How to use for to repeat (loop) in python

Python is a scripting language. He has absorbed the essence of many languages ​​and has unique aspects. Among them, there are two types of loops in Python: for loop and while loop. In this article, I will give you a detailed introduction to using for loops to achieve certain repetitive operations.

The for loop can be used to traverse a certain object (traversal: in layman’s terms, it means to access the first element to the last element in this loop in sequence once).

The basic structure of the for loop is as follows:

Look at this case specifically:

Design one Function, create 10 texts on the desktop and name them with numbers from 1-10.

 1 def text_create(): 
 2     path = '/Users/duwangdan/Desktop/' 
 3     for text_name in range(1,11): 
 4         # 1-10的范围需要用到range函数 
 5         with open (path + str(text_name) + '.txt','w') as text: 
 6             # with...as的用法正文内会详细介绍 
 7             text.write(str(text_name)) 
 8             text.close() 
 9             print('Done')
 10
 11 text_create()

Now let’s understand each line of code.

Line 1: Define a text_create function;

Line 2: Assign the variable path to the desktop path ;

Line 3: Load each number in the range of 1-10 into the variable text_name in turn, naming one file at a time;

Line 5: Open the txt file located on the desktop and perform writing operations for each text;

Line 7: Name each file in turn;

Line 8: Close the file;

Line 9: Display a Done after performing a naming operation;

Line 11: Call function.

The case mentioned "with...as", In Python, the "with...as" syntax is used to replace the traditional "try...finally".

For example: open the test file on the desktop, try to read the file content, and finally close the file.

1 file = open('/Users/duwangdan/Desktop/test.txt')
2 try:
3     data = file.read()
4 finally:
5     file.close()

Although this code performs well, it is relatively verbose. If it is expressed using "with...as", the code will be more concise.

1 with open('/Users/duwangdan/Desktop/test.txt') as file:
2     data = file.read()

In addition to the single-layer loop above, there is also a common loop, which is nested loop.

For example, use nested loops to implement the multiplication formula.

1 for i in range(1,10):
2     for j in range(1,10):
3         print('{} X {} = {}'.format(i,j,i*j))

The outermost loop stores the numbers 1-9 in the variable i in sequence; every time the variable i takes a value, the inner loop stores the numbers 1-9 in the variable j in sequence; Finally, print out the current values ​​of i, j, and i*j.

Starting from Python 2.6, a new format function has been added to format strings, which can be achieved through {}.format. In the above case, the values ​​​​of i, j, and i*j are stored in the previous {} respectively, and then formatted to unify the form.

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