Detailed explanation of three methods for importing custom modules in Python3

This article mainly introduces you to the three methods of importing custom modules in Python3. The article introduces it in detail through sample code, which has certain reference learning value for everyone's study or work

Preface

I recently learned the module section from Liao Xuefeng’s tutorial. Regarding how to customize a module, if you don’t understand, let’s take a look at the basic introduction first:

Module

In the development of computer programs In the process, as more program code is written, the code in a file will become longer and longer, making it increasingly difficult to maintain.

In order to write maintainable code, we group many functions and put them in different files. In this way, each file contains relatively less code. Many programming languages ​​​​adopt this organization of code. Way. In Python, a .py file is called a module.

What are the benefits of using modules?

The biggest benefit is that it greatly improves the maintainability of the code. Second, you don't have to start from scratch when writing code. When a module is written, it can be referenced elsewhere. When we write programs, we often refer to other modules, including Python's built-in modules and modules from third parties.

Using modules can also avoid conflicts between function names and variable names. Functions and variables with the same name can exist in different modules. Therefore, when we write the module ourselves, we do not have to consider that the name will conflict with other modules. But also be careful not to conflict with built-in function names. Click here to view all built-in functions of Python.

You may also think, what if different people write modules with the same name? In order to avoid module name conflicts, Python has introduced a method of organizing modules by directory, called a package.

For example, a file abc.py is a module named abc, and a file xyz.py is a module named xyz.

Now, suppose that our two module names abc and xyz conflict with other modules, so we can organize the modules through packages to avoid conflicts. The method is to choose a top-level package name, such as mycompany, and store it in the following directory:

mycompany
├─ __init__.py
├─ abc.py
└─ xyz.py

After the package is introduced, as long as the top-level package name does not conflict with others, all modules will not conflict with others. Now, the module name of abc.py becomes mycompany.abc, and similarly, the module name of xyz.py becomes mycompany.xyz.

Please note that there will be an __init__.py file under each package directory. This file must exist. Otherwise, Python will treat this directory as a normal directory instead of a package. __init__.py can be an empty file, or it can have Python code, because __init__.py itself is a module, and its module name is mycompany.

Similarly, there can be multi-level directories to form a multi-level package structure. For example, the following directory structure:

mycompany
├─ web
│ ├─ __init__.py
│ ├─ utils.py
│ └─ www.py
├ ─ __init__.py
├─ abc.py
└─ xyz.py

The module name of the file www.py is mycompany.web.www, and the module names of the two files utils.py are respectively are mycompany.utils and mycompany.web.utils.

When you create your own module, you should pay attention to the naming, and it cannot conflict with the module name that comes with Python. For example, if the system comes with the sys module, your module cannot be named sys.py, otherwise you will not be able to import the sys module that comes with the system.

mycompany.web is also a module. Please indicate the .py file corresponding to this module.

Summary

A module is a collection of Python codes that can use other modules and can also be used by other modules.

When creating your own module, please note:

• The module name must follow the Python variable naming convention and do not use Chinese or special characters;

• The module name should not conflict with the system module name. It is best to check whether the module already exists in the system. The check method is to execute import abc in the Python interactive environment. If it succeeds, it means that this module exists in the system.

Modules are a good thing. The experts share many modules in open source, which also speeds up everyone’s development.

Because I just started, I don’t understand many details, so on the Internet When searching for information, I found that the tutorials given by the experts were too concise, which made it very difficult for me, a novice, to succeed.

So record it here.

Start

The first way is to directly import

There is a major premise here, that is Your py execution file and module belong to the same directory (parent directory), as shown below:

• main.py and pwcong module are in the same directory python directory

• The execution file is main.py

• The pwcong folder is a module

I wrote the functions provided by the pwcong module in __init__.py, which only provides one hi function:

# pwcong 模块的 __init__.py
# -*- coding: utf-8 -*-
def hi():
 print("hi")

Execute the file main.py to directly import the module:

# main.py
# -*- coding: utf-8 -*-
import pwcong
pwcong.hi()

Then we run main.py and we can see that the command line window outputs the sentence hi. The first method is completed.

The way to use the module is: first import -》then enter the module.variable|function, such as pwcong.hi() in the above example

Second, import the path of the custom module through the sys module

If the executable file and the module are not in the same directory, the custom module cannot be found by direct import at this time. As shown below:

• The execution file main.py is in the main directory

• The pwcong module is in the python directory Next

The sys module is built-in in python, so the steps for us to import a custom module are as follows:

1. Import the sys module first

2. Then use the sys.path.append(path) function to import the directory where the custom module is located

3. Import the custom module.

At this time, write main.py like this:

# main.py
# -*- coding: utf-8 -*-
import sys
sys.path.append(r"C:\Users\Pwcong\Desktop\python")
import pwcong
pwcong.hi()

Finally execute the main.py file and finally output hi. The second method is completed.

The third method is to find the custom module through the pth file.

The principle of this method is to use system variables. Python will scan the path of the path variable to import the module. You can Add it to the system path. But I still recommend using pth file addition.

The module and executable file directory structure is the same as the picture:

• ##The executable file main.py is in the main directory

• The pwcong module is in the python directory

We create a module_pwcong.pth file, the content of which is the directory where the pwcong module is located:

C:\Users\Pwcong\Desktop\python

Put the module_pwcong.pth file here:

python installation directory\Python35\Lib\site-packages

For example, mine:

Then main.py imports and uses the custom module:

# -*- coding: utf-8 -*-
import pwcong
pwcong.hi()

Finally execute main.py File, you can output hi, the third way is completed.

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