Index: Mk/Uses/python.mk
===================================================================
--- Mk/Uses/python.mk
+++ Mk/Uses/python.mk
@@ -247,6 +247,24 @@
 .endif
 
 # COMPAT KNOBS, remove them, once the tree is cleaned
+.undef _PY_COMPAT_OLD
+# We will reuse USE_PYTHON with a different meaning, so make sure that, while
+# we are in the transition phase from USE_PYTHON -> USES=python, it is mapped
+# and reassigned correctly
+.if defined(USE_PYTHON_BUILD) || defined(USE_PYTHON_RUN)
+# old style
+_PY_COMPAT_OLD= yes
+.elif defined(USE_PYTHON)
+.if ${USE_PYTHON} == "yes"
+# old style
+_PY_COMPAT_OLD= yes
+.elif ${USE_PYTHON:C/[-0-9.+]*//} == ""
+# old style X.Y, X.Y+, X.Y-, -X.Y, X.Y-Z.A
+_PY_COMPAT_OLD=	yes
+.endif # ${USE_PYTHON} == "yes" ...
+.endif # defined(USE_PYTHON_BUILD) || defined(USE_PYTHON_RUN)
+
+.if defined(_PY_COMPAT_OLD)
 .if defined(USE_PYTHON)
 .if ${USE_PYTHON} != "yes"
 python_ARGS=	${USE_PYTHON}
@@ -254,37 +272,47 @@
 .elif defined(USE_PYTHON_BUILD)
 .if ${USE_PYTHON_BUILD} != "yes"
 python_ARGS=	${USE_PYTHON_BUILD},build
+.else
+python_ARGS=	build
 .endif
 .elif defined(USE_PYTHON_RUN)
 .if ${USE_PYTHON_RUN} != "yes"
 python_ARGS=	${USE_PYTHON_RUN},run
+.else
+python_ARGS=	run
 .endif
 .endif # defined(USE_PYTHON)
-.if !defined(PYTHON_FEATURES)
-PYTHON_FEATURES=
+# Everything passed to python_ARGS, undef USE_PYTHON, since we will reuse
+# it with a different meaning below
+.undef USE_PYTHON
+.endif # defined(_PY_COMPAT_OLD)
+.undef _PY_COMPAT_OLD
+
+.if !defined(USE_PYTHON)
+USE_PYTHON=
 .if defined(USE_PYDISTUTILS)
-PYTHON_FEATURES+=	distutils
+USE_PYTHON+=	distutils
 .endif
 .if defined(PYDISTUTILS_AUTOPLIST)
-PYTHON_FEATURES+=	autoplist
+USE_PYTHON+=	autoplist
 .endif
 .if defined(PYTHON_PY3K_PLIST_HACK)
-PYTHON_FEATURES+=	py3kplist
+USE_PYTHON+=	py3kplist
 .endif
 .if defined(PYTHON_CONCURRENT_INSTALL)
-PYTHON_FEATURES+=	concurrent
+USE_PYTHON+=	concurrent
 .endif
 .if defined(USE_PYTHON_PREFIX)
-PYTHON_FEATURES+=	pythonprefix
+USE_PYTHON+=	pythonprefix
 .endif
 .if defined(PYDISTUTILS_NOEGGINFO)
-PYTHON_FEATURES+=	noegginfo
+USE_PYTHON+=	noegginfo
 .endif
-.endif # !defined(PYTHON_FEATURES)
+.endif # !defined(USE_PYTHON)
 # COMPAT KNOBS END
 
 # Make each individual feature available as _PYTHON_FEATURE_<FEATURENAME>
-.for var in ${PYTHON_FEATURES:S/,/ /g}
+.for var in ${USE_PYTHON:S/,/ /g}
 _PYTHON_FEATURE_${var:tu}=	yes
 .endfor
 
Index: Mk/bsd.sanity.mk
===================================================================
--- Mk/bsd.sanity.mk
+++ Mk/bsd.sanity.mk
@@ -119,10 +119,11 @@
 .endif
 
 .if defined(USE_PYTHON)
-.if ${USE_PYTHON} != "yes"
-DEV_WARNING+=	"USE_PYTHON is deprecated, please use USES=python:${USE_PYTHON}"
+_PYTHON_VAL := ${USE_PYTHON}
+.if ${_PYTHON_VAL} != "yes"
+DEV_WARNING+=	"USE_PYTHON=[version] is deprecated, please use USES=python:${_PYTHON_VAL}"
 .else
-DEV_WARNING+=	"USE_PYTHON is deprecated, please use USES=python"
+DEV_WARNING+=	"USE_PYTHON=yes is deprecated, please use USES=python"
 .endif
 .endif
 .if defined(USE_PYTHON_RUN)
@@ -172,12 +173,12 @@
 USE_GETTEXT_ALT=	USES=gettext
 USE_SCONS_ALT=		USES=scons
 USE_DRUPAL_ALT=		USES=drupal
-USE_PYDISTUTILS_ALT=		PYTHON_FEATURES=distutils
-PYTHON_CONCURRENT_INSTALL_ALT=	PYTHON_FEATURES=concurrent
-PYDISTUTILS_AUTOPLIST_ALT=	PYTHON_FEATURES=autoplist
-PYTHON_PY3K_PLIST_HACK_ALT=	PYTHON_FEATURES=py3kplist
-PYDISTUTILS_NOEGGINFO_ALT=	PYTHON_FEATURES=noegginfo
-USE_PYTHON_PREFIX_ALT=		PYTHON_FEATURES=pythonprefix
+USE_PYDISTUTILS_ALT=		USE_PYTHON=distutils
+PYTHON_CONCURRENT_INSTALL_ALT=	USE_PYTHON=concurrent
+PYDISTUTILS_AUTOPLIST_ALT=	USE_PYTHON=autoplist
+PYTHON_PY3K_PLIST_HACK_ALT=	USE_PYTHON=py3kplist
+PYDISTUTILS_NOEGGINFO_ALT=	USE_PYTHON=noegginfo
+USE_PYTHON_PREFIX_ALT=		USE_PYTHON=pythonprefix
 PYTHON_PKGNAMESUFFIX_ALT=	PYTHON_PKGNAMEPREFIX
 PYTHON_MASTER_SITES_ALT=	MASTER_SITE_PYTHON