What is the execution process of python for statement

The execution process of the python for statement: 1. Iterate through the sequence index, and the traversal method of executing the loop is through the index; 2. The statement in for is no different from the ordinary one, and the statement in else will be executed normally in the loop Executed when completed.

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Execution process of python for statement:

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

Grammar:

The syntax format of for loop is as follows:

for iterating_var in sequence:
   statements(s)

Flow chart:

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!"

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 sequence index

Another execution loop The traversal method is through index, as shown in the following 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!

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

Loop 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'

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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