Python中For循环与While 循环的使用

系统管理员 2023-01-07 11:29 152阅读 0赞

### Python中For循环与While 循环的使用 ###

*  For循环在枚举中使用：
 *  Continue和Break在For循环中的使用：
 *  举例：
 *  For 循环与While 循环区别：
 *  break语句在While 循环中使用：

For循环是迭代对象元素的常用方法，具有可迭代方法的任何对象都可以在for循环中使用。python的一个独特功能是代码块不被\{\} 或begin，end包围。相反，python使用缩进，块内的行必须通过制表符缩进，或相对于周围的命令缩进4个空格。

# For循环在枚举中使用： #

返回一个元组，其中包含每次迭代的计数（从默认为0开始）和迭代序列获得的值：

# For在枚举中使用：
    # 返回一个元组，其中包含每次迭代的计数（从默认为0开始）和迭代序列获得的值：
    friends = ['steve', 'rachel', 'michael', 'adam', 'monica']
    for index, friend in enumerate(friends):
        print(index,friend)

# Continue和Break在For循环中的使用： #

利用For循环：从下面文本中删除标点符号并将其转换为列表:

*  On a dark desert highway, cool wind in my hair Warm smell of colitas, rising up through the air Up ahead in the distance, I saw a shimmering light My head grew heavy and my sight grew dim I had to stop for the night There she stood in the doorway; I heard the mission bell And I was thinking to myself, “This could be Heaven or this could be Hell” Then she lit up a candle and she showed me the way

思路：

*  第一步：从文本中删除标点符（String中replace方法）
 *  第二步：将其转换为列表（Split函数：将String转换成list）

# 利用For循环：从文本中删除标点符号并将其转换为列表:（Continue在For循环中的使用：）
    text='''On a dark desert highway, cool wind in my hair Warm smell of colitas, rising up through the air Up ahead in the distance, I saw a shimmering light My head grew heavy and my sight grew dim I had to stop for the night There she stood in the doorway; I heard the mission bell And I was thinking to myself, "This could be Heaven or this could be Hell" Then she lit up a candle and she showed me the way'''
    print(text)
    
    #第一步：从文本中删除标点符，
    for char in '-.,;\n"\'':
        text = text.replace(char,' ')
    print(text)
    
    #第二步：将其转换为列表
    # Split converts string to list。Split函数：将String转换成list
    print('要将其转换为列表：',text.split(' ')[0:20])
    #法一：利用空格长度=0，去除列表中空格。
    # Each item in list is split on spaces
    # Dont want to have non words in my list for example ''
    # which in this case are things of zero length
    len('')
    # Making new list with no empty words in it
    cleaned_list = []
    for word in text.split(' '):
        word_length = len(word)
        if word_length > 0:
            cleaned_list.append(word)#不是空格，append追加
    print('利用For循环中if语句：',cleaned_list[0:20])
    
    #法二：利用Continue：
    # continue语句将转到循环的下一次迭代
    # continue语句用于忽略某些值，但不会中断循环
    cleaned_list = []
    
    for word in text.split(' '):
        if word == '':
            continue#如果是空格，不处理，继续for循环
        cleaned_list.append(word)
    print('利用For循环中continue',cleaned_list[0:20])

# for中Break的使用：
    # break语句将完全打断循环
    cleaned_list = []
    
    for word in text.split(' '):
        if word == 'desert':
            print('I found the word I was looking for')
            break
        cleaned_list.append(word)
    print(cleaned_list)

# 举例： #

编写一个Python程序，使用for循环迭代整数从1到50。对于偶数的整数，将其附加到列表even\_numbers；对于奇数的整数，将其附加到奇数奇数列表中。

# Making empty lists to append even and odd numbers to.
    even_numbers = []
    odd_numbers = []
    for number in range(1,51):
        if number%2==0:
            even_numbers.append(number)
        else:
            odd_numbers.append(number)
    print(even_numbers,"\n",odd_numbers)

# For 循环与While 循环区别： #

<table> 
 <thead> 
  <tr> 
   <th>For 循环</th> 
   <th>While 循环</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>遍历一组对象</td> 
   <td>条件为false时自动终止</td> 
  </tr> 
  <tr> 
   <td>没有break也可以结束</td> 
   <td>使用break语句才能退出循环</td> 
  </tr> 
 </tbody> 
</table>

# break语句在While 循环中使用： #

使用break可以完全退出循环

count = 0
    while count <= 5:
        if count == 2:
            break
        count += 1
        print (count)

x = 1
    while x % 5 != 0:
        x += 1
        print(x)