Add operator and quotes to the AX_PYTHON_DEVEL parameter The operator is required and the quotes are needed to protect PYTHON_VERSION. See-also: https://www.gnu.org/software/autoconf-archive/ax_python_devel.html Fixes: checking whether to build the libpst python interface... yes checking for python build information... checking for python3.7... python3.7 checking for main in -lpython3.7... no checking for main in -lpython3.7m... yes results of the Python check: Binary: python3.7 Library: python3.7m Include Dir: /usr/include/python3.7m checking for python3.7... /usr/bin/python3.7 checking for a version of Python >= '2.1.0'... yes checking for a version of Python 3.7... File "<string>", line 1 import sys; ver = sys.version.split ()[0]; print (ver 3.7) ^ SyntaxError: invalid syntax no configure: error: this package requires Python 3.7. If you have it installed, but it isn't the default Python interpreter in your system path, please pass the PYTHON_VERSION variable to configure. See ``configure --help'' for reference.

if PYTHON_INTERFACE

if PLATFORM_WIN32
    NO_UNDEFINED = -no-undefined
else
    NO_UNDEFINED =
endif

pythonlibdir            = $(libdir)/@PYTHON_VERSION@/site-packages
pythonlib_LTLIBRARIES   = _libpst.la
_libpst_la_LDFLAGS      = -module $(NO_UNDEFINED) -avoid-version
_libpst_la_SOURCES      = python-libpst.cpp
_libpst_la_LIBADD       = -l@BOOST_PYTHON_LIB@ ../src/libpst.la

# set the include path found by configure
INCLUDES= -I$(srcdir)/.. -I$(srcdir)/../src $(all_includes) -I$(PYTHON_INCLUDE_DIR)

endif