What's the best way to install two versions of python - python-2.7

Question

I want a easy and clean installation, in case a need to uninstall in future.
I'm running Sierra on my mac, currently I have a Anaconda 2.4 (with python 2.7) and now I need to use python 3.5 too. I looked to quite a few answers and the process seemed a little tricky to un-do if necessary.
Please, if possible, post also the uninstall process. Thanks.

Answer 1

Don't let the long answer intimidate you, the process can be resumed to 6 lines (really), but I tried to write the answer that I was looking for.
The option that suit me the best is virtualenv.
Installation
The simplest way is using brew:
brew install pyenv pyenv-virtualenv pyenv-virtualenvwrapper
to check the list of python versions we can use the command:
pyenv install -l
since I am interested in 3.5.1, I can easily install with the same command
pyenv install 3.5.1
Setup
Once installed, we can check the result using
$ pyenv versions
* system
3.5.1 (set by /Users/macbookpro/.pyenv/version)
this command list all versions installed, and indicates that I'm currently using system's version.
Before we change to 3.5.1 version we need to add pyenv path to .bash_profile.
In the file .bash_profile :
add the following lines. Pay attention if the PATH variable is the same in your case.
#added for pyenv
export PATH="/Users/macbookpro/.pyenv:$PATH"
eval "$(pyenv init -)"
eval "(pyenv virtualenv-init -)"
So now we have everything setup, let's test it
First, we check which version is currently in use:
$ pyenv versions
* system
3.5.1 (set by /Users/macbookpro/.pyenv/version)
Ok, now we know we have to change to 3.5.1. We can do it using:
$ pyenv global 3.5.1
$ python
Python 3.5.1 (default, Oct 20 2016, 21:43:48)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.38)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
We also verified that this is actually working. We now test the system version too.
$ pyenv global system
$ pyenv versions
* system (set by /Users/macbookpro/.pyenv/version)
3.5.1
$ python
Python 2.7.12 (default, Sep 5 2016, 20:55:16)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.38)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
Everything is working fine.
Uninstall
Simply :
$ rm -fr ~/.pyenv
And remove all the .bash_profile stuff that we added in setup.
Extras
For the Anaconda folk.
In jupyter :
In [1]: import sys
sys.version
Out [1]: '2.7.12 |Anaconda 4.1.1 (x86_64)| (default, Jul 2 2016, 17:43:17) \n[GCC 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)]'
Nothing changed.

Answer 2

The best way is to use virtualenv. It allows you to keep different working versions of python on the same machine without interfering with each other.
EDIT:
These are the instructions on how to install virtualenv on Mac OS.
Install the latest python version on your system:
brew install python (or python3)
Then using pip:
pip install virtualenv
Then in your home directory edit the .bashrc file. Create it if it doesn't exist. Add this line to the .bashrc file:
export PIP_REQUIRE_VIRTUALENV=true
The line above will make pip run only in virtual environment.
Apply the changes:
. .bashrc (if you in your home directory, note the dot and space before .bashrc file).
Now you should be able to use virtualenv.
If you in your project folder:
virtualenv some_venv
Then activate it:
. ./some_venv/bin/activate (note the dot).
Then you can install everything you need using pip. All the packages will go to the some_venv directory.
You want to deactivate the virtualenv, then run deactivate.
If you want to delete all the installed packages when you were under virutalenv, then just delete some_venv. That's it.
Regarding the pyenv. Honestly I have never used it. But there is an easy to follow tutorial on the github page of the project.
Hope it helps.