use %{__python3} as the python interpreter

units.spec

@@ -1,7 +1,7 @@
 Summary: A utility for converting amounts from one unit to another
 Name: units
 Version: 2.17
-Release: 2%{?dist}
+Release: 3%{?dist}
 Source: https://ftp.gnu.org/gnu/units/%{name}-%{version}.tar.gz
 URL: https://www.gnu.org/software/units/units.html
 License: GPLv3+
@@ -11,7 +11,7 @@ BuildRequires: automake
 BuildRequires: bison
 BuildRequires: gcc
 BuildRequires: ncurses-devel
-BuildRequires: python3
+BuildRequires: python3-devel
 BuildRequires: readline-devel
 
 %description
@@ -24,7 +24,8 @@ well as conversions such as Fahrenheit to Celsius.
 %autosetup -p1
 
 # make units_cur use Python 3
-sed -e 's|^AC_PATH_PROG(PYTHON, python|&3|' -i configure.ac
+sed -e 's|^AC_PATH_PROG(PYTHON, .*$|PYTHON=%{__python3}\nAC_SUBST(PYTHON)|' \
+    -i configure.ac
 autoreconf -fiv
 
 %build
@@ -62,6 +63,9 @@ fi
 %{_mandir}/man1/*
 
 %changelog
+* Wed Jul 04 2018 Kamil Dudka <kdudka@redhat.com> - 2.17-3
+- use %%{__python3} as the python interpreter
+
 * Wed Jun 27 2018 Kamil Dudka <kdudka@redhat.com> - 2.17-2
 - drop the dependency on python3-unidecode no longer used by units_cur