Define %python, but make it work only if %__python is redefined

macros.python-srpm

@@ -15,6 +15,15 @@
 # See the comments in https://src.fedoraproject.org/rpms/python-rpm-macros/pull-request/22
 %__python /usr/bin/python
 
+# Users can use %%python only if they redefined %%__python (e.g. to %%__python3)
+%python() %{lua:\
+    __python = rpm.expand("%__python")\
+    if __python == "/usr/bin/python" then\
+        rpm.expand("%{error:Cannot use %%python if %%__python wasn't redefined to something other than /usr/bin/python.}")\
+    else\
+        print(__python)\
+    end\
+}
 
 # python3_pkgversion specifies the version of Python 3 in the distro.  It can be
 # a specific version (e.g. 34 in Fedora EPEL7)

python-rpm-macros.spec

@@ -1,6 +1,6 @@
 Name:           python-rpm-macros
 Version:        3
-Release:        50%{?dist}
+Release:        51%{?dist}
 Summary:        The unversioned Python RPM macros
 
 # macros: MIT, compileall2.py: PSFv2
@@ -78,6 +78,9 @@ install -m 644 %{SOURCE5} \
 
 
 %changelog
+* Sat Dec 28 2019 Miro Hrončok <mhroncok@redhat.com> - 3-51
+- Define %%python, but make it work only if %%__python is redefined
+
 * Tue Nov 26 2019 Lumír Balhar <lbalhar@redhat.com> - 3-50
 - Update of bundled compileall2 module