Krdytkyu

Unless you really have a burning desire to compile it yourself, the preferred way is to use the DeadSnakes PPA to install versions of Python that aren't included by default:

sudo add-apt-repository ppa:deadsnakes/ppa

sudo apt-get update

sudo apt-get install python2.7

Other versions, such as python2.4 or python3.6, etc. are also available.

Continuing to document this for the latest Ubuntu releases¹ : for Ubuntu 16.04.1 server, the default Python is version 3.5, and Python 2.7 is not installed by default. On a fresh install (note that there's not even a python executable):

$ type python3 python2 python 

python3 is /usr/bin/python3

-bash: type: python2: not found

-bash: type: python: not found



$ python3 --version 

Python 3.5.2



$ python --version 

The program 'python' can be found in the following packages:

 * python-minimal

 * python3

Try: sudo apt install <selected package>

Note: before continuing, you will probably want to do a quick sudo apt-get update, sudo apt-get upgrade, and sudo apt-get dist-upgrade (please do note exactly what these commands are in fact doing; I'm assuming a fresh install here.)

Installing python 2.7 is as easy as:

$ sudo apt-get install python2.7

The initial output of installing python 2.7 is as follows:

$ sudo apt-get install python2.7

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following additional packages will be installed:

  libpython2.7-minimal libpython2.7-stdlib python2.7-minimal

Suggested packages:

  python2.7-doc binutils binfmt-support

The following NEW packages will be installed:

  libpython2.7-minimal libpython2.7-stdlib python2.7 python2.7-minimal

0 upgraded, 4 newly installed, 0 to remove and 0 not upgraded.

Need to get 3,735 kB of archives.

After this operation, 15.8 MB of additional disk space will be used.

Do you want to continue? [Y/n] Y

...etc, etc...

After installing python 2.7,

$ type python3 python2.7 python3.5 python2 python

python3 is /usr/bin/python3

python2.7 is /usr/bin/python2.7

python3.5 is /usr/bin/python3.5

bash: type: python2: not found

bash: type: python: not found

But there's still a problem, since you can't yet install PyPI modules via pip -- e.g., if you want jupyter notebook, or the latest scipy or numpy (etc), you'll want to install pip and then pip install those, and still turning to apt-get to install any needed system dependencies, like graphviz or core system libraries.

$ type pip3 pip2 pip

bash: type: pip3: not found

bash: type: pip2: not found

bash: type: pip: not found



$ python3 -m pip --version 

/usr/bin/python3: No module named pip

So to install pip, again, it's as easy as sudo apt-get install python-pip :

$ sudo apt-cache search -n pip | egrep '^python[0-9]*-pip'

python-pip - alternative Python package installer

python-pip-whl - alternative Python package installer

python3-pip - alternative Python package installer - Python 3 version of the package

You'll need both python-pip for the Python 2.7 pip and the python3-pip for the Python 3 pip. The installation via apt-get is sure to install the required dependencies; e.g, here's the output for installing pip2:

$ sudo apt-get install python-pip

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following additional packages will be installed:

  binutils build-essential dpkg-dev fakeroot g++ g++-5 gcc gcc-5 libalgorithm-diff-perl

  libalgorithm-diff-xs-perl libalgorithm-merge-perl libasan2 libatomic1 libc-dev-bin libc6-dev

  libcc1-0 libcilkrts5 libdpkg-perl libexpat1-dev libfakeroot libfile-fcntllock-perl libgcc-5-dev

  libgomp1 libitm1 liblsan0 libmpx0 libpython-all-dev libpython-dev libpython-stdlib libpython2.7

  libpython2.7-dev libquadmath0 libstdc++-5-dev libtsan0 libubsan0 linux-libc-dev make

  manpages-dev python python-all python-all-dev python-dev python-minimal python-pip-whl

  python-pkg-resources python-setuptools python-wheel python2.7-dev

Suggested packages:

  binutils-doc debian-keyring g++-multilib g++-5-multilib gcc-5-doc libstdc++6-5-dbg gcc-multilib

  autoconf automake libtool flex bison gdb gcc-doc gcc-5-multilib gcc-5-locales libgcc1-dbg

  libgomp1-dbg libitm1-dbg libatomic1-dbg libasan2-dbg liblsan0-dbg libtsan0-dbg libubsan0-dbg

  libcilkrts5-dbg libmpx0-dbg libquadmath0-dbg glibc-doc libstdc++-5-doc make-doc python-doc

  python-tk python-setuptools-doc

The following NEW packages will be installed:

  binutils build-essential dpkg-dev fakeroot g++ g++-5 gcc gcc-5 libalgorithm-diff-perl

  libalgorithm-diff-xs-perl libalgorithm-merge-perl libasan2 libatomic1 libc-dev-bin libc6-dev

  libcc1-0 libcilkrts5 libdpkg-perl libexpat1-dev libfakeroot libfile-fcntllock-perl libgcc-5-dev

  libgomp1 libitm1 liblsan0 libmpx0 libpython-all-dev libpython-dev libpython-stdlib libpython2.7

  libpython2.7-dev libquadmath0 libstdc++-5-dev libtsan0 libubsan0 linux-libc-dev make

  manpages-dev python python-all python-all-dev python-dev python-minimal python-pip

  python-pip-whl python-pkg-resources python-setuptools python-wheel python2.7-dev

0 upgraded, 49 newly installed, 0 to remove and 0 not upgraded.

Need to get 61.1 MB of archives.

After this operation, 169 MB of additional disk space will be used.

Do you want to continue? [Y/n] Y

...etc...

An interesting thing happens as a result of this: you now have the "standard" (and PEP recommended) python2 and python3 (which are just symlinks to python 2.7 and python 3.5):

$ type python3 python2 python python2.7 python3.5 

python3 is /usr/bin/python3

python2 is /usr/bin/python2

python is /usr/bin/python

python2.7 is /usr/bin/python2.7

python3.5 is /usr/bin/python3.5

You'll also want to sudo apt-get install python3-pip; before you install, you have:

$ type pip pip2 pip3

pip is /usr/bin/pip

pip2 is /usr/bin/pip2

-bash: type: pip3: not found



$ python2 -m pip --version 

pip 8.1.1 from /usr/lib/python2.7/dist-packages (python 2.7)



$ python3 -m pip --version 

/usr/bin/python3: No module named pip

After installing pip3,

$ sudo apt-get install python3-pip

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following additional packages will be installed:

  libpython3-dev libpython3.5-dev python3-dev python3-setuptools python3-wheel python3.5-dev

Suggested packages:

  python-setuptools-doc

The following NEW packages will be installed:

  libpython3-dev libpython3.5-dev python3-dev python3-pip python3-setuptools python3-wheel python3.5-dev

0 upgraded, 7 newly installed, 0 to remove and 0 not upgraded.

Need to get 38.0 MB of archives.

After this operation, 55.2 MB of additional disk space will be used.

Do you want to continue? [Y/n] 

...etc...

The resulting versions:

$ type python python2 python3 pip pip2 pip3

python is /usr/bin/python

python2 is hashed (/usr/bin/python2)

python3 is hashed (/usr/bin/python3)

pip is /usr/bin/pip

pip2 is /usr/bin/pip2

pip3 is /usr/bin/pip3



$ pip --version 

pip 8.1.1 from /usr/lib/python2.7/dist-packages (python 2.7)



$ pip3 --version 

pip 8.1.1 from /usr/lib/python3/dist-packages (python 3.5)



$ python2 -m pip --version 

pip 8.1.1 from /usr/lib/python2.7/dist-packages (python 2.7)



$ python3 -m pip --version 

pip 8.1.1 from /usr/lib/python3/dist-packages (python 3.5)

And one last thing before you can go and start installing all your favorite python PyPI modules: you'll probably have to upgrade pip itself (both pip2 and pip3, separately; also, it doesn't matter if pip is invoked via the python executables or the pip executables, the actual upgrades are stored in /usr/lib):

$ sudo -H python2 -m pip install --upgrade pip

...

$ sudo -H python3 -m pip install --upgrade pip

...

You can now run either the stand-alone pip or the version bundled within python (via python -m pip {command}).

[1] Historical recap: older Ubuntu had only Python 2.6, thus all the various methods to get Python 2.7+ installed. Later, after Python 2.7 was added to the public repositories, we still had the same challenge to install the newest Python 2.7 with latest fixes, which was (too) frequently necessary. The situation today is much better/simpler: the current Python 2.7 & 3.5 (basically the only two Python platform versions people care about) that are now in the public repos are very stable, so now we really only have to worry about installing the latest python modules, not the latest python. So now the Python "latest version problem" has moved partly out of the OS repos & apt and into PyPI & pip.)

12.04

If you are following Achu's answer, then the term libread5-dev should be changed to libreadline-gplv2-dev. So the full command would be:

sudo apt-get install libreadline-gplv2-dev libncursesw5-dev libssl-dev libsqlite3-dev tk-dev libgdbm-dev libc6-dev libbz2-dev

You can also download and install it via pyenv

#Install Pyenv

git clone https://github.com/pyenv/pyenv.git ~/.pyenv

export PATH=~/.pyenv/bin:/usr/local/hadoop/bin/:$PATH

echo 'export PYENV_ROOT="~/.pyenv"' >> ~/.bash_profile

echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.bash_profile

echo 'eval "$(pyenv init -)"' >> ~/.bash_profile



#Install Python

pyenv install 2.7.8

pyenv global 2.7.8



pyenv install 3.4.5

pyenv global 3.4.5

^{_{Mostly a mirror of this answer with a tweaked intro}}

I would recommend pyenv. It automates the build process aside from installing the header dependencies (see below). You can build and install a new (or old) version of Python by simply saying pyenv install 3.6.0. Everything runs as your user, so you don't have to worry about messing up the Python used by Ubuntu itself.

As opposed to some of the apt-repo-based options (e.g. deadsnakes), it will generally work same day of a release after a pyenv update because you don't need to wait for someone else to package it. See all the versions you can install with pyenv install --list

Install pyenv

1. 
   

   Install tools and headers needed to build CPythons (exotic Pythons like PyPy or Jython may have other dependencies). Git is used by pyenv, plus it also enables builds/installs of source branches, so you could install whatever 3.8 is right now, i.e. the master branch of CPython fresh off GitHub:

   
   
   

   sudo apt-get install -y git
   
   sudo apt-get install -y build-essential libbz2-dev libssl-dev libreadline-dev 
   
                           libffi-dev libsqlite3-dev tk-dev
   
   
   
   # optional scientific package headers (for Numpy, Matplotlib, SciPy, etc.)
   
   sudo apt-get install -y libpng-dev libfreetype6-dev    
   
   

   
   


2. 
   

   Run the installer script (installs pyenv and some very useful pyenv plugins by the original author; see here for more)

   
   
   

   curl -L https://github.com/pyenv/pyenv-installer/raw/master/bin/pyenv-installer | bash
   
   

   
   


3. 
   

   Add init lines to your ~/.profile or ~/.bashrc (it mentions it at the end of the install script):

   
   
   

   export PATH="~/.pyenv/bin:$PATH"
   
   eval "$(pyenv init -)"
   
   eval "$(pyenv virtualenv-init -)"
   
   

   
   



4. Restart your shell (close & open or exec $SHELL) or reload the profile script. (with e.g. source ~/.bashrc)

Done!

Setting up an environment

To not touch the system Python (generally a bad idea; OS-level services might be relying on some specific library versions, etc.) make your own environment, it's easy! Even better, no sudo, for it or pip installs!

1. 
   

   Install your preferred Python version (this will download the source and build it for your user, no input required)

   
   
   

   pyenv install 3.6.0
   
   

   
   


2. 
   

   Make it a virtualenv so you can make others later if you want

   
   
   

   pyenv virtualenv 3.6.0 general
   
   

   
   


3. 
   

   Make it globally active (for your user)

   
   
   

   pyenv global general
   
   

   
   



4. Do what you want to with the Python/pip, etc. It's yours.

If you want to clean out your libraries later, you could delete the virtualenv (pyenv uninstall general) or make a new one (pyenv virtualenv 3.6.0 other_proj). You can also have environments active per-directory: pyenv local other_proj will drop a .python-version file into your current folder and any time you invoke Python or pip-installed Python utilities from it or under it, they will be shimmed by pyenv.

Troubleshooting

• 
  

  bash: pyenv: command not found, fish: Unknown command 'pyenv'

  
  
  
  
  
  1. Check your $PATH, there should be one entry that ends in something like .pyenv/bin. If it's missing make sure you followed #3 AND #4 (restart your shell) under Install pyenv above.
  
  
  
  


• 
  

  pyenv: no such command 'virtualenv'

  
  
  
  
  
  1. If you didn't use the installer script, you likely only installed the root pyenv package. See pyenv-virtualenv for instructions to add the plugin
  
  
  2. If you used the installer script, check if it shows up with pyenv commands.