Isn't it easy to learn Python circles with old Qi ?, Qi xue python circle

Isn't it easy to learn Python circles with old Qi ?, Qi xue python circle

In python, a loop has a statement: for statement.

Simple for loop example

>>> hello = "world">>> for i in hello:...   print i... world

How does the above for loop work?

Hello, this variable references data of the str type "world ".
Variable I uses hello to locate the referenced "world", and then obtains the reference from the first character.
When I = "w", execute print I, print out the letter w, and then loop for the second time, let I = "e", then execute print I, print the letter e. The loop continues until the last character is printed, and the loop ends automatically.
By the way, I would like to add a print technique. The print result above is arranged vertically, that is, the line feed is automatically generated after each print. If you want to print a row, you can use the following method to add a comma after the print)

>>> For I in hello :... print I ,... w o r l d >>> for I in hello :... print I + ",", # to be beautiful, you can add a comma after each character to separate... w, o, r, l, d, >>>

Because you can use the index number (offset) as the following table to obtain a character. Therefore, you can implement the same functions in the above Code through the following loop:

>>> for i in range(len(hello)):...   print hello[i]... world

The working method is as follows:

Len (hello) gets the length of the string referenced by hello, which is 5
Range (len (hello), that is, range (5), that is, [0, 1, 2, 3, 4], corresponds to the number of each letter of "world", that is, the offset.
For I in range (len (hello) is equivalent to for I in [, 4], so that I is equal to the values in the list in turn. When I = 0, print hello [0], that is, the first character. Then it repeats sequentially until the last I = 4.
In the preceding loop example, the str character is obtained in sequence and the list is involved. Well, let's take a look at the list loop:

>>> ls_line['Hello', 'I am qiwsir', 'Welcome you', '']>>> for word in ls_line:...   print word... HelloI am qiwsirWelcome you>>> for i in range(len(ls_line)):...   print ls_line[i]... HelloI am qiwsirWelcome you

Last step

We have understood the basic workflow of the for statement. If you write a general formula, it can be expressed as follows:

For target in object:
Operation statement
Use the for statement to solve a problem.

For example, a positive integer smaller than 100 that can be divisible by 3 is found.

Analysis: There are two restrictions on this problem. The first is a positive integer within 100. According to the previous study, range (1,100) can be used for implementation. The second is to solve the problem of being divisible by 3, suppose a positive integer n. If this number can be divisible by 3, that is, n % 3 (% is the remainder) is 0. so how to get n is to use the for loop.

The above is a simple analysis, and the process needs to be further detailed. Follow the previous method to draw a flowchart for solving the problem.

Write the following code as shown in the following figure.

Code:

#! /usr/bin/env python#coding:utf-8aliquot = []for n in range(1,100):  if n%3 == 0:    aliquot.append(n)print aliquot

Code running result:

[3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 72, 75, 78, 81, 84, 87, 90, 93, 96, 99]
Here is just a simple example. You can go deep into this example to print even numbers/odd numbers in a certain range.