How to coexist with multiple versions of Python on Windows

1. If it is Windows, it is recommended to change the pip in the installation path to pip2 and pip3 respectively.
2. If it is Linux, the same method is used. Delete the soft link of pip and add pip2. Distinguish it from pip3 software. pip will automatically install the corresponding package

At present, domestic websites often ask people to change the name of one of the python.exe (well, I have said this too, and I will correct it here), so as to distinguish the two The name of the executable file, but there is a major hidden danger in doing so, that is, the pip corresponding to the python whose name has been modified will not be available.

What is the official solution?

In fact, the Python community provided an official solution to this problem a few years ago, but it has not been noticed in China.

When we install Python3 (>=3.3), the Python installation package actually installs a launcher py.exe in the system, which is placed under the folder C:\Windows\ by default . This launcher allows us to specify whether to use Python2 or Python3 to run the code (of course, the premise is that you have successfully installed Python2 and Python3).

For the installation of Python 2 and 3, please see the Python tribe (http://python.freelycode.com)- ->Audio and Video School-->The first section of "0 Basics 1 Hour, Introduction to Python".

If you have a Python file called hello.py, then you can run it with Python2 like this

py -2 hello .py

Similarly, if you want to run it with Python3, just like this

py -3 hello.py

Remove parameters -2/-3

It is still troublesome to add parameters -2/-3 every time you run it, so py.exe this The launcher allows you to add instructions to the code to indicate whether the file should be interpreted and run by python2 or python3. The method of explanation is to add a line

#! python2

or

# at the beginning of the code file.

! python3

respectively indicates that the code file is interpreted and run using Python2 or Python3. In this way, when running, your command can be simplified to

py hello.py

Use pip

When Python2 and Python3 exist on Windows at the same time, their corresponding pips are called pip.exe, so you cannot directly use the pip install command to install software packages. Instead, use the launcher py.exe to specify the version of pip. The command is as follows:

py -2 -m pip install XXXX

-2 still means using Python2, -m pip means running the pip module, That is, run the pip command. If you are installing software for Python3, the command will be similar to

py -3 -m pip install XXXX

#! Which one should be written first, python2 or #coding: utf-8?

There is another confusion for Python2 users. In Python2, you need to add a line of instructions at the top of the code file to be able to use Chinese in the code. If specifying the Python version to use also requires adding a line to the top of the file, which line should be placed first?

#! python2 needs to be placed on the first line, and the encoding instructions can be placed on the second line. So the beginning of the file should be similar to:

#! python2
# coding: utf-8

With these tips, Python2 and Python3 can happily play together~

Python standard: PEP 397 -- Python launcher for Windows