2. Using Python on Unix platforms
*********************************


2.1. Getting and installing the latest version of Python
========================================================


2.1.1. On Linux
---------------

Python comes preinstalled on most Linux distributions, and is
available as a package on all others.  However there are certain
features you might want to use that are not available on your distro's
package.  You can easily compile the latest version of Python from
source.

In the event that Python doesn't come preinstalled and isn't in the
repositories as well, you can easily make packages for your own
distro.  Have a look at the following links:

See also:

  https://www.debian.org/doc/manuals/maint-guide/first.en.html
     for Debian users

  https://en.opensuse.org/Portal:Packaging
     for OpenSuse users

  https://docs-old.fedoraproject.org/en-
  US/Fedora_Draft_Documentation/0.1/html/RPM_Guide/ch-creating-
  rpms.html
     for Fedora users

  http://www.slackbook.org/html/package-management-making-
  packages.html
     for Slackware users


2.1.2. On FreeBSD and OpenBSD
-----------------------------

* FreeBSD users, to add the package use:

     pkg install python3

* OpenBSD users, to add the package use:

     pkg_add -r python

     pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/4.2/packages/<insert your architecture here>/python-<version>.tgz

  For example i386 users get the 2.5.1 version of Python using:

     pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/4.2/packages/i386/python-2.5.1p2.tgz


2.1.3. On OpenSolaris
---------------------

You can get Python from OpenCSW.  Various versions of Python are
available and can be installed with e.g. "pkgutil -i python27".


2.2. Building Python
====================

If you want to compile CPython yourself, first thing you should do is
get the source. You can download either the latest release's source or
just grab a fresh clone.  (If you want to contribute patches, you will
need a clone.)

The build process consists of the usual commands:

   ./configure
   make
   make install

Configuration options and caveats for specific Unix platforms are
extensively documented in the README.rst file in the root of the
Python source tree.

Warning:

  "make install" can overwrite or masquerade the "python3" binary.
  "make altinstall" is therefore recommended instead of "make install"
  since it only installs "*exec_prefix*/bin/python*version*".


2.3. Python-related paths and files
===================================

These are subject to difference depending on local installation
conventions; "prefix" ("${prefix}") and "exec_prefix"
("${exec_prefix}") are installation-dependent and should be
interpreted as for GNU software; they may be the same.

For example, on most Linux systems, the default for both is "/usr".

+-------------------------------------------------+--------------------------------------------+
| File/directory                                  | Meaning                                    |
|=================================================|============================================|
| "*exec_prefix*/bin/python3"                     | Recommended location of the interpreter.   |
+-------------------------------------------------+--------------------------------------------+
| "*prefix*/lib/python*version*",                 | Recommended locations of the directories   |
| "*exec_prefix*/lib/python*version*"             | containing the standard modules.           |
+-------------------------------------------------+--------------------------------------------+
| "*prefix*/include/python*version*",             | Recommended locations of the directories   |
| "*exec_prefix*/include/python*version*"         | containing the include files needed for    |
|                                                 | developing Python extensions and embedding |
|                                                 | the interpreter.                           |
+-------------------------------------------------+--------------------------------------------+


2.4. Miscellaneous
==================

To easily use Python scripts on Unix, you need to make them
executable, e.g. with

   $ chmod +x script

and put an appropriate Shebang line at the top of the script.  A good
choice is usually

   #!/usr/bin/env python3

which searches for the Python interpreter in the whole "PATH".
However, some Unices may not have the **env** command, so you may need
to hardcode "/usr/bin/python3" as the interpreter path.

To use shell commands in your Python scripts, look at the "subprocess"
module.


2.5. Custom OpenSSL
===================

1. To use your vendor's OpenSSL configuration and system trust store,
   locate the directory with "openssl.cnf" file or symlink in "/etc".
   On most distribution the file is either in "/etc/ssl" or
   "/etc/pki/tls". The directory should also contain a "cert.pem" file
   and/or a "certs" directory.

      $ find /etc/ -name openssl.cnf -printf "%h\n"
      /etc/ssl

2. Download, build, and install OpenSSL. Make sure you use
   "install_sw" and not "install". The "install_sw" target does not
   override "openssl.cnf".

      $ curl -O https://www.openssl.org/source/openssl-VERSION.tar.gz
      $ tar xzf openssl-VERSION
      $ pushd openssl-VERSION
      $ ./config \
          --prefix=/usr/local/custom-openssl \
          --libdir=lib \
          --openssldir=/etc/ssl
      $ make -j1 depend
      $ make -j8
      $ make install_sw
      $ popd

3. Build Python with custom OpenSSL (see the configure "--with-
   openssl" and "--with-openssl-rpath" options)

      $ pushd python-3.x.x
      $ ./configure -C \
          --with-openssl=/usr/local/custom-openssl \
          --with-openssl-rpath=auto \
          --prefix=/usr/local/python-3.x.x
      $ make -j8
      $ make altinstall

Note:

  Patch releases of OpenSSL have a backwards compatible ABI. You don't
  need to recompile Python to update OpenSSL. It's sufficient to
  replace the custom OpenSSL installation with a newer version.
