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10.5 Python

Automake provides support for Python compilation with the PYTHON primary. A typical setup is to call AM_PATH_PYTHON in configure.ac and use a line like the following in Makefile.am: 

     python_PYTHON = tree.py leave.py

Any files listed in a _PYTHON variable will be byte-compiled with py-compile at install time. py-compile actually creates both standard (.pyc) and optimized (.pyo) byte-compiled versions of the source files. Note that because byte-compilation occurs at install time, any files listed in noinst_PYTHON will not be compiled. Python source files are included in the distribution by default, prepend nodist_ (as in nodist_python_PYTHON) to omit them.

Automake ships with an Autoconf macro called AM_PATH_PYTHON that will determine some Python-related directory variables (see below). If you have called AM_PATH_PYTHON from configure.ac, then you may use the variables python_PYTHON or pkgpython_PYTHON to list Python source files in your Makefile.am, depending where you want your files installed (see the definitions of pythondir and pkgpythondir below).

— Macro: AM_PATH_PYTHON ([VERSION], [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])

Search for a Python interpreter on the system. This macro takes three optional arguments. The first argument, if present, is the minimum version of Python required for this package: AM_PATH_PYTHON will skip any Python interpreter that is older than VERSION. If an interpreter is found and satisfies VERSION, then ACTION-IF-FOUND is run. Otherwise, ACTION-IF-NOT-FOUND is run.

If ACTION-IF-NOT-FOUND is not specified, as in the following example, the default is to abort configure. 

          AM_PATH_PYTHON([2.2])

This is fine when Python is an absolute requirement for the package. If Python >= 2.2 was only optional to the package, AM_PATH_PYTHON could be called as follows. 

          AM_PATH_PYTHON([2.2],, [:])

AM_PATH_PYTHON creates the following output variables based on the Python installation found during configuration.

PYTHON
The name of the Python executable, or ‘:’ if no suitable interpreter could be found.

Assuming ACTION-IF-NOT-FOUND is used (otherwise ./configure will abort if Python is absent), the value of PYTHON can be used to setup a conditional in order to disable the relevant part of a build as follows. 

            AM_PATH_PYTHON(,, [:])
            AM_CONDITIONAL([HAVE_PYTHON], [test "$PYTHON" != :])

PYTHON_VERSION
The Python version number, in the form major.minor (e.g., ‘1.5’). This is currently the value of ‘sys.version[:3]’.
PYTHON_PREFIX
The string ‘${prefix}’. This term may be used in future work that needs the contents of Python's ‘sys.prefix’, but general consensus is to always use the value from configure.
PYTHON_EXEC_PREFIX
The string ‘${exec_prefix}’. This term may be used in future work that needs the contents of Python's ‘sys.exec_prefix’, but general consensus is to always use the value from configure.
PYTHON_PLATFORM
The canonical name used by Python to describe the operating system, as given by ‘sys.platform’. This value is sometimes needed when building Python extensions.
pythondir
The directory name for the site-packages subdirectory of the standard Python install tree.
pkgpythondir
This is the directory under pythondir that is named after the package. That is, it is ‘$(pythondir)/$(PACKAGE)’. It is provided as a convenience.
pyexecdir
This is the directory where Python extension modules (shared libraries) should be installed. An extension module written in C could be declared as follows to Automake: 
          pyexec_LTLIBRARIES = quaternion.la
          quaternion_SOURCES = quaternion.c support.c support.h
          quaternion_la_LDFLAGS = -avoid-version -module

pkgpyexecdir
This is a convenience variable that is defined as ‘$(pyexecdir)/$(PACKAGE)’.

All these directory variables have values that start with either ‘${prefix}’ or ‘${exec_prefix}’ unexpanded. This works fine in Makefiles, but it makes these variables hard to use in configure. This is mandated by the GNU coding standards, so that the user can run ‘make prefix=/foo install’. The Autoconf manual has a section with more details on this topic (see Installation Directory Variables). See also Hard-Coded Install Paths.