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:

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/pythonversion.

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/pythonversion`, `exec_prefix/lib/pythonversion`	Recommended locations of the directories containing the standard modules.
`prefix/include/pythonversion`, `exec_prefix/include/pythonversion`	Recommended locations of the directories 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¶

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
```

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 \
        --openssldir=/etc/ssl
   $ make -j1 depend
   $ make -j8
   $ make install_sw
   $ popd

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.