the top i is 0
Numbers now:  [0]
At the bottom i is 1
At the top i is 1
Numbers now:  [0, 1]
At the bottom i is 2
At the top i is 2
Numbers now:  [0, 1, 2]
At the bottom i is 3
At the top i is 3
Numbers now:  [0, 1, 2, 3]
At the bottom i is 4
At the top i is 4
Numbers now:  [0, 1, 2, 3, 4]
At the bottom i is 5
At the top i is 5
Numbers now:  [0, 1, 2, 3, 4, 5]
At the bottom i is 6
The numbers: 
0
1
2
3
4
5

常见问题

1. for-loop 和 while-loop 的区别是什么？ for-loop 只能迭代（循环）一些东西的集合，而 while-loop 能够迭代（循环）任何类型的东西。不过，while-loop 很难用对，而你通常能够用 for-loop 完成很多事情。（同知识点1）