[Django]-How to switch Python versions in Terminal?

As Inian suggested, you should alias python to point to python 3. It is very easy to do, and very easy to switchback, personally i have an alias setup for p2=python2 and p3=python3 as well to save on keystrokes.
Read here for more information: How do I create a Bash alias?

Here is an example of doing so for python:

alias python=python3

Like so:

$ python --version
Python 2.7.6
$ python3 --version
Python 3.4.3
$ alias python=python3
$ python --version
Python 3.4.3

See here for the original:
https://askubuntu.com/questions/320996/how-to-make-python-program-command-execute-python-3

pyenv is a 3rd party version manager which is super commonly used (18k stars, 1.6k forks) and exactly what I looked for when I came to this question.

edit: I use it for several years now. Works like a charm.

Installation

Install pyenv.

Usage

$ pyenv install --list
Available versions:
  2.1.3
  [...]
  3.8.1
  3.9-dev
  activepython-2.7.14
  activepython-3.5.4
  activepython-3.6.0
  anaconda-1.4.0
  [... a lot more; including anaconda, miniconda, activepython, ironpython, pypy, stackless, ....]

$ pyenv install 3.8.1
Downloading Python-3.8.1.tar.xz...
-> https://www.python.org/ftp/python/3.8.1/Python-3.8.1.tar.xz
Installing Python-3.8.1...
Installed Python-3.8.1 to /home/moose/.pyenv/versions/3.8.1

$ pyenv versions
* system (set by /home/moose/.pyenv/version)
  2.7.16
  3.5.7
  3.6.9
  3.7.4
  3.8-dev

$ python --version
Python 2.7.17
$ pip --version
pip 19.3.1 from /home/moose/.local/lib/python3.6/site-packages/pip (python 3.6)

$ mkdir pyenv-experiment && echo "3.8.1" > "pyenv-experiment/.python-version"
$ cd pyenv-experiment

$ python --version
Python 3.8.1
$ pip --version
pip 19.2.3 from /home/moose/.pyenv/versions/3.8.1/lib/python3.8/site-packages/pip (python 3.8)

You can just specify the python version when running a program:

for python 2:

python filename.py

for python 3:

python3 filename.py

You can open and use zsh terminal on Mac OS.

Edit file /Users/{your_username}/.zshrc using nano or vim.

Add new alias for python 3

alias python="python3"

Save and check your python version using this following command.

python --version

Look at the result:

If you have python various versions of python installed,you can launch any of them using pythonx.x.x where x.x.x represents your versions.

I have followed the below steps on a MacBook.

1. Open the terminal.
2. Type nano ~/.bash_profile and enter. (Or vim instead of nano if you use vim.)
3. Now add the line alias python=python3
4. Press CTRL + x then y to save it. (Or just save it on vim since you can’t exit vim.)
5. It will prompt for the file name, simply hit enter.
6. Now check the python version by using the command: python –version
7. If you see 2.0.0+, it worked!

Adding to Inian’s answer (Accepted one),

• To check python 3 version

python3 -V

• To switch to new version of python which is already installed (eg. 3.7 to 3.9)

alias python="python3.9"

• To install new version of python, you can use homebrew on MAC

• Once homebrew is installed, you can install new python version with
  homebrew

brew install python@3.9

and then switch to this new version using

alias python="python3.9"

• Check python version to confirm the change

• To check all the installed versions of python

brew list | grep python

Here is a nice and simple way to do it (but on CENTOS), without braking the operating system.

yum install scl-utils

next

yum install centos-release-scl-rh

And lastly you install the version that you want, lets say python3.5

yum install rh-python35

And lastly:

scl enable rh-python35 bash

Since MAC-OS is a unix operating system, the way to do it it should be quite similar.

I am a beginner in python and was looking for the same and in the terminal, I just typed python3 and it came up with the newest version. I am thinking that if one wants to go to a different version they can just type that in? Could be wrong but this is what shows up when I typed python3.

% python3
Python 3.9.2 (v3.9.2:1a79785e3e, Feb 19 2021, 09:06:10) 
[Clang 6.0 (clang-600.0.57)] on darwin

Before when I just typed python. This is the message I would get.

% python2.7
WARNING: Python 2.7 is not recommended. 
This version is included in macOS for compatibility with legacy software. 
Future versions of macOS will not include Python 2.7. 
Instead, it is recommended that you transition to using 'python3' from within Terminal.
Python 2.7.16 (default, Jun  5 2020, 22:59:21) 
[GCC 4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.29.20) (-macos10.15-objc- on darwin
Type "help", "copyright", "credits" or "license" for more information.

In order to easily manage the different python versions. Please use below link to see how to use the versions effectively and without any environment variables.
https://youtu.be/jTN4MHNhJZs

ON WINDOWS HOWEVER…

sometimes you could just rename the file to "python3" in a python 3 enviroment
the program itself will still work but some ides will break for obvious reasons…
so my answer works on windows but it makes ides that dont have support for enviroments break

why am i the only windows user to mention this

On windows you can use conda

1- install conda Link to install

2- install required py version with conda

conda create --name py=3.8 python=3.8
:: conda create --name <env_name> python=<version>

3- init the terminal that you are using

conda init powershell
:: conda init <something>

4- Now you switch to any version dedfined on step 2 .

python --version
:: output current version for eg python 2.7
conda activate py=3.8
python --version
:: output  python 3.8