only build docs for default python3

not for all supported python3 versions.

Closes: #942794.

debian/changelog

 python-scipy (1.2.2-8) UNRELEASED; urgency=medium
 
+  [ Ondřej Nový ]
   * Bump Standards-Version to 4.4.1.
 
+  [ Drew Parsons ]
+  * only build docs for default python3. Closes: #942794.
+
  -- Ondřej Nový <onovy@debian.org>  Fri, 18 Oct 2019 15:55:02 +0200
 
 python-scipy (1.2.2-7) unstable; urgency=medium

debian/rules

@@ -11,6 +11,7 @@ export PATH := $(CURDIR)/debian/extra_bin:$(PATH)
 
 PY2VERS:= $(shell pyversions -v -r debian/control)
 PY3VERS:= $(shell py3versions -v -r debian/control)
+PY3_DEFAULT:= $(shell py3versions -d)
 TMPDIR := $(CURDIR)/build/tmp
 BASE=$(shell pwd)/debian
 
@@ -44,7 +45,7 @@ override_dh_auto_build-arch: $(PY2VERS:%=build-python%) $(PY3VERS:%=build-python
 override_dh_auto_build-indep: $(PY3VERS:%=build-python%)
 	# generate documentation (see comment below) needs compiled scipy
 	(export MPLCONFIGDIR=. ; \
-	PYLIBPATH=`pybuild --print build_dir | awk '{print $$3}'`; \
+	PYLIBPATH=`pybuild --print build_dir | grep $(PY3_DEFAULT) | awk '{print $$3}'`; \
 	echo "building docs using PYLIBPATH=$$PYLIBPATH"; \
 	make -C doc html PYTHONPATH=$$PYLIBPATH PYVER=3)