dev-qt/qtpositioning: stable 5.14.2 for ppc, bug #719732
[gentoo.git] / eclass / python-single-r1.eclass
index 9e80866bfb516a7061b1c80488d7dac5f1ab0b68..d516e3629696b502a1b42fddc44697697e55f107 100644 (file)
@@ -1,6 +1,5 @@
-# Copyright 1999-2015 Gentoo Foundation
+# Copyright 1999-2020 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
-# $Id$
 
 # @ECLASS: python-single-r1.eclass
 # @MAINTAINER:
@@ -8,16 +7,22 @@
 # @AUTHOR:
 # Author: Michał Górny <mgorny@gentoo.org>
 # Based on work of: Krzysztof Pawlik <nelchael@gentoo.org>
+# @SUPPORTED_EAPIS: 5 6 7
 # @BLURB: An eclass for Python packages not installed for multiple implementations.
 # @DESCRIPTION:
 # An extension of the python-r1 eclass suite for packages which
 # don't support being installed for multiple Python implementations.
-# This mostly includes tools embedding Python.
+# This mostly includes tools embedding Python and packages using foreign
+# build systems.
 #
-# This eclass extends the IUSE and REQUIRED_USE set by python-r1
-# to request the PYTHON_SINGLE_TARGET when the inheriting ebuild
-# can be supported by more than one Python implementation. It also
-# replaces PYTHON_USEDEP and PYTHON_DEPS with a more suitable form.
+# This eclass sets correct IUSE.  It also provides PYTHON_DEPS
+# and PYTHON_REQUIRED_USE that need to be added to appropriate ebuild
+# metadata variables.
+#
+# The eclass exports PYTHON_SINGLE_USEDEP that is suitable for depending
+# on other packages using the eclass.  Dependencies on packages using
+# python-r1 should be created via python_gen_cond_dep() function,
+# using PYTHON_USEDEP placeholder.
 #
 # Please note that packages support multiple Python implementations
 # (using python-r1 eclass) can not depend on packages not supporting
 # in the packages using python-single-r1, and there is no need ever
 # to inherit both.
 #
-# For more information, please see the wiki:
-# https://wiki.gentoo.org/wiki/Project:Python/python-single-r1
+# For more information, please see the Python Guide:
+# https://dev.gentoo.org/~mgorny/python-guide/
 
 case "${EAPI:-0}" in
-       0|1|2|3)
+       0|1|2|3|4)
                die "Unsupported EAPI=${EAPI:-0} (too old) for ${ECLASS}"
                ;;
-       4)
-               # EAPI=4 is only allowed on legacy packages
-               if [[ ${CATEGORY}/${P} == app-arch/threadzip-1.2 ]]; then
-                       :
-               elif [[ ${CATEGORY}/${P} == media-libs/lv2-1.8.0 ]]; then
-                       :
-               elif [[ ${CATEGORY}/${P} == media-libs/lv2-1.10.0 ]]; then
-                       :
-               elif [[ ${CATEGORY}/${P} == sys-apps/paludis-1* ]]; then
-                       :
-               elif [[ ${CATEGORY}/${P} == sys-apps/paludis-2.[02].0 ]]; then
-                       :
-               elif [[ ${CATEGORY}/${P} == sys-apps/util-linux-2.2[456]* ]]; then
-                       :
-               elif [[ ${CATEGORY}/${P} == */gdb-7.[78]* ]]; then
-                       :
-               else
-                       die "Unsupported EAPI=${EAPI:-4} (too old, allowed only on restricted set of packages) for ${ECLASS}"
-               fi
-               ;;
-       5|6)
+       5|6|7)
                # EAPI=5 is required for sane USE_EXPAND dependencies
                ;;
        *)
@@ -77,8 +62,6 @@ fi
 
 EXPORT_FUNCTIONS pkg_setup
 
-if [[ ! ${_PYTHON_SINGLE_R1} ]]; then
-
 # @ECLASS-VARIABLE: PYTHON_COMPAT
 # @REQUIRED
 # @DESCRIPTION:
@@ -88,7 +71,7 @@ if [[ ! ${_PYTHON_SINGLE_R1} ]]; then
 #
 # Example:
 # @CODE
-# PYTHON_COMPAT=( python2_7 python3_3 python3_4} )
+# PYTHON_COMPAT=( python2_7 python3_3 python3_4 )
 # @CODE
 #
 # Please note that you can also use bash brace expansion if you like:
@@ -106,9 +89,9 @@ if [[ ! ${_PYTHON_SINGLE_R1} ]]; then
 #
 # It should be noted that in order to preserve metadata immutability,
 # PYTHON_COMPAT_OVERRIDE does not affect IUSE nor dependencies.
-# The state of PYTHON_TARGETS and PYTHON_SINGLE_TARGET is ignored,
-# and the implementation in PYTHON_COMPAT_OVERRIDE is built instead.
-# Dependencies need to be satisfied manually.
+# The state of PYTHON_SINGLE_TARGET is ignored, and the implementation
+# in PYTHON_COMPAT_OVERRIDE is built instead.  Dependencies need to be
+# satisfied manually.
 #
 # Example:
 # @CODE
@@ -153,35 +136,55 @@ if [[ ! ${_PYTHON_SINGLE_R1} ]]; then
 # @CODE
 # dev-lang/python-exec:=
 # python_single_target_python2_7? ( dev-lang/python:2.7[gdbm] )
-# python_single_target_pypy? ( virtual/pypy[gdbm] )
+# python_single_target_pypy? ( dev-python/pypy[gdbm] )
 # @CODE
 
-# @ECLASS-VARIABLE: PYTHON_USEDEP
+# @ECLASS-VARIABLE: PYTHON_SINGLE_USEDEP
 # @DESCRIPTION:
 # This is an eclass-generated USE-dependency string which can be used to
-# depend on another Python package being built for the same Python
-# implementations.
+# depend on another python-single-r1 package being built for the same
+# Python implementations.
+#
+# If you need to depend on a multi-impl (python-r1) package, use
+# python_gen_cond_dep with PYTHON_USEDEP placeholder instead.
+#
+# Example use:
+# @CODE
+# RDEPEND="dev-python/foo[${PYTHON_SINGLE_USEDEP}]"
+# @CODE
 #
-# The generate USE-flag list is compatible with packages using python-r1,
-# python-single-r1 and python-distutils-ng eclasses. It must not be used
-# on packages using python.eclass.
+# Example value:
+# @CODE
+# python_single_target_python3_4(-)?
+# @CODE
+
+# @ECLASS-VARIABLE: PYTHON_USEDEP
+# @DESCRIPTION:
+# This is a placeholder variable supported by python_gen_cond_dep,
+# in order to depend on python-r1 packages built for the same Python
+# implementations.
 #
 # Example use:
 # @CODE
-# RDEPEND="dev-python/foo[${PYTHON_USEDEP}]"
+# RDEPEND="$(python_gen_cond_dep '
+#     dev-python/foo[${PYTHON_USEDEP}]
+#   ')"
 # @CODE
 #
 # Example value:
 # @CODE
-# python_targets_python2_7(-)?,python_single_target_python3_4(+)?
+# python_targets_python3_4(-)
 # @CODE
 
+# @ECLASS-VARIABLE: PYTHON_MULTI_USEDEP
+# @DESCRIPTION:
+# This is a backwards-compatibility placeholder.  Use PYTHON_USEDEP
+# instead.
+
 # @ECLASS-VARIABLE: PYTHON_REQUIRED_USE
 # @DESCRIPTION:
-# This is an eclass-generated required-use expression which ensures the following
-# when more than one python implementation is possible:
-# 1. Exactly one PYTHON_SINGLE_TARGET value has been enabled.
-# 2. The selected PYTHON_SINGLE_TARGET value is enabled in PYTHON_TARGETS.
+# This is an eclass-generated required-use expression which ensures
+# that exactly one PYTHON_SINGLE_TARGET value has been enabled.
 #
 # This expression should be utilized in an ebuild by including it in
 # REQUIRED_USE, optionally behind a use flag.
@@ -193,114 +196,101 @@ if [[ ! ${_PYTHON_SINGLE_R1} ]]; then
 #
 # Example value:
 # @CODE
-# python_single_target_python2_7? ( python_targets_python2_7 )
-# python_single_target_python3_3? ( python_targets_python3_3 )
 # ^^ ( python_single_target_python2_7 python_single_target_python3_3 )
 # @CODE
 
 _python_single_set_globals() {
        _python_set_impls
 
-       PYTHON_DEPS=
-       local i PYTHON_PKG_DEP
-
-       local flags_mt=( "${_PYTHON_SUPPORTED_IMPLS[@]/#/python_targets_}" )
        local flags=( "${_PYTHON_SUPPORTED_IMPLS[@]/#/python_single_target_}" )
-       local unflags=( "${_PYTHON_UNSUPPORTED_IMPLS[@]/#/-python_single_target_}" )
-
-       local optflags=${flags_mt[@]/%/(-)?},${unflags[@]/%/(-)}
-
-       IUSE="${flags_mt[*]}"
 
        if [[ ${#_PYTHON_SUPPORTED_IMPLS[@]} -eq 1 ]]; then
-               # There is only one supported implementation; set IUSE and other
-               # variables without PYTHON_SINGLE_TARGET.
-               PYTHON_REQUIRED_USE="${flags_mt[*]}"
-               python_export "${_PYTHON_SUPPORTED_IMPLS[0]}" PYTHON_PKG_DEP
-               PYTHON_DEPS="${PYTHON_PKG_DEP} "
-               # Force on the python_single_target_* flag for this impl, so
-               # that any dependencies that inherit python-single-r1 and
-               # happen to have multiple implementations will still need
-               # to bound by the implementation used by this package.
-               optflags+=,${flags[0]/%/(+)}
+               # if only one implementation is supported, use IUSE defaults
+               # to avoid requesting the user to enable it
+               IUSE="+${flags[0]}"
        else
-               # Multiple supported implementations; honor PYTHON_SINGLE_TARGET.
-               IUSE+=" ${flags[*]}"
-               PYTHON_REQUIRED_USE="^^ ( ${flags[*]} )"
-               # Ensure deps honor the same python_single_target_* flag as is set
-               # on this package.
-               optflags+=,${flags[@]/%/(+)?}
-
-               for i in "${_PYTHON_SUPPORTED_IMPLS[@]}"; do
-                       # The chosen targets need to be in PYTHON_TARGETS as well.
-                       # This is in order to enforce correct dependencies on packages
-                       # supporting multiple implementations.
-                       PYTHON_REQUIRED_USE+=" python_single_target_${i}? ( python_targets_${i} )"
-
-                       python_export "${i}" PYTHON_PKG_DEP
-                       PYTHON_DEPS+="python_single_target_${i}? ( ${PYTHON_PKG_DEP} ) "
-               done
+               IUSE="${flags[*]}"
        fi
-       PYTHON_USEDEP=${optflags// /,}
-
-       # 1) well, python-exec would suffice as an RDEP
-       # but no point in making this overcomplex, BDEP doesn't hurt anyone
-       # 2) python-exec should be built with all targets forced anyway
-       # but if new targets were added, we may need to force a rebuild
-       # 3) use whichever python-exec slot installed in EAPI 5. For EAPI 4,
-       # just fix :2 since := deps are not supported.
-       if [[ ${_PYTHON_WANT_PYTHON_EXEC2} == 0 ]]; then
-               die "python-exec:0 is no longer supported, please fix your ebuild to work with python-exec:2"
-       elif [[ ${EAPI} != 4 ]]; then
-               PYTHON_DEPS+=">=dev-lang/python-exec-2:=[${PYTHON_USEDEP}]"
+
+       local requse="^^ ( ${flags[*]} )"
+       local single_flags="${flags[@]/%/(-)?}"
+       local single_usedep=${single_flags// /,}
+
+       local deps= i PYTHON_PKG_DEP
+       for i in "${_PYTHON_SUPPORTED_IMPLS[@]}"; do
+               _python_export "${i}" PYTHON_PKG_DEP
+               # 1) well, python-exec would suffice as an RDEP
+               # but no point in making this overcomplex, BDEP doesn't hurt anyone
+               # 2) python-exec should be built with all targets forced anyway
+               # but if new targets were added, we may need to force a rebuild
+               deps+="python_single_target_${i}? (
+                       ${PYTHON_PKG_DEP}
+                       >=dev-lang/python-exec-2:=[python_targets_${i}]
+               ) "
+       done
+
+       if [[ ${PYTHON_DEPS+1} ]]; then
+               if [[ ${PYTHON_DEPS} != "${deps}" ]]; then
+                       eerror "PYTHON_DEPS have changed between inherits (PYTHON_REQ_USE?)!"
+                       eerror "Before: ${PYTHON_DEPS}"
+                       eerror "Now   : ${deps}"
+                       die "PYTHON_DEPS integrity check failed"
+               fi
+
+               # these two are formality -- they depend on PYTHON_COMPAT only
+               if [[ ${PYTHON_REQUIRED_USE} != ${requse} ]]; then
+                       eerror "PYTHON_REQUIRED_USE have changed between inherits!"
+                       eerror "Before: ${PYTHON_REQUIRED_USE}"
+                       eerror "Now   : ${requse}"
+                       die "PYTHON_REQUIRED_USE integrity check failed"
+               fi
+
+               if [[ ${PYTHON_SINGLE_USEDEP} != "${single_usedep}" ]]; then
+                       eerror "PYTHON_SINGLE_USEDEP have changed between inherits!"
+                       eerror "Before: ${PYTHON_SINGLE_USEDEP}"
+                       eerror "Now   : ${single_usedep}"
+                       die "PYTHON_SINGLE_USEDEP integrity check failed"
+               fi
        else
-               PYTHON_DEPS+="dev-lang/python-exec:2[${PYTHON_USEDEP}]"
+               PYTHON_DEPS=${deps}
+               PYTHON_REQUIRED_USE=${requse}
+               PYTHON_USEDEP='%PYTHON_USEDEP-NEEDS-TO-BE-USED-IN-PYTHON_GEN_COND_DEP%'
+               PYTHON_SINGLE_USEDEP=${single_usedep}
+               readonly PYTHON_DEPS PYTHON_REQUIRED_USE PYTHON_SINGLE_USEDEP \
+                       PYTHON_USEDEP
        fi
-       readonly PYTHON_DEPS PYTHON_REQUIRED_USE PYTHON_USEDEP
 }
 _python_single_set_globals
 unset -f _python_single_set_globals
 
-# @FUNCTION: python_gen_usedep
-# @USAGE: <pattern> [...]
+if [[ ! ${_PYTHON_SINGLE_R1} ]]; then
+
+# @FUNCTION: _python_gen_usedep
+# @INTERNAL
+# @USAGE: [<pattern>...]
 # @DESCRIPTION:
 # Output a USE dependency string for Python implementations which
 # are both in PYTHON_COMPAT and match any of the patterns passed
 # as parameters to the function.
 #
-# Remember to escape or quote the patterns to prevent shell filename
-# expansion.
-#
-# When all implementations are requested, please use ${PYTHON_USEDEP}
-# instead. Please also remember to set an appropriate REQUIRED_USE
-# to avoid ineffective USE flags.
-#
-# Example:
-# @CODE
-# PYTHON_COMPAT=( python{2_7,3_4} )
-# DEPEND="doc? ( dev-python/epydoc[$(python_gen_usedep 'python2*')] )"
-# @CODE
+# The patterns can be either fnmatch-style patterns (matched via bash
+# == operator against PYTHON_COMPAT values) or '-2' / '-3' to indicate
+# appropriately all enabled Python 2/3 implementations (alike
+# python_is_python3). Remember to escape or quote the fnmatch patterns
+# to prevent accidental shell filename expansion.
 #
-# It will cause the dependency to look like:
-# @CODE
-# DEPEND="doc? ( dev-python/epydoc[python_targets_python2_7(-)?,...] )"
-# @CODE
-python_gen_usedep() {
+# This is an internal function used to implement python_gen_cond_dep.
+_python_gen_usedep() {
        debug-print-function ${FUNCNAME} "${@}"
 
-       local impl pattern
-       local matches=()
+       local impl matches=()
 
        for impl in "${_PYTHON_SUPPORTED_IMPLS[@]}"; do
-               for pattern; do
-                       if [[ ${impl} == ${pattern} ]]; then
-                               matches+=(
-                                       "python_targets_${impl}(-)?"
-                                       "python_single_target_${impl}(+)?"
-                               )
-                               break
-                       fi
-               done
+               if _python_impl_matches "${impl}" "${@}"; then
+                       matches+=(
+                               "python_single_target_${impl}(-)?"
+                       )
+               fi
        done
 
        [[ ${matches[@]} ]] || die "No supported implementations match python_gen_usedep patterns: ${@}"
@@ -310,12 +300,18 @@ python_gen_usedep() {
 }
 
 # @FUNCTION: python_gen_useflags
-# @USAGE: <pattern> [...]
+# @USAGE: [<pattern>...]
 # @DESCRIPTION:
 # Output a list of USE flags for Python implementations which
 # are both in PYTHON_COMPAT and match any of the patterns passed
 # as parameters to the function.
 #
+# The patterns can be either fnmatch-style patterns (matched via bash
+# == operator against PYTHON_COMPAT values) or '-2' / '-3' to indicate
+# appropriately all enabled Python 2/3 implementations (alike
+# python_is_python3). Remember to escape or quote the fnmatch patterns
+# to prevent accidental shell filename expansion.
+#
 # Example:
 # @CODE
 # PYTHON_COMPAT=( python{2_7,3_4} )
@@ -329,38 +325,34 @@ python_gen_usedep() {
 python_gen_useflags() {
        debug-print-function ${FUNCNAME} "${@}"
 
-       local flag_prefix impl pattern
-       local matches=()
-
-       if [[ ${#_PYTHON_SUPPORTED_IMPLS[@]} -eq 1 ]]; then
-               flag_prefix=python_targets
-       else
-               flag_prefix=python_single_target
-       fi
+       local impl matches=()
 
        for impl in "${_PYTHON_SUPPORTED_IMPLS[@]}"; do
-               for pattern; do
-                       if [[ ${impl} == ${pattern} ]]; then
-                               matches+=( "${flag_prefix}_${impl}" )
-                               break
-                       fi
-               done
+               if _python_impl_matches "${impl}" "${@}"; then
+                       matches+=( "python_single_target_${impl}" )
+               fi
        done
 
        echo "${matches[@]}"
 }
 
 # @FUNCTION: python_gen_cond_dep
-# @USAGE: <dependency> <pattern> [...]
+# @USAGE: <dependency> [<pattern>...]
 # @DESCRIPTION:
 # Output a list of <dependency>-ies made conditional to USE flags
 # of Python implementations which are both in PYTHON_COMPAT and match
 # any of the patterns passed as the remaining parameters.
 #
+# The patterns can be either fnmatch-style patterns (matched via bash
+# == operator against PYTHON_COMPAT values) or '-2' / '-3' to indicate
+# appropriately all enabled Python 2/3 implementations (alike
+# python_is_python3). Remember to escape or quote the fnmatch patterns
+# to prevent accidental shell filename expansion.
+#
 # In order to enforce USE constraints on the packages, verbatim
-# '${PYTHON_USEDEP}' (quoted!) may be placed in the dependency
-# specification. It will get expanded within the function into a proper
-# USE dependency string.
+# '${PYTHON_SINGLE_USEDEP}' and '${PYTHON_USEDEP}' (quoted!) may
+# be placed in the dependency specification. It will get expanded within
+# the function into a proper USE dependency string.
 #
 # Example:
 # @CODE
@@ -379,33 +371,26 @@ python_gen_useflags() {
 python_gen_cond_dep() {
        debug-print-function ${FUNCNAME} "${@}"
 
-       local flag_prefix impl pattern
-       local matches=()
-
-       if [[ ${#_PYTHON_SUPPORTED_IMPLS[@]} -eq 1 ]]; then
-               flag_prefix=python_targets
-       else
-               flag_prefix=python_single_target
-       fi
+       local impl matches=()
 
        local dep=${1}
        shift
 
        for impl in "${_PYTHON_SUPPORTED_IMPLS[@]}"; do
-               for pattern; do
-                       if [[ ${impl} == ${pattern} ]]; then
-                               # substitute ${PYTHON_USEDEP} if used
-                               # (since python_gen_usedep() will not return ${PYTHON_USEDEP}
-                               #  the code is run at most once)
-                               if [[ ${dep} == *'${PYTHON_USEDEP}'* ]]; then
-                                       local usedep=$(python_gen_usedep "${@}")
-                                       dep=${dep//\$\{PYTHON_USEDEP\}/${usedep}}
-                               fi
-
-                               matches+=( "${flag_prefix}_${impl}? ( ${dep} )" )
-                               break
+               if _python_impl_matches "${impl}" "${@}"; then
+                       # substitute ${PYTHON_SINGLE_USEDEP} if used
+                       # (since python_gen_usedep() will not return
+                       #  ${PYTHON_SINGLE_USEDEP}, the code is run at most once)
+                       if [[ ${dep} == *'${PYTHON_SINGLE_USEDEP}'* ]]; then
+                               local usedep=$(_python_gen_usedep "${@}")
+                               dep=${dep//\$\{PYTHON_SINGLE_USEDEP\}/${usedep}}
                        fi
-               done
+                       local multi_usedep="python_targets_${impl}(-)"
+
+                       local subdep=${dep//\$\{PYTHON_MULTI_USEDEP\}/${multi_usedep}}
+                       matches+=( "python_single_target_${impl}? (
+                               ${subdep//\$\{PYTHON_USEDEP\}/${multi_usedep}} )" )
+               fi
        done
 
        echo "${matches[@]}"
@@ -420,6 +405,12 @@ python_gen_cond_dep() {
 # patterns are passed, the output dependencies will be generated only
 # for the implementations matching them.
 #
+# The patterns can be either fnmatch-style patterns (matched via bash
+# == operator against PYTHON_COMPAT values) or '-2' / '-3' to indicate
+# appropriately all enabled Python 2/3 implementations (alike
+# python_is_python3). Remember to escape or quote the fnmatch patterns
+# to prevent accidental shell filename expansion.
+#
 # Use this function when you need to request different USE flags
 # on the Python interpreter depending on package's USE flags. If you
 # only need a single set of interpreter USE flags, just set
@@ -442,28 +433,18 @@ python_gen_cond_dep() {
 python_gen_impl_dep() {
        debug-print-function ${FUNCNAME} "${@}"
 
-       local impl pattern
+       local impl
        local matches=()
 
-       if [[ ${#_PYTHON_SUPPORTED_IMPLS[@]} -eq 1 ]]; then
-               flag_prefix=python_targets
-       else
-               flag_prefix=python_single_target
-       fi
-
        local PYTHON_REQ_USE=${1}
        shift
 
-       local patterns=( "${@-*}" )
        for impl in "${_PYTHON_SUPPORTED_IMPLS[@]}"; do
-               for pattern in "${patterns[@]}"; do
-                       if [[ ${impl} == ${pattern} ]]; then
-                               local PYTHON_PKG_DEP
-                               python_export "${impl}" PYTHON_PKG_DEP
-                               matches+=( "${flag_prefix}_${impl}? ( ${PYTHON_PKG_DEP} )" )
-                               break
-                       fi
-               done
+               if _python_impl_matches "${impl}" "${@}"; then
+                       local PYTHON_PKG_DEP
+                       _python_export "${impl}" PYTHON_PKG_DEP
+                       matches+=( "python_single_target_${impl}? ( ${PYTHON_PKG_DEP} )" )
+               fi
        done
 
        echo "${matches[@]}"
@@ -490,57 +471,38 @@ python_setup() {
                ewarn
                ewarn "Dependencies won't be satisfied, and PYTHON_SINGLE_TARGET flags will be ignored."
 
-               python_export "${impls[0]}" EPYTHON PYTHON
-               python_wrapper_setup
+               _python_export "${impls[0]}" EPYTHON PYTHON
+               _python_wrapper_setup
+               einfo "Using ${EPYTHON} to build"
                return
        fi
 
-       if [[ ${#_PYTHON_SUPPORTED_IMPLS[@]} -eq 1 ]]; then
-               if use "python_targets_${_PYTHON_SUPPORTED_IMPLS[0]}"; then
-                       # Only one supported implementation, enable it explicitly
-                       python_export "${_PYTHON_SUPPORTED_IMPLS[0]}" EPYTHON PYTHON
-                       python_wrapper_setup
-               fi
-       else
-               local impl
-               for impl in "${_PYTHON_SUPPORTED_IMPLS[@]}"; do
-                       if use "python_single_target_${impl}"; then
-                               if [[ ${EPYTHON} ]]; then
-                                       eerror "Your PYTHON_SINGLE_TARGET setting lists more than a single Python"
-                                       eerror "implementation. Please set it to just one value. If you need"
-                                       eerror "to override the value for a single package, please use package.env"
-                                       eerror "or an equivalent solution (man 5 portage)."
-                                       echo
-                                       die "More than one implementation in PYTHON_SINGLE_TARGET."
-                               fi
-
-                               if ! use "python_targets_${impl}"; then
-                                       eerror "The implementation chosen as PYTHON_SINGLE_TARGET must be added"
-                                       eerror "to PYTHON_TARGETS as well. This is in order to ensure that"
-                                       eerror "dependencies are satisfied correctly. We're sorry"
-                                       eerror "for the inconvenience."
-                                       echo
-                                       die "Build target (${impl}) not in PYTHON_TARGETS."
-                               fi
-
-                               python_export "${impl}" EPYTHON PYTHON
-                               python_wrapper_setup
+       local impl
+       for impl in "${_PYTHON_SUPPORTED_IMPLS[@]}"; do
+               if use "python_single_target_${impl}"; then
+                       if [[ ${EPYTHON} ]]; then
+                               eerror "Your PYTHON_SINGLE_TARGET setting lists more than a single Python"
+                               eerror "implementation. Please set it to just one value. If you need"
+                               eerror "to override the value for a single package, please use package.env"
+                               eerror "or an equivalent solution (man 5 portage)."
+                               echo
+                               die "More than one implementation in PYTHON_SINGLE_TARGET."
                        fi
-               done
-       fi
+
+                       _python_export "${impl}" EPYTHON PYTHON
+                       _python_wrapper_setup
+                       einfo "Using ${EPYTHON} to build"
+               fi
+       done
 
        if [[ ! ${EPYTHON} ]]; then
                eerror "No Python implementation selected for the build. Please set"
-               if [[ ${#_PYTHON_SUPPORTED_IMPLS[@]} -eq 1 ]]; then
-                       eerror "the PYTHON_TARGETS variable in your make.conf to include one"
-               else
-                       eerror "the PYTHON_SINGLE_TARGET variable in your make.conf to one"
-               fi
+               eerror "the PYTHON_SINGLE_TARGET variable in your make.conf to one"
                eerror "of the following values:"
                eerror
                eerror "${_PYTHON_SUPPORTED_IMPLS[@]}"
                echo
-               die "No supported Python implementation in PYTHON_SINGLE_TARGET/PYTHON_TARGETS."
+               die "No supported Python implementation in PYTHON_SINGLE_TARGET."
        fi
 }