I would say there is no Debian equivalent to Ubuntu's deadsnakes PPA

Under Debian, using Ubuntu packages or repositories is not recommended. As this post appears in search engines, I propose here an answer that is less dangerous for a Debian system.

Installing Python manually is possible. As an example, you can use the following instructions to install 3.5.2 version

Prerequisites

Install dependencies :

sudo apt-get update && sudo apt-get install libssl-dev openssl

Building Python

You can build Python in a specific folder using the --prefix parameter from configure command:

wget https://www.python.org/ftp/python/3.5.2/Python-3.5.2.tgz
tar zxf Python-3.5.2.tgz
cd Python-3.5.2/
./configure --prefix=/usr/local
make
sudo make install

Instead of /usr/local, one can use another base directory. As an example:

sudo mkdir /opt/python-3.5.2
./configure --prefix=/opt/python-3.5.2

Selecting python version

Using PATH environment variable can help choosing the right python version to use. But one can also use symlinks:

sudo ln -s /opt/python-3.5.2/bin/python3.5 /usr/local/bin/python3
sudo ln -s /opt/python-3.5.2/bin/pip3.5 /usr/local/bin/pip3

Using -f option will allow you to replace existing symlinks

Note: For python 3.9.16 (possibly any +3.9 version) you also might need to install the library: libffi-dev so the dependencies would be:

sudo apt-get update && sudo apt-get install libssl-dev openssl libffi-dev

As a rule a Linux system will depend, system-wide, on the Python version it was built with. In the case of Ubuntu 11.10 this is Python 2.7 - as you say.

dpkg (and friends) will default to installing for the default Python version set as follows:

1. symbolic link listed in the /etc/alternatives directory
2. the version that symbolic link /usr/bin/python is pointing at

like so:

$ ls -al /etc/alternatives | grep python
$ ls -al /usr/bin/python

You can temporarily change the default version of Python that your system utilities use by pointing the link to Python 2.6

$ sudo update-alternatives --config python

if Python 2.7 (or 2.6) does not display as choice then you have to first install it in the alternatives system. This is a guide.

Install the .deb package you built and then change the alternatives symbolic link back to the system's expected version:

$ sudo update-alternatives --config python

The subsystem that prescribes the Python version a Debian-based distro uses is discussed here

Felix Krull runs a PPA offering basically any version of Python (seriously, there is 2.3.7 build for vivid...) for many Ubuntu releases at https://launchpad.net/~deadsnakes/+archive/ubuntu/ppa.

Do the usual:

sudo add-apt-repository ppa:deadsnakes/ppa
sudo apt-get update
sudo apt-get install python3.5

It will not overwrite your existing python3.4 which is still symlinked as python3.

Instead, to run python3.5, run the command python3.5 (or python3.X for any other version of python).

DON'T change the symlink! There are apparently many system functions that don't work properly with python3.5.

I tried this and afterwards couldn't open a terminal, software updater,...

cd /usr/bin
sudo rm python3

The upgrade to Wily will adapt the meta-package python3 to point to python3.5. I don't expect any breakage, but at this point the foreign repository is not needed anymore. So to be really safe, you can purge the PPA before doing the upgrade.

I figured this out on ubuntu 20 in docker (I was running as root). If you are not running as root - this answer won't help you.

# update the package manager
apt-get update

# install git, C/C++ compiler and a text editor (I prefer vim)
apt install -y git software-properties-common curl build-essential vim

# add package source for python distributions
add-apt-repository ppa:deadsnakes/ppa

# install specific version of python with venv and distutils
apt install -y python3.9 python3.9-distutils python3.9-venv

# get pip
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
python3.9 get-pip.py

Python has got its own package managing facilities, in parallel to the one sets by the Linux distributions (including Ubuntu). The repository is the Pypi - Python Package Index, and packages are installed with pip or the easy_install script, which is part of Python's setuptools package.

As a rule of thumb, you should not use both the packages installed via pip/setuptools, and packages available to your distro (via apt-get, yum, urpmi, etc...) as they might conflict.

So, one of the less error prone way to deal with it is to have separate Python installs in your system - leave the python that came with the system for system scripts and such - on this python, make use of packages installed by your package manager only. And install other versions of Python (or even the same), to be run with "virtualenv"s - on these other install you install things with pip/setuptools only.

(And even if one opt to live boldly and not use virtualenvs, installing another python version on the same prefix (/usr, and even /usr/local) than your system's Python is a source to confusing errors and conflicts).

Note that the Debian - and Ubuntu - systems devised a way to run parallel official Python's in /usr, and to have apt-get to install Python packages to both Python versions at once. This mostly works, but they mess with Python's default directory hierarchy, and some applications fail to use Python in this way. (It is also a mess to find the module files themselves in a Debian or Ubuntu). So the above method apply as a recommendation even if your system do have more than one version of Python available on apt-get.

In short, once you have compiled your desired version of Python, do this:

1. use your system's package manager to install "python-setuptools" and "python-virtualenv" (not sure if these are the actual package names).
2. Use virtualenv to create an environment from which you will use your different Python version
3. Activate your virtualenv, and install Python packages using pip on it.

Virtualenv does feature a "--help" switch to help you, but you basically do:

Copy$ virtualenv -p <path-to-python-interpreter>  <environment-dir>
$ source <environment-dir>/bin/activate

And there you are - all things using Python will "see" the interpreter in the virtualenv, due to environment variables set.

Ok after a lot of searching I decided to build Python from source, so I downloaded the compressed source tarball from the Python download page, now we need to install the build-essential package to be able to compile the source files:

apt-get install build-essential

also we need to install these development packages which are required for some Python modules:

libbz2-dev
libsqlite3-dev
libreadline-dev
zlib1g-dev
libncurses5-dev
libssl-dev
libgdbm-dev

next we extract the downloaded source file:

tar zxf Python-2.7.6.tgz

then we cd into the extracted directory:

cd Python-2.7.6

and follow the instructions on the Python docs:

./configure --prefix=/opt/python
make
make install # <- in the docs but don't execute: use checkinstall

I chose to install it under the directory /opt/python which I created before, also I used the checkinstall package to create a .deb file so I can uninstall easily later, so we install it first:

apt-get install checkinstall

and substitute the last line make install with:

checkinstall

now I have a new python installation in /opt/python/lib/python2.7 and the binary file is in /opt/python/bin/python2.7.

now I can run in the command line /opt/python/bin/python2.7 to use this Python version, also we can make a link to this executable so we don't type the full path, I named it python2.7.6.

ln -s /opt/python/bin/python2.7 /usr/local/bin/python2.7.6

also the directory /opt/python/bin will contain later other executables like pip and virtualenv or any other modules you install so we can add it to the PATH environment variable, edit ~/.profile and add this line:

PATH="$PATH:/opt/python/bin"

and run:

source ~/.profile

I appended the path to the end because it contains executable names like the ones in /usr/bin like python, python2 and python2.7 so we keep the higher priority for /usr/bin.