How to write a for loop statement in python

How to write a for loop statement in python?

Python for loop statement

Python for loop can traverse any sequence of items, such as a list or a string.

The syntax format of the for loop is as follows:

for iterating_var in sequence:
   statements(s)

Example

#!/usr/bin/python
# -*- coding: UTF-8 -*-
 
for letter in 'Python':     # 第一个实例
   print '当前字母 :', letter
 
fruits = ['banana', 'apple',  'mango']
for fruit in fruits:        # 第二个实例
   print '当前水果 :', fruit
 
print "Good bye!"

The output result of the above example:

当前字母 : P
当前字母 : y
当前字母 : t
当前字母 : h
当前字母 : o
当前字母 : n
当前水果 : banana
当前水果 : apple
当前水果 : mango
Good bye!

Iterate through the sequence index

Another way to execute loop traversal is through index, as shown in the following example:

Example

#!/usr/bin/python
# -*- coding: UTF-8 -*-
 
fruits = ['banana', 'apple',  'mango']
for index in range(len(fruits)):
   print '当前水果 :', fruits[index]
 
print "Good bye!"

The output result of the above example:

当前水果 : banana
当前水果 : apple
当前水果 : mango
Good bye!

For the above example we The built-in functions len() and range() are used. The function len() returns the length of the list, that is, the number of elements. range returns a sequence of numbers.

Looping using else statements

In python, for...else means this. The statements in for are no different from ordinary ones. The statements in else will be in It is executed when the loop is executed normally (that is, for is not interrupted by break), and the same is true for while...else.

Example

#!/usr/bin/python
# -*- coding: UTF-8 -*-
 
for num in range(10,20):  # 迭代 10 到 20 之间的数字
   for i in range(2,num): # 根据因子迭代
      if num%i == 0:      # 确定第一个因子
         j=num/i          # 计算第二个因子
         print '%d 等于 %d * %d' % (num,i,j)
         break            # 跳出当前循环
   else:                  # 循环的 else 部分
      print num, '是一个质数'

The output result of the above example:

10 等于 2 * 5
11 是一个质数
12 等于 2 * 6
13 是一个质数
14 等于 2 * 7
15 等于 3 * 5
16 等于 2 * 8
17 是一个质数
18 等于 2 * 9
19 是一个质数

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