Does python have a for loop?

for loop in Python

The Python for loop can traverse any sequence of items, such as a list or a string. (Traversal: In layman's terms, it means visiting the first element to the last element in this loop in sequence).

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.

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

Now let’s understand each line of code:

Line 1: Define a text_create function;

Line 2: Give the variable path Assign the value 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 file located in txt file 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 the 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.

 file = open('/Users/duwangdan/Desktop/test.txt')
 try:
     data = file.read()
 finally:
    file.close()

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

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

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

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

 for i in range(1,10):
    for j in range(1,10):
        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 in sequence j; finally print out the current values ​​of i, j, and i*j.

Starting from Python 2.6, the 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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