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pyenv global x.x.x does not update the python version on linux

I have pyenv installed and have downloaded python versions 3.6.15 and 3.7.12. When I run
pyenv global 3.7.12
python -V
the output is: Python 3.10.2
pyenv versions gives the output
system
3.6.15
* 3.7.12 (set by /home/frege/.pyenv/version)
$ echo $PYENV_ROOT: /home/frege/.pyenv
$ which python: /user/bin/python
$ type python: python is hashed (/usr/bin/python)
I have the following in my .bashrc
export PATH="${HOME}/.pyenv/bin:$PATH"
eval "$(pyenv init -)"
eval "$(pyenv virtualenv-init -)"
I have restarted my terminal and $PATH contains
/home/frege/.pyenv/plugins/pyenv-virtualenv/shims:
/home/frege/.pyenv/bin:
...
/usr/bin:
What is wrong?

I understand that getting pyenv and virtualenvs to work together can be problematic. I came from virtualenvwrapper which makes working on virtual envs simple and I found pyenv a bit of a culture shock.
I have finally got my workflow sorted and I thought I would post it here as it might help someone. My OS is Manjaro.
I installed pyenv:
curl https://pyenv.run | bash
The following was added to .bashrc:
export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/shims:${PATH}"
export PATH="$PYENV_ROOT/bin:$PATH"
export PYENV_VIRTUALENVWRAPPER_PREFER_PYVENV="true"
export WORKON_HOME=$HOME/.virtualenvs
eval "$(pyenv init -)"
pyenv virtualenvwrapper_lazy
(I have not seen the line export PATH="$PYENV_ROOT/shims:${PATH}" in many explanations, but it is critical in mine.)
To invoke a global version of python:
pyenv shell <version>
or
pyenv shell system
To create a virtual env:
pyenv virtualenv <version> <env name>
To activate the virtual environment:
pyenv activate <env name>
To deactivate the virtual environment:
source deactivate

pyenv: "python >virtual env name< not installed"

I am having trouble with pyenv after updating my macOS to 11.5. This is what I tried:
$ pyenv install 3.8.11 --skip-existing
$ pyenv virtualenv 3.8.11 >virtual env name<
$ pyenv local >virtual env name<
All of this works fine. Running pyenv local results in printing my virtual env's name. But I can't install dependancies or do anything with pip:
$ pip freeze
python >virtual env name< not installed
I tried following this answer, but I still have the same problem.
Note: This is also happening with virtual envs that were previously working pre-update.

Turns out the issue was with updating pyenv and not macOS. All I had to do was add the following lines to my ~./zshrc (or ~/.zprofile:
export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init --path)"

How install and use different versions of pythons on MacOS using pyenv

Starting out when I run $ which python3 I get:
/Library/Frameworks/Python.framework/Versions/3.8/bin/python3
And in my .zprofile I have:
PATH="/Library/Frameworks/Python.framework/Versions/3.8/bin:${PATH}"
export PATH
So starting out, I have 3.8 installed and it works. Now, I need to create a setup that will allow me to install and use different versions of python for different projects.
So, I tried the following:
$ brew update
$ brew install pyenv
$ pyenv version
It printed out System. So, it only sees the python 2.7 that comes with macos. Then I tried:
$ pyenv install 3.9.1
$ pyenv install 3.8.7
$ echo -e 'if command -v pyenv 1>/dev/null 2>&1; then\n eval "$(pyenv init -)"\nfi' >> ~/.zshrc
$ source ~/.zshrc
Now, at the end of my .zshrc file I have:
if command -v pyenv 1>/dev/null 2>&1; then
eval "$(pyenv init -)"
fi
But I still just get System when I run $ pyenv version. I know the different python versions are getting installed in ~/.pyenv/versions directory. So, what else am I supposed to do to get it
to list all the versions and switch back and forth between them?

First off, for pyenv to work correctly, you should uninstall the Python that's in /Library/Frameworks/Python.framework/Versions/3.8/bin/python3 and remove it from your $PATH.
If you use pyenv to manage your Python versions, then you should not install Python in any other way. pyenv will update your path automatically as you switch Python version.
Next, you need to set pyenv‘s default Python version by doing
$ pyenv global 3.9.1
on the command line.
Finally, to switch Python versions, you can use
$ pyenv local 3.8.7
on the command line. Note, that setting the local Python is sticky and works on a per-directory basis. So, for each directory where you need a specific Python version, use this command once.
For more info, see https://github.com/pyenv/pyenv/blob/master/COMMANDS.md

Virtual environment doesn't work on Cloud9

Cloud9 (an online ide) doesn't seem to support my virtual environment:
me:~/workspace/dir (master) $ source venv/bin/activate
(venv) me:~/workspace/dir (master) $ which python
/usr/bin/python
This same virtual directory worked fine on my local machine:
(venv) me$ which python
/Users/me/dir2/dir/venv/bin/python
How can I fix this?

The following works for me.
sudo apt-get install python3.5-venv
python3.5 -m venv --clear ./mypy3.5/
source ./mypy3.5/bin/activate
It uses the
(mypy3.5) $ which python
/home/ubuntu/mypy3.5/bin/python
But there is a gotcha which might have been your problem. The python3 -m venv uses soft links to how your python resolves in your environment. I had Python 3.3, 3.4 and 3.5 installed in /usr/local so the /usr/local/bin/python3 would change and break my Python3 venv. Note that "python3" is evaluated for the environment not for an absolute path. To be careful, when there are more than one Python 3 on you system, create your virtual environment with an explicit path like the following.
/usr/bin/python3.5 -m venv --clear ./mypy3.5/
source ./mypy3.5/bin/activate
ls -l $(which python3.5)
/home/ubuntu/mypy3.5/bin/python3.5 -> /usr/bin/python3.5*

How do I set Django to use Python 2.7 instead of the default Python 2.4?

I am using CentOS. The default python installed is 2.4 and I also installed 2.7 in order to use Django.
How can I configure Django to use /usr/local/bin/python2.7 instead of just the default python command?
I have to leave the default Python as 2.4 because other services such as yum don't run with 2.7.
Or is there other solution?

mod_wsgi is linked with specific version of Python. You have to recompile it with Python 2.7 and make Apache load new module (by editing file like /etc/apache2/mods-enabled/wsgi.load or /etc/apache2/modules.d/70_mod_wsgi.conf).
http://code.google.com/p/modwsgi/wiki/InstallationIssues

Just run this command into your command shell: python2.7 /path/to/manage.py runserver
Then Django will run under python 2.7

The answer is to use virtualenv to set up a virtual environment for python2.7 and to install your stuff into that sandbox.
Here is some code to get you going:
$ sudo apt-get install python-setuptools python-dev build-essential
$ sudo easy_install -U pip
$ sudo pip install virtualenv virtualenvwrapper
$ mkdir ~/.virtualenvs
$ sudo cat >> ~/.bashrc << EOF
# virtualenvwrapper setup
export WORKON_HOME=~/.virtualenvs
export VIRTUALENVWRAPPER_VIRTUALENV_ARGS='--no-site-packages --python=python2.7'
source /usr/local/bin/virtualenvwrapper.sh
EOF
$ source ~/.bashrc
$ mkvirtualenv test
$ pip install django
I am assuming that CentOS uses sudo like Ubuntu does. Substitute the native call if not.