Supported python build in host side.

The base module handles all the common functionalites, such as version
compatibilty check, version variations split, source file format check,
source/data file duplicate check.

The library/binary module focuses on how to generate binary build actions,
such as setting up stub script, zipping, filling in __init__.py in
runfiles dir tree.

Bug: b/31676493
Test: go test under python package

Change-Id: I06608369f350f7195873d459e1c8d1bdb811e77e

10 files changed, 1494 insertions, 16 deletions

diff --git a/Android.bp b/Android.bp
index 61ef41e3..e2fb8648 100644
--- a/Android.bp
+++ b/Android.bp
@@ -209,6 +209,25 @@ bootstrap_go_package {
     pluginFor: ["soong_build"],
 }
 
+bootstrap_go_package {
+    name: "soong-python",
+    pkgPath: "android/soong/python",
+    deps: [
+        "blueprint",
+        "soong-android",
+    ],
+    srcs: [
+        "python/binary.go",
+        "python/builder.go",
+        "python/library.go",
+        "python/python.go",
+    ],
+    testSrcs: [
+        "python/python_test.go",
+    ],
+    pluginFor: ["soong_build"],
+}
+
 //
 // Defaults to enable various configurations of host bionic
 //
diff --git a/android/androidmk.go b/android/androidmk.go
index af6608f8..b81cc2a6 100644
--- a/android/androidmk.go
+++ b/android/androidmk.go
@@ -217,13 +217,22 @@ func translateAndroidMkModule(ctx blueprint.SingletonContext, w io.Writer, mod b
 	host := false
 	switch amod.Os().Class {
 	case Host:
-		fmt.Fprintln(w, "LOCAL_MODULE_HOST_ARCH :=", archStr)
+		// Make cannot identify LOCAL_MODULE_HOST_ARCH:= common.
+		if archStr != "common" {
+			fmt.Fprintln(w, "LOCAL_MODULE_HOST_ARCH :=", archStr)
+		}
 		host = true
 	case HostCross:
-		fmt.Fprintln(w, "LOCAL_MODULE_HOST_CROSS_ARCH :=", archStr)
+		// Make cannot identify LOCAL_MODULE_HOST_CROSS_ARCH:= common.
+		if archStr != "common" {
+			fmt.Fprintln(w, "LOCAL_MODULE_HOST_CROSS_ARCH :=", archStr)
+		}
 		host = true
 	case Device:
-		fmt.Fprintln(w, "LOCAL_MODULE_TARGET_ARCH :=", archStr)
+		// Make cannot identify LOCAL_MODULE_TARGET_ARCH:= common.
+		if archStr != "common" {
+			fmt.Fprintln(w, "LOCAL_MODULE_TARGET_ARCH :=", archStr)
+		}
 
 		if len(amod.commonProperties.Logtags) > 0 {
 			fmt.Fprintln(w, "LOCAL_LOGTAGS_FILES := ", strings.Join(amod.commonProperties.Logtags, " "))
diff --git a/android/arch.go b/android/arch.go
index e21a0705..39477ad7 100644
--- a/android/arch.go
+++ b/android/arch.go
@@ -189,7 +189,8 @@ var BuildOs = func() OsType {
 }()
 
 var (
-	osTypeList []OsType
+	osTypeList      []OsType
+	commonTargetMap = make(map[string]Target)
 
 	NoOsType    OsType
 	Linux       = NewOsType("linux", Host, false)
@@ -236,6 +237,13 @@ func NewOsType(name string, class OsClass, defDisabled bool) OsType {
 		DefaultDisabled: defDisabled,
 	}
 	osTypeList = append(osTypeList, os)
+
+	if _, found := commonTargetMap[name]; found {
+		panic(fmt.Errorf("Found Os type duplicate during OsType registration: %q", name))
+	} else {
+		commonTargetMap[name] = Target{Os: os, Arch: Arch{ArchType: Common}}
+	}
+
 	return os
 }
 
@@ -249,15 +257,6 @@ func osByName(name string) OsType {
 	return NoOsType
 }
 
-var (
-	commonTarget = Target{
-		Os: Android,
-		Arch: Arch{
-			ArchType: Common,
-		},
-	}
-)
-
 type Target struct {
 	Os   OsType
 	Arch Arch
@@ -989,6 +988,20 @@ func filterMultilibTargets(targets []Target, multilib string) []Target {
 	return ret
 }
 
+func getCommonTargets(targets []Target) []Target {
+	var ret []Target
+	set := make(map[string]bool)
+
+	for _, t := range targets {
+		if _, found := set[t.Os.String()]; !found {
+			set[t.Os.String()] = true
+			ret = append(ret, commonTargetMap[t.Os.String()])
+		}
+	}
+
+	return ret
+}
+
 // Use the module multilib setting to select one or more targets from a target list
 func decodeMultilib(multilib string, targets []Target, prefer32 bool) ([]Target, error) {
 	buildTargets := []Target{}
@@ -1001,7 +1014,7 @@ func decodeMultilib(multilib string, targets []Target, prefer32 bool) ([]Target,
 	}
 	switch multilib {
 	case "common":
-		buildTargets = append(buildTargets, commonTarget)
+		buildTargets = append(buildTargets, getCommonTargets(targets)...)
 	case "both":
 		if prefer32 {
 			buildTargets = append(buildTargets, filterMultilibTargets(targets, "lib32")...)
diff --git a/android/mutator.go b/android/mutator.go
index 940b0ffb..bb494878 100644
--- a/android/mutator.go
+++ b/android/mutator.go
@@ -81,8 +81,18 @@ func registerMutators(ctx *blueprint.Context) {
 }
 
 func RegisterTestMutators(ctx *blueprint.Context) {
-	mutators := registerMutatorsContext{}
+	mutators := &registerMutatorsContext{}
+
+	register := func(funcs []RegisterMutatorFunc) {
+		for _, f := range funcs {
+			f(mutators)
+		}
+	}
+
+	register(testPreDeps)
 	mutators.BottomUp("deps", depsMutator).Parallel()
+	register(testPostDeps)
+
 	registerMutatorsToContext(ctx, mutators.mutators)
 }
 
@@ -97,7 +107,7 @@ type RegisterMutatorsContext interface {
 
 type RegisterMutatorFunc func(RegisterMutatorsContext)
 
-var preArch, preDeps, postDeps []RegisterMutatorFunc
+var preArch, preDeps, postDeps, testPreDeps, testPostDeps []RegisterMutatorFunc
 
 func PreArchMutators(f RegisterMutatorFunc) {
 	preArch = append(preArch, f)
@@ -111,6 +121,14 @@ func PostDepsMutators(f RegisterMutatorFunc) {
 	postDeps = append(postDeps, f)
 }
 
+func TestPreDepsMutators(f RegisterMutatorFunc) {
+	testPreDeps = append(testPreDeps, f)
+}
+
+func TeststPostDepsMutators(f RegisterMutatorFunc) {
+	testPostDeps = append(testPostDeps, f)
+}
+
 type AndroidTopDownMutator func(TopDownMutatorContext)
 
 type TopDownMutatorContext interface {
diff --git a/python/binary.go b/python/binary.go
new file mode 100644
index 00000000..4b4ccc28
--- /dev/null
+++ b/python/binary.go
@@ -0,0 +1,235 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package python
+
+// This file contains the module types for building Python binary.
+
+import (
+	"fmt"
+	"io"
+	"path/filepath"
+	"strings"
+
+	"github.com/google/blueprint"
+
+	"android/soong/android"
+)
+
+func init() {
+	android.RegisterModuleType("python_binary_host", PythonBinaryHostFactory)
+}
+
+type PythonBinaryProperties struct {
+	// the name of the source file that is the main entry point of the program.
+	// this file must also be listed in srcs.
+	// If left unspecified, module name is used instead.
+	// If name doesn’t match any filename in srcs, main must be specified.
+	Main string
+
+	// set the name of the output binary.
+	Stem string
+
+	// append to the name of the output binary.
+	Suffix string
+}
+
+type PythonBinary struct {
+	pythonBaseModule
+
+	binaryProperties PythonBinaryProperties
+
+	// soong_zip arguments from all its dependencies.
+	depsParSpecs []parSpec
+
+	// Python runfiles paths from all its dependencies.
+	depsPyRunfiles []string
+
+	// the installation path for Python binary.
+	installPath android.OutputPath
+}
+
+var _ PythonSubModule = (*PythonBinary)(nil)
+
+var (
+	stubTemplateHost = "build/soong/python/scripts/stub_template_host.txt"
+)
+
+func PythonBinaryHostFactory() (blueprint.Module, []interface{}) {
+	module := &PythonBinary{}
+
+	return InitPythonBaseModule(&module.pythonBaseModule, module, android.HostSupportedNoCross,
+		&module.binaryProperties)
+}
+
+func (p *PythonBinary) GeneratePythonBuildActions(ctx android.ModuleContext) {
+	p.pythonBaseModule.GeneratePythonBuildActions(ctx)
+
+	// no Python source file for compiling par file.
+	if len(p.pythonBaseModule.srcsPathMappings) == 0 && len(p.depsPyRunfiles) == 0 {
+		return
+	}
+
+	// the runfiles packages needs to be populated with "__init__.py".
+	newPyPkgs := []string{}
+	// the set to de-duplicate the new Python packages above.
+	newPyPkgSet := make(map[string]bool)
+	// the runfiles dirs have been treated as packages.
+	existingPyPkgSet := make(map[string]bool)
+
+	wholePyRunfiles := []string{}
+	for _, path := range p.pythonBaseModule.srcsPathMappings {
+		wholePyRunfiles = append(wholePyRunfiles, path.dest)
+	}
+	wholePyRunfiles = append(wholePyRunfiles, p.depsPyRunfiles...)
+
+	// find all the runfiles dirs which have been treated as packages.
+	for _, path := range wholePyRunfiles {
+		if filepath.Base(path) != initFileName {
+			continue
+		}
+		existingPyPkg := PathBeforeLastSlash(path)
+		if _, found := existingPyPkgSet[existingPyPkg]; found {
+			panic(fmt.Errorf("found init file path duplicates: %q for module: %q.",
+				path, ctx.ModuleName()))
+		} else {
+			existingPyPkgSet[existingPyPkg] = true
+		}
+		parentPath := PathBeforeLastSlash(existingPyPkg)
+		populateNewPyPkgs(parentPath, existingPyPkgSet, newPyPkgSet, &newPyPkgs)
+	}
+
+	// create new packages under runfiles tree.
+	for _, path := range wholePyRunfiles {
+		if filepath.Base(path) == initFileName {
+			continue
+		}
+		parentPath := PathBeforeLastSlash(path)
+		populateNewPyPkgs(parentPath, existingPyPkgSet, newPyPkgSet, &newPyPkgs)
+	}
+
+	main := p.getPyMainFile(ctx)
+	if main == "" {
+		return
+	}
+	interp := p.getInterpreter(ctx)
+	if interp == "" {
+		return
+	}
+
+	// we need remove "runfiles/" suffix since stub script starts
+	// searching for main file in each sub-dir of "runfiles" directory tree.
+	binFile := registerBuildActionForParFile(ctx, p.getInterpreter(ctx),
+		strings.TrimPrefix(main, runFiles+"/"), p.getStem(ctx),
+		newPyPkgs, append(p.depsParSpecs, p.pythonBaseModule.parSpec))
+
+	// install par file.
+	p.installPath = ctx.InstallFile(
+		android.PathForModuleInstall(ctx, "bin"), binFile)
+}
+
+// get interpreter path.
+func (p *PythonBinary) getInterpreter(ctx android.ModuleContext) string {
+	var interp string
+	switch p.pythonBaseModule.properties.ActualVersion {
+	case pyVersion2:
+		interp = "python2"
+	case pyVersion3:
+		interp = "python3"
+	default:
+		panic(fmt.Errorf("unknown Python actualVersion: %q for module: %q.",
+			p.properties.ActualVersion, ctx.ModuleName()))
+	}
+
+	return interp
+}
+
+// find main program path within runfiles tree.
+func (p *PythonBinary) getPyMainFile(ctx android.ModuleContext) string {
+	var main string
+	if p.binaryProperties.Main == "" {
+		main = p.BaseModuleName() + pyExt
+	} else {
+		main = p.binaryProperties.Main
+	}
+
+	for _, path := range p.pythonBaseModule.srcsPathMappings {
+		if main == path.src.Rel() {
+			return path.dest
+		}
+	}
+	ctx.PropertyErrorf("main", "%q is not listed in srcs.", main)
+
+	return ""
+}
+
+func (p *PythonBinary) getStem(ctx android.ModuleContext) string {
+	stem := ctx.ModuleName()
+	if p.binaryProperties.Stem != "" {
+		stem = p.binaryProperties.Stem
+	}
+
+	return stem + p.binaryProperties.Suffix
+}
+
+// Sets the given directory and all its ancestor directories as Python packages.
+func populateNewPyPkgs(pkgPath string, existingPyPkgSet,
+	newPyPkgSet map[string]bool, newPyPkgs *[]string) {
+	for pkgPath != "" {
+		if _, found := existingPyPkgSet[pkgPath]; found {
+			break
+		}
+		if _, found := newPyPkgSet[pkgPath]; !found {
+			newPyPkgSet[pkgPath] = true
+			*newPyPkgs = append(*newPyPkgs, pkgPath)
+			// Gets its ancestor directory by trimming last slash.
+			pkgPath = PathBeforeLastSlash(pkgPath)
+		} else {
+			break
+		}
+	}
+}
+
+// filepath.Dir("abc") -> "." and filepath.Dir("/abc") -> "/". However,
+// the PathBeforeLastSlash() will return "" for both cases above.
+func PathBeforeLastSlash(path string) string {
+	if idx := strings.LastIndex(path, "/"); idx != -1 {
+		return path[:idx]
+	}
+	return ""
+}
+
+func (p *PythonBinary) GeneratePythonAndroidMk() (ret android.AndroidMkData, err error) {
+	// Soong installation is only supported for host modules. Have Make
+	// installation trigger Soong installation.
+	if p.pythonBaseModule.Target().Os.Class == android.Host {
+		ret.OutputFile = android.OptionalPathForPath(p.installPath)
+	}
+	ret.Class = "EXECUTABLES"
+
+	ret.Extra = append(ret.Extra, func(w io.Writer, outputFile android.Path) error {
+		path := p.installPath.RelPathString()
+		dir, file := filepath.Split(path)
+		stem := strings.TrimSuffix(file, filepath.Ext(file))
+
+		fmt.Fprintln(w, "LOCAL_MODULE_SUFFIX := "+filepath.Ext(file))
+		fmt.Fprintln(w, "LOCAL_MODULE_PATH := $(OUT_DIR)/"+filepath.Clean(dir))
+		fmt.Fprintln(w, "LOCAL_MODULE_STEM := "+stem)
+
+		return nil
+	})
+
+	return
+
+}
diff --git a/python/builder.go b/python/builder.go
new file mode 100644
index 00000000..62234486
--- /dev/null
+++ b/python/builder.go
@@ -0,0 +1,146 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package python
+
+// This file contains Ninja build actions for building Python program.
+
+import (
+	"strings"
+
+	"android/soong/android"
+
+	"github.com/google/blueprint"
+	_ "github.com/google/blueprint/bootstrap"
+)
+
+var (
+	pctx = android.NewPackageContext("android/soong/python")
+
+	par = pctx.AndroidStaticRule("par",
+		blueprint.RuleParams{
+			Command: `touch $initFile && ` +
+				`sed -e 's/%interpreter%/$interp/g' -e 's/%main%/$main/g' $template > $stub && ` +
+				`$parCmd -o $parFile $parArgs && echo '#!/usr/bin/env python' | cat - $parFile > $out && ` +
+				`chmod +x $out && (rm -f $initFile; rm -f $stub; rm -f $parFile)`,
+			CommandDeps: []string{"$parCmd", "$template"},
+			Description: "build par $out",
+		},
+		"initFile", "interp", "main", "template", "stub", "parCmd", "parFile", "parArgs")
+)
+
+func init() {
+	pctx.Import("github.com/google/blueprint/bootstrap")
+	pctx.Import("android/soong/common")
+
+	pctx.HostBinToolVariable("parCmd", "soong_zip")
+}
+
+type fileListSpec struct {
+	fileList     android.Path
+	relativeRoot string
+}
+
+type parSpec struct {
+	rootPrefix string
+
+	fileListSpecs []fileListSpec
+}
+
+func (p parSpec) soongParArgs() string {
+	ret := "-P " + p.rootPrefix
+
+	for _, spec := range p.fileListSpecs {
+		ret += " -C " + spec.relativeRoot + " -l " + spec.fileList.String()
+	}
+
+	return ret
+}
+
+func registerBuildActionForModuleFileList(ctx android.ModuleContext,
+	name string, files android.Paths) android.Path {
+	fileList := android.PathForModuleOut(ctx, name+".list")
+
+	content := []string{}
+	for _, file := range files {
+		content = append(content, file.String())
+	}
+
+	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
+		Rule:      android.WriteFile,
+		Output:    fileList,
+		Implicits: files,
+		Args: map[string]string{
+			"content": strings.Join(content, "\n"),
+		},
+	})
+
+	return fileList
+}
+
+func registerBuildActionForParFile(ctx android.ModuleContext,
+	interpreter, main, binName string, newPyPkgs []string, parSpecs []parSpec) android.Path {
+
+	// intermediate output path for __init__.py
+	initFile := android.PathForModuleOut(ctx, initFileName).String()
+
+	// the path of stub_template_host.txt from source tree.
+	template := android.PathForSource(ctx, stubTemplateHost)
+
+	// intermediate output path for __main__.py
+	stub := android.PathForModuleOut(ctx, mainFileName).String()
+
+	// intermediate output path for par file.
+	parFile := android.PathForModuleOut(ctx, binName+parFileExt)
+
+	// intermediate output path for bin executable.
+	binFile := android.PathForModuleOut(ctx, binName)
+
+	// implicit dependency for parFile build action.
+	implicits := android.Paths{}
+	for _, p := range parSpecs {
+		for _, f := range p.fileListSpecs {
+			implicits = append(implicits, f.fileList)
+		}
+	}
+
+	parArgs := []string{}
+	parArgs = append(parArgs, "-C "+strings.TrimSuffix(stub, mainFileName)+" -f "+stub)
+	parArgs = append(parArgs, "-C "+strings.TrimSuffix(initFile, initFileName)+" -f "+initFile)
+	for _, pkg := range newPyPkgs {
+		parArgs = append(parArgs, "-P "+pkg+" -f "+initFile)
+	}
+	for _, p := range parSpecs {
+		parArgs = append(parArgs, p.soongParArgs())
+	}
+
+	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
+		Rule:      par,
+		Output:    binFile,
+		Implicits: implicits,
+		Args: map[string]string{
+			"initFile": initFile,
+			// the "\" isn't being interpreted by regex parser, it's being
+			// interpreted in the string literal.
+			"interp":   strings.Replace(interpreter, "/", `\/`, -1),
+			"main":     strings.Replace(main, "/", `\/`, -1),
+			"template": template.String(),
+			"stub":     stub,
+			"parFile":  parFile.String(),
+			"parArgs":  strings.Join(parArgs, " "),
+		},
+	})
+
+	return binFile
+}
diff --git a/python/library.go b/python/library.go
new file mode 100644
index 00000000..1deaeb8f
--- /dev/null
+++ b/python/library.go
@@ -0,0 +1,43 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package python
+
+// This file contains the module types for building Python library.
+
+import (
+	"github.com/google/blueprint"
+
+	"android/soong/android"
+)
+
+func init() {
+	android.RegisterModuleType("python_library_host", PythonLibraryHostFactory)
+}
+
+type PythonLibrary struct {
+	pythonBaseModule
+}
+
+var _ PythonSubModule = (*PythonLibrary)(nil)
+
+func PythonLibraryHostFactory() (blueprint.Module, []interface{}) {
+	module := &PythonLibrary{}
+
+	return InitPythonBaseModule(&module.pythonBaseModule, module, android.HostSupportedNoCross)
+}
+
+func (p *PythonLibrary) GeneratePythonAndroidMk() (ret android.AndroidMkData, err error) {
+	return
+}
diff --git a/python/python.go b/python/python.go
new file mode 100644
index 00000000..1c74c9af
--- /dev/null
+++ b/python/python.go
@@ -0,0 +1,448 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package python
+
+// This file contains the "Base" module type for building Python program.
+
+import (
+	"fmt"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strings"
+
+	"github.com/google/blueprint"
+
+	"android/soong/android"
+)
+
+func init() {
+	android.PreDepsMutators(func(ctx android.RegisterMutatorsContext) {
+		ctx.BottomUp("version_split", versionSplitMutator()).Parallel()
+	})
+}
+
+// the version properties that apply to python libraries and binaries.
+type PythonVersionProperties struct {
+	// true, if the module is required to be built with this version.
+	Enabled *bool
+
+	// if specified, common src files are converted to specific version with converter tool.
+	// Converter bool
+
+	// non-empty list of .py files under this strict Python version.
+	// srcs may reference the outputs of other modules that produce source files like genrule
+	// or filegroup using the syntax ":module".
+	Srcs []string
+
+	// list of the Python libraries under this Python version.
+	Libs []string
+}
+
+// properties that apply to python libraries and binaries.
+type PythonBaseModuleProperties struct {
+	// the package path prefix within the output artifact at which to place the source/data
+	// files of the current module.
+	// eg. Pkg_path = "a/b/c"; Other packages can reference this module by using
+	// (from a.b.c import ...) statement.
+	// if left unspecified, all the source/data files of current module are copied to
+	// "runfiles/" tree directory directly.
+	Pkg_path string
+
+	// list of source (.py) files compatible both with Python2 and Python3 used to compile the
+	// Python module.
+	// srcs may reference the outputs of other modules that produce source files like genrule
+	// or filegroup using the syntax ":module".
+	// Srcs has to be non-empty.
+	Srcs []string
+
+	// list of files or filegroup modules that provide data that should be installed alongside
+	// the test. the file extension can be arbitrary except for (.py).
+	Data []string
+
+	// list of the Python libraries compatible both with Python2 and Python3.
+	Libs []string
+
+	Version struct {
+		// all the "srcs" or Python dependencies that are to be used only for Python2.
+		Py2 PythonVersionProperties
+
+		// all the "srcs" or Python dependencies that are to be used only for Python3.
+		Py3 PythonVersionProperties
+	}
+
+	// the actual version each module uses after variations created.
+	// this property name is hidden from users' perspectives, and soong will populate it during
+	// runtime.
+	ActualVersion string `blueprint:"mutated"`
+}
+
+type pathMapping struct {
+	dest string
+	src  android.Path
+}
+
+type pythonBaseModule struct {
+	android.ModuleBase
+	subModule PythonSubModule
+
+	properties PythonBaseModuleProperties
+
+	// the Python files of current module after expanding source dependencies.
+	// pathMapping: <dest: runfile_path, src: source_path>
+	srcsPathMappings []pathMapping
+
+	// the data files of current module after expanding source dependencies.
+	// pathMapping: <dest: runfile_path, src: source_path>
+	dataPathMappings []pathMapping
+
+	// the soong_zip arguments for zipping current module source/data files.
+	parSpec parSpec
+}
+
+type PythonSubModule interface {
+	GeneratePythonBuildActions(ctx android.ModuleContext)
+	GeneratePythonAndroidMk() (ret android.AndroidMkData, err error)
+}
+
+type PythonDependency interface {
+	GetSrcsPathMappings() []pathMapping
+	GetDataPathMappings() []pathMapping
+	GetParSpec() parSpec
+}
+
+func (p *pythonBaseModule) GetSrcsPathMappings() []pathMapping {
+	return p.srcsPathMappings
+}
+
+func (p *pythonBaseModule) GetDataPathMappings() []pathMapping {
+	return p.dataPathMappings
+}
+
+func (p *pythonBaseModule) GetParSpec() parSpec {
+	return p.parSpec
+}
+
+var _ PythonDependency = (*pythonBaseModule)(nil)
+
+var _ android.AndroidMkDataProvider = (*pythonBaseModule)(nil)
+
+func InitPythonBaseModule(baseModule *pythonBaseModule, subModule PythonSubModule,
+	hod android.HostOrDeviceSupported,
+	props ...interface{}) (blueprint.Module, []interface{}) {
+
+	baseModule.subModule = subModule
+
+	props = append(props, &baseModule.properties)
+
+	return android.InitAndroidArchModule(baseModule, hod, android.MultilibCommon, props...)
+}
+
+// the tag used to mark dependencies within "py_libs" attribute.
+type pythonDependencyTag struct {
+	blueprint.BaseDependencyTag
+}
+
+var pyDependencyTag pythonDependencyTag
+
+var (
+	pyIdentifierRegexp = regexp.MustCompile(`^([a-z]|[A-Z]|_)([a-z]|[A-Z]|[0-9]|_)*$`)
+	pyExt              = ".py"
+	pyVersion2         = "PY2"
+	pyVersion3         = "PY3"
+	initFileName       = "__init__.py"
+	mainFileName       = "__main__.py"
+	parFileExt         = ".zip"
+	runFiles           = "runfiles"
+)
+
+// create version variants for modules.
+func versionSplitMutator() func(android.BottomUpMutatorContext) {
+	return func(mctx android.BottomUpMutatorContext) {
+		if base, ok := mctx.Module().(*pythonBaseModule); ok {
+			versionNames := []string{}
+			if base.properties.Version.Py2.Enabled != nil &&
+				*(base.properties.Version.Py2.Enabled) == true {
+				versionNames = append(versionNames, pyVersion2)
+			}
+			if !(base.properties.Version.Py3.Enabled != nil &&
+				*(base.properties.Version.Py3.Enabled) == false) {
+				versionNames = append(versionNames, pyVersion3)
+			}
+			modules := mctx.CreateVariations(versionNames...)
+			for i, v := range versionNames {
+				// set the actual version for Python module.
+				modules[i].(*pythonBaseModule).properties.ActualVersion = v
+			}
+		}
+	}
+}
+
+func (p *pythonBaseModule) DepsMutator(ctx android.BottomUpMutatorContext) {
+	// deps from "data".
+	android.ExtractSourcesDeps(ctx, p.properties.Data)
+	// deps from "srcs".
+	android.ExtractSourcesDeps(ctx, p.properties.Srcs)
+
+	switch p.properties.ActualVersion {
+	case pyVersion2:
+		// deps from "version.py2.srcs" property.
+		android.ExtractSourcesDeps(ctx, p.properties.Version.Py2.Srcs)
+
+		ctx.AddVariationDependencies(nil, pyDependencyTag,
+			uniqueLibs(ctx, p.properties.Libs, "version.py2.libs",
+				p.properties.Version.Py2.Libs)...)
+	case pyVersion3:
+		// deps from "version.py3.srcs" property.
+		android.ExtractSourcesDeps(ctx, p.properties.Version.Py3.Srcs)
+
+		ctx.AddVariationDependencies(nil, pyDependencyTag,
+			uniqueLibs(ctx, p.properties.Libs, "version.py3.libs",
+				p.properties.Version.Py3.Libs)...)
+	default:
+		panic(fmt.Errorf("unknown Python actualVersion: %q for module: %q.",
+			p.properties.ActualVersion, ctx.ModuleName()))
+	}
+}
+
+// check "libs" duplicates from current module dependencies.
+func uniqueLibs(ctx android.BottomUpMutatorContext,
+	commonLibs []string, versionProp string, versionLibs []string) []string {
+	set := make(map[string]string)
+	ret := []string{}
+
+	// deps from "libs" property.
+	for _, l := range commonLibs {
+		if _, found := set[l]; found {
+			ctx.PropertyErrorf("libs", "%q has duplicates within libs.", l)
+		} else {
+			set[l] = "libs"
+			ret = append(ret, l)
+		}
+	}
+	// deps from "version.pyX.libs" property.
+	for _, l := range versionLibs {
+		if _, found := set[l]; found {
+			ctx.PropertyErrorf(versionProp, "%q has duplicates within %q.", set[l])
+		} else {
+			set[l] = versionProp
+			ret = append(ret, l)
+		}
+	}
+
+	return ret
+}
+
+func (p *pythonBaseModule) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	p.subModule.GeneratePythonBuildActions(ctx)
+}
+
+func (p *pythonBaseModule) GeneratePythonBuildActions(ctx android.ModuleContext) {
+	// expand python files from "srcs" property.
+	srcs := p.properties.Srcs
+	switch p.properties.ActualVersion {
+	case pyVersion2:
+		srcs = append(srcs, p.properties.Version.Py2.Srcs...)
+	case pyVersion3:
+		srcs = append(srcs, p.properties.Version.Py3.Srcs...)
+	default:
+		panic(fmt.Errorf("unknown Python actualVersion: %q for module: %q.",
+			p.properties.ActualVersion, ctx.ModuleName()))
+	}
+	expandedSrcs := ctx.ExpandSources(srcs, nil)
+	if len(expandedSrcs) == 0 {
+		ctx.ModuleErrorf("doesn't have any source files!")
+	}
+
+	// expand data files from "data" property.
+	expandedData := ctx.ExpandSources(p.properties.Data, nil)
+
+	// sanitize pkg_path.
+	pkg_path := p.properties.Pkg_path
+	if pkg_path != "" {
+		pkg_path = filepath.Clean(p.properties.Pkg_path)
+		if pkg_path == ".." || strings.HasPrefix(pkg_path, "../") ||
+			strings.HasPrefix(pkg_path, "/") {
+			ctx.PropertyErrorf("pkg_path", "%q is not a valid format.",
+				p.properties.Pkg_path)
+			return
+		}
+		// pkg_path starts from "runfiles/" implicitly.
+		pkg_path = filepath.Join(runFiles, pkg_path)
+	} else {
+		// pkg_path starts from "runfiles/" implicitly.
+		pkg_path = runFiles
+	}
+
+	p.genModulePathMappings(ctx, pkg_path, expandedSrcs, expandedData)
+
+	p.parSpec = p.dumpFileList(ctx, pkg_path)
+
+	p.uniqWholeRunfilesTree(ctx)
+}
+
+// generate current module unique pathMappings: <dest: runfiles_path, src: source_path>
+// for python/data files.
+func (p *pythonBaseModule) genModulePathMappings(ctx android.ModuleContext, pkg_path string,
+	expandedSrcs, expandedData android.Paths) {
+	// fetch <runfiles_path, source_path> pairs from "src" and "data" properties to
+	// check duplicates.
+	destToPySrcs := make(map[string]string)
+	destToPyData := make(map[string]string)
+
+	for _, s := range expandedSrcs {
+		if s.Ext() != pyExt {
+			ctx.PropertyErrorf("srcs", "found non (.py) file: %q!", s.String())
+			continue
+		}
+		runfilesPath := filepath.Join(pkg_path, s.Rel())
+		identifiers := strings.Split(strings.TrimSuffix(runfilesPath, pyExt), "/")
+		for _, token := range identifiers {
+			if !pyIdentifierRegexp.MatchString(token) {
+				ctx.PropertyErrorf("srcs", "the path %q contains invalid token %q.",
+					runfilesPath, token)
+			}
+		}
+		if fillInMap(ctx, destToPySrcs, runfilesPath, s.String(), p.Name(), p.Name()) {
+			p.srcsPathMappings = append(p.srcsPathMappings,
+				pathMapping{dest: runfilesPath, src: s})
+		}
+	}
+
+	for _, d := range expandedData {
+		if d.Ext() == pyExt {
+			ctx.PropertyErrorf("data", "found (.py) file: %q!", d.String())
+			continue
+		}
+		runfilesPath := filepath.Join(pkg_path, d.Rel())
+		if fillInMap(ctx, destToPyData, runfilesPath, d.String(), p.Name(), p.Name()) {
+			p.dataPathMappings = append(p.dataPathMappings,
+				pathMapping{dest: runfilesPath, src: d})
+		}
+	}
+
+}
+
+// register build actions to dump filelist to disk.
+func (p *pythonBaseModule) dumpFileList(ctx android.ModuleContext, pkg_path string) parSpec {
+	relativeRootMap := make(map[string]android.Paths)
+	// the soong_zip params in order to pack current module's Python/data files.
+	ret := parSpec{rootPrefix: pkg_path}
+
+	pathMappings := append(p.srcsPathMappings, p.dataPathMappings...)
+
+	// "srcs" or "data" properties may have filegroup so it might happen that
+	// the relative root for each source path is different.
+	for _, path := range pathMappings {
+		relativeRoot := strings.TrimSuffix(path.src.String(), path.src.Rel())
+		if v, found := relativeRootMap[relativeRoot]; found {
+			relativeRootMap[relativeRoot] = append(v, path.src)
+		} else {
+			relativeRootMap[relativeRoot] = android.Paths{path.src}
+		}
+	}
+
+	var keys []string
+
+	// in order to keep stable order of soong_zip params, we sort the keys here.
+	for k := range relativeRootMap {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
+	for _, k := range keys {
+		// use relative root as filelist name.
+		fileListPath := registerBuildActionForModuleFileList(
+			ctx, strings.Replace(k, "/", "_", -1), relativeRootMap[k])
+		ret.fileListSpecs = append(ret.fileListSpecs,
+			fileListSpec{fileList: fileListPath, relativeRoot: k})
+	}
+
+	return ret
+}
+
+// check Python/data files duplicates from current module and its whole dependencies.
+func (p *pythonBaseModule) uniqWholeRunfilesTree(ctx android.ModuleContext) {
+	// fetch <runfiles_path, source_path> pairs from "src" and "data" properties to
+	// check duplicates.
+	destToPySrcs := make(map[string]string)
+	destToPyData := make(map[string]string)
+
+	for _, path := range p.srcsPathMappings {
+		destToPySrcs[path.dest] = path.src.String()
+	}
+	for _, path := range p.dataPathMappings {
+		destToPyData[path.dest] = path.src.String()
+	}
+
+	// visit all its dependencies in depth first.
+	ctx.VisitDepsDepthFirst(func(module blueprint.Module) {
+		// module can only depend on Python library.
+		if base, ok := module.(*pythonBaseModule); ok {
+			if _, ok := base.subModule.(*PythonLibrary); !ok {
+				panic(fmt.Errorf(
+					"the dependency %q of module %q is not Python library!",
+					ctx.ModuleName(), ctx.OtherModuleName(module)))
+			}
+		} else {
+			return
+		}
+		if dep, ok := module.(PythonDependency); ok {
+			srcs := dep.GetSrcsPathMappings()
+			for _, path := range srcs {
+				if !fillInMap(ctx, destToPySrcs,
+					path.dest, path.src.String(), ctx.ModuleName(),
+					ctx.OtherModuleName(module)) {
+					continue
+				}
+				// binary needs the Python runfiles paths from all its
+				// dependencies to fill __init__.py in each runfiles dir.
+				if sub, ok := p.subModule.(*PythonBinary); ok {
+					sub.depsPyRunfiles = append(sub.depsPyRunfiles, path.dest)
+				}
+			}
+			data := dep.GetDataPathMappings()
+			for _, path := range data {
+				fillInMap(ctx, destToPyData,
+					path.dest, path.src.String(), ctx.ModuleName(),
+					ctx.OtherModuleName(module))
+			}
+			// binary needs the soong_zip arguments from all its
+			// dependencies to generate executable par file.
+			if sub, ok := p.subModule.(*PythonBinary); ok {
+				sub.depsParSpecs = append(sub.depsParSpecs, dep.GetParSpec())
+			}
+		}
+	})
+}
+
+func fillInMap(ctx android.ModuleContext, m map[string]string,
+	key, value, curModule, otherModule string) bool {
+	if oldValue, found := m[key]; found {
+		ctx.ModuleErrorf("found two files to be placed at the same runfiles location %q."+
+			" First file: in module %s at path %q."+
+			" Second file: in module %s at path %q.",
+			key, curModule, oldValue, otherModule, value)
+		return false
+	} else {
+		m[key] = value
+	}
+
+	return true
+}
+
+func (p *pythonBaseModule) AndroidMk() (ret android.AndroidMkData, err error) {
+	return p.subModule.GeneratePythonAndroidMk()
+}
diff --git a/python/python_test.go b/python/python_test.go
new file mode 100644
index 00000000..c6b84519
--- /dev/null
+++ b/python/python_test.go
@@ -0,0 +1,456 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package python
+
+import (
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"reflect"
+	"sort"
+	"strings"
+	"testing"
+
+	"android/soong/android"
+
+	"github.com/google/blueprint"
+)
+
+type pyBinary struct {
+	name           string
+	actualVersion  string
+	pyRunfiles     []string
+	depsPyRunfiles []string
+	parSpec        string
+	depsParSpecs   []string
+}
+
+var (
+	buildNamePrefix          = "soong_python_test"
+	moduleVariantErrTemplate = "%s: module %q variant %q: "
+	pkgPathErrTemplate       = moduleVariantErrTemplate +
+		"pkg_path: %q is not a valid format."
+	badIdentifierErrTemplate = moduleVariantErrTemplate +
+		"srcs: the path %q contains invalid token %q."
+	dupRunfileErrTemplate = moduleVariantErrTemplate +
+		"found two files to be placed at the same runfiles location %q." +
+		" First file: in module %s at path %q." +
+		" Second file: in module %s at path %q."
+	noSrcFileErr      = moduleVariantErrTemplate + "doesn't have any source files!"
+	badSrcFileExtErr  = moduleVariantErrTemplate + "srcs: found non (.py) file: %q!"
+	badDataFileExtErr = moduleVariantErrTemplate + "data: found (.py) file: %q!"
+	bpFile            = "Blueprints"
+
+	data = []struct {
+		desc      string
+		mockFiles map[string][]byte
+
+		errors           []string
+		expectedBinaries []pyBinary
+	}{
+		{
+			desc: "module without any src files",
+			mockFiles: map[string][]byte{
+				bpFile: []byte(`subdirs = ["dir"]`),
+				filepath.Join("dir", bpFile): []byte(
+					`python_library_host {
+						name: "lib1",
+					}`,
+				),
+			},
+			errors: []string{
+				fmt.Sprintf(noSrcFileErr,
+					"dir/Blueprints:1:1", "lib1", "PY3"),
+			},
+		},
+		{
+			desc: "module with bad src file ext",
+			mockFiles: map[string][]byte{
+				bpFile: []byte(`subdirs = ["dir"]`),
+				filepath.Join("dir", bpFile): []byte(
+					`python_library_host {
+						name: "lib1",
+						srcs: [
+							"file1.exe",
+						],
+					}`,
+				),
+				"dir/file1.exe": nil,
+			},
+			errors: []string{
+				fmt.Sprintf(badSrcFileExtErr,
+					"dir/Blueprints:3:11", "lib1", "PY3", "dir/file1.exe"),
+			},
+		},
+		{
+			desc: "module with bad data file ext",
+			mockFiles: map[string][]byte{
+				bpFile: []byte(`subdirs = ["dir"]`),
+				filepath.Join("dir", bpFile): []byte(
+					`python_library_host {
+						name: "lib1",
+						srcs: [
+							"file1.py",
+						],
+						data: [
+							"file2.py",
+						],
+					}`,
+				),
+				"dir/file1.py": nil,
+				"dir/file2.py": nil,
+			},
+			errors: []string{
+				fmt.Sprintf(badDataFileExtErr,
+					"dir/Blueprints:6:11", "lib1", "PY3", "dir/file2.py"),
+			},
+		},
+		{
+			desc: "module with bad pkg_path format",
+			mockFiles: map[string][]byte{
+				bpFile: []byte(`subdirs = ["dir"]`),
+				filepath.Join("dir", bpFile): []byte(
+					`python_library_host {
+						name: "lib1",
+						pkg_path: "a/c/../../",
+						srcs: [
+							"file1.py",
+						],
+					}
+
+					python_library_host {
+						name: "lib2",
+						pkg_path: "a/c/../../../",
+						srcs: [
+							"file1.py",
+						],
+					}
+
+					python_library_host {
+						name: "lib3",
+						pkg_path: "/a/c/../../",
+						srcs: [
+							"file1.py",
+						],
+					}`,
+				),
+				"dir/file1.py": nil,
+			},
+			errors: []string{
+				fmt.Sprintf(pkgPathErrTemplate,
+					"dir/Blueprints:11:15", "lib2", "PY3", "a/c/../../../"),
+				fmt.Sprintf(pkgPathErrTemplate,
+					"dir/Blueprints:19:15", "lib3", "PY3", "/a/c/../../"),
+			},
+		},
+		{
+			desc: "module with bad runfile src path format",
+			mockFiles: map[string][]byte{
+				bpFile: []byte(`subdirs = ["dir"]`),
+				filepath.Join("dir", bpFile): []byte(
+					`python_library_host {
+						name: "lib1",
+						pkg_path: "a/b/c/",
+						srcs: [
+							".file1.py",
+							"123/file1.py",
+							"-e/f/file1.py",
+						],
+					}`,
+				),
+				"dir/.file1.py":     nil,
+				"dir/123/file1.py":  nil,
+				"dir/-e/f/file1.py": nil,
+			},
+			errors: []string{
+				fmt.Sprintf(badIdentifierErrTemplate, "dir/Blueprints:4:11",
+					"lib1", "PY3", "runfiles/a/b/c/-e/f/file1.py", "-e"),
+				fmt.Sprintf(badIdentifierErrTemplate, "dir/Blueprints:4:11",
+					"lib1", "PY3", "runfiles/a/b/c/.file1.py", ".file1"),
+				fmt.Sprintf(badIdentifierErrTemplate, "dir/Blueprints:4:11",
+					"lib1", "PY3", "runfiles/a/b/c/123/file1.py", "123"),
+			},
+		},
+		{
+			desc: "module with duplicate runfile path",
+			mockFiles: map[string][]byte{
+				bpFile: []byte(`subdirs = ["dir"]`),
+				filepath.Join("dir", bpFile): []byte(
+					`python_library_host {
+						name: "lib1",
+						pkg_path: "a/b/",
+						srcs: [
+							"c/file1.py",
+						],
+					}
+
+					python_library_host {
+						name: "lib2",
+						pkg_path: "a/b/c/",
+						srcs: [
+							"file1.py",
+						],
+						libs: [
+							"lib1",
+						],
+					}
+					`,
+				),
+				"dir/c/file1.py": nil,
+				"dir/file1.py":   nil,
+			},
+			errors: []string{
+				fmt.Sprintf(dupRunfileErrTemplate, "dir/Blueprints:9:6",
+					"lib2", "PY3", "runfiles/a/b/c/file1.py", "lib2", "dir/file1.py",
+					"lib1", "dir/c/file1.py"),
+			},
+		},
+		{
+			desc: "module for testing dependencies",
+			mockFiles: map[string][]byte{
+				bpFile: []byte(`subdirs = ["dir"]`),
+				filepath.Join("dir", bpFile): []byte(
+					`python_library_host {
+						name: "lib5",
+						pkg_path: "a/b/",
+						srcs: [
+							"file1.py",
+						],
+						version: {
+							py2: {
+								enabled: true,
+							},
+							py3: {
+								enabled: true,
+							},
+						},
+					}
+
+					python_library_host {
+						name: "lib6",
+						pkg_path: "c/d/",
+						srcs: [
+							"file2.py",
+						],
+						libs: [
+							"lib5",
+						],
+					}
+
+					python_binary_host {
+						name: "bin",
+						pkg_path: "e/",
+						srcs: [
+							"bin.py",
+						],
+						libs: [
+							"lib5",
+						],
+						version: {
+							py3: {
+								enabled: true,
+								srcs: [
+									"file4.py",
+								],
+								libs: [
+									"lib6",
+								],
+							},
+						},
+					}`,
+				),
+				filepath.Join("dir", "file1.py"): nil,
+				filepath.Join("dir", "file2.py"): nil,
+				filepath.Join("dir", "bin.py"):   nil,
+				filepath.Join("dir", "file4.py"): nil,
+				stubTemplateHost: []byte(`PYTHON_BINARY = '%interpreter%'
+				MAIN_FILE = '%main%'`),
+			},
+			expectedBinaries: []pyBinary{
+				{
+					name:          "bin",
+					actualVersion: "PY3",
+					pyRunfiles: []string{
+						"runfiles/e/bin.py",
+						"runfiles/e/file4.py",
+					},
+					depsPyRunfiles: []string{
+						"runfiles/a/b/file1.py",
+						"runfiles/c/d/file2.py",
+					},
+					parSpec: "-P runfiles/e -C dir/ -l @prefix@/.intermediates/dir/bin/PY3/dir_.list",
+					depsParSpecs: []string{
+						"-P runfiles/a/b -C dir/ -l @prefix@/.intermediates/dir/lib5/PY3/dir_.list",
+						"-P runfiles/c/d -C dir/ -l @prefix@/.intermediates/dir/lib6/PY3/dir_.list",
+					},
+				},
+			},
+		},
+	}
+)
+
+func TestPythonModule(t *testing.T) {
+	config, buildDir := setupBuildEnv(t)
+	defer tearDownBuildEnv()
+	android.TestPreDepsMutators(func(ctx android.RegisterMutatorsContext) {
+		ctx.BottomUp("version_split", versionSplitMutator()).Parallel()
+	})
+	for _, d := range data {
+		t.Run(d.desc, func(t *testing.T) {
+			ctx := blueprint.NewContext()
+			android.RegisterTestMutators(ctx)
+			ctx.RegisterModuleType("python_library_host", PythonLibraryHostFactory)
+			ctx.RegisterModuleType("python_binary_host", PythonBinaryHostFactory)
+			ctx.MockFileSystem(d.mockFiles)
+			_, testErrs := ctx.ParseBlueprintsFiles(bpFile)
+			fail(t, testErrs)
+			_, actErrs := ctx.PrepareBuildActions(config)
+			if len(actErrs) > 0 {
+				testErrs = append(testErrs, expectErrors(t, actErrs, d.errors)...)
+			} else {
+				for _, e := range d.expectedBinaries {
+					testErrs = append(testErrs,
+						expectModule(t, ctx, buildDir, e.name,
+							e.actualVersion,
+							e.pyRunfiles, e.depsPyRunfiles,
+							e.parSpec, e.depsParSpecs)...)
+				}
+			}
+			fail(t, testErrs)
+		})
+	}
+}
+
+func expectErrors(t *testing.T, actErrs []error, expErrs []string) (testErrs []error) {
+	actErrStrs := []string{}
+	for _, v := range actErrs {
+		actErrStrs = append(actErrStrs, v.Error())
+	}
+	sort.Strings(actErrStrs)
+	if len(actErrStrs) != len(expErrs) {
+		t.Errorf("got (%d) errors, expected (%d) errors!", len(actErrStrs), len(expErrs))
+		for _, v := range actErrStrs {
+			testErrs = append(testErrs, errors.New(v))
+		}
+	} else {
+		sort.Strings(expErrs)
+		for i, v := range actErrStrs {
+			if v != expErrs[i] {
+				testErrs = append(testErrs, errors.New(v))
+			}
+		}
+	}
+
+	return
+}
+
+func expectModule(t *testing.T, ctx *blueprint.Context, buildDir, name, variant string,
+	expPyRunfiles, expDepsPyRunfiles []string,
+	expParSpec string, expDepsParSpecs []string) (testErrs []error) {
+	module := findModule(ctx, name, variant)
+	if module == nil {
+		t.Fatalf("failed to find module %s!", name)
+	}
+
+	base, baseOk := module.(*pythonBaseModule)
+	if !baseOk {
+		t.Fatalf("%s is not Python module!", name)
+	}
+	sub, subOk := base.subModule.(*PythonBinary)
+	if !subOk {
+		t.Fatalf("%s is not Python binary!", name)
+	}
+
+	actPyRunfiles := []string{}
+	for _, path := range base.srcsPathMappings {
+		actPyRunfiles = append(actPyRunfiles, path.dest)
+	}
+
+	if !reflect.DeepEqual(actPyRunfiles, expPyRunfiles) {
+		testErrs = append(testErrs, errors.New(fmt.Sprintf(
+			`binary "%s" variant "%s" has unexpected pyRunfiles: %q!`,
+			base.Name(),
+			base.properties.ActualVersion,
+			actPyRunfiles)))
+	}
+
+	if !reflect.DeepEqual(sub.depsPyRunfiles, expDepsPyRunfiles) {
+		testErrs = append(testErrs, errors.New(fmt.Sprintf(
+			`binary "%s" variant "%s" has unexpected depsPyRunfiles: %q!`,
+			base.Name(),
+			base.properties.ActualVersion,
+			sub.depsPyRunfiles)))
+	}
+
+	if base.parSpec.soongParArgs() != strings.Replace(expParSpec, "@prefix@", buildDir, 1) {
+		testErrs = append(testErrs, errors.New(fmt.Sprintf(
+			`binary "%s" variant "%s" has unexpected parSpec: %q!`,
+			base.Name(),
+			base.properties.ActualVersion,
+			base.parSpec.soongParArgs())))
+	}
+
+	actDepsParSpecs := []string{}
+	for i, p := range sub.depsParSpecs {
+		actDepsParSpecs = append(actDepsParSpecs, p.soongParArgs())
+		expDepsParSpecs[i] = strings.Replace(expDepsParSpecs[i], "@prefix@", buildDir, 1)
+	}
+
+	if !reflect.DeepEqual(actDepsParSpecs, expDepsParSpecs) {
+		testErrs = append(testErrs, errors.New(fmt.Sprintf(
+			`binary "%s" variant "%s" has unexpected depsParSpecs: %q!`,
+			base.Name(),
+			base.properties.ActualVersion,
+			actDepsParSpecs)))
+	}
+
+	return
+}
+
+func setupBuildEnv(t *testing.T) (config android.Config, buildDir string) {
+	buildDir, err := ioutil.TempDir("", buildNamePrefix)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	config = android.TestConfig(buildDir)
+
+	return
+}
+
+func tearDownBuildEnv() {
+	os.RemoveAll(buildNamePrefix)
+}
+
+func findModule(ctx *blueprint.Context, name, variant string) blueprint.Module {
+	var ret blueprint.Module
+	ctx.VisitAllModules(func(m blueprint.Module) {
+		if ctx.ModuleName(m) == name && ctx.ModuleSubDir(m) == variant {
+			ret = m
+		}
+	})
+	return ret
+}
+
+func fail(t *testing.T, errs []error) {
+	if len(errs) > 0 {
+		for _, err := range errs {
+			t.Error(err)
+		}
+		t.FailNow()
+	}
+}
diff --git a/python/scripts/stub_template_host.txt b/python/scripts/stub_template_host.txt
new file mode 100644
index 00000000..b90a28b5
--- /dev/null
+++ b/python/scripts/stub_template_host.txt
@@ -0,0 +1,91 @@
+#!/usr/bin/env python
+
+import os
+import re
+import tempfile
+import shutil
+import sys
+import subprocess
+import zipfile
+
+PYTHON_BINARY = '%interpreter%'
+MAIN_FILE = '%main%'
+PYTHON_PATH = 'PYTHONPATH'
+ZIP_RUNFILES_DIRECTORY_NAME = 'runfiles'
+
+def SearchPathEnv(name):
+  search_path = os.getenv('PATH', os.defpath).split(os.pathsep)
+  for directory in search_path:
+    if directory == '': continue
+    path = os.path.join(directory, name)
+    if os.path.islink(path):
+      path = os.path.realpath(path)
+    # Check if path is actual executable file.
+    if os.path.isfile(path) and os.access(path, os.X_OK):
+      return path
+  return None
+
+def FindPythonBinary():
+  if PYTHON_BINARY.startswith('/'):
+    # Case 1: Python interpreter is directly provided with absolute path.
+    return PYTHON_BINARY
+  else:
+    # Case 2: Find Python interpreter through environment variable: PATH.
+    return SearchPathEnv(PYTHON_BINARY)
+
+# Create the runfiles tree by extracting the zip file
+def ExtractRunfiles():
+  temp_dir = tempfile.mkdtemp("", "Soong.python_")
+  zf = zipfile.ZipFile(os.path.dirname(__file__))
+  zf.extractall(temp_dir)
+  return os.path.join(temp_dir, ZIP_RUNFILES_DIRECTORY_NAME)
+
+def Main():
+  args = sys.argv[1:]
+
+  new_env = {}
+
+  try:
+    runfiles_path = ExtractRunfiles()
+
+    # Add runfiles path to PYTHONPATH.
+    python_path_entries = [runfiles_path]
+
+    # Add top dirs within runfiles path to PYTHONPATH.
+    top_entries = [os.path.join(runfiles_path, i) for i in os.listdir(runfiles_path)]
+    top_pkg_dirs = [i for i in top_entries if os.path.isdir(i)]
+    python_path_entries += top_pkg_dirs
+
+    old_python_path = os.environ.get(PYTHON_PATH)
+    separator = ':'
+    new_python_path = separator.join(python_path_entries)
+
+    # Copy old PYTHONPATH.
+    if old_python_path:
+      new_python_path += separator + old_python_path
+    new_env[PYTHON_PATH] = new_python_path
+
+    # Now look for main python source file.
+    main_filepath = os.path.join(runfiles_path, MAIN_FILE)
+    assert os.path.exists(main_filepath), \
+           'Cannot exec() %r: file not found.' % main_filepath
+    assert os.access(main_filepath, os.R_OK), \
+           'Cannot exec() %r: file not readable.' % main_filepath
+
+    python_program = FindPythonBinary()
+    if python_program is None:
+      raise AssertionError('Could not find python binary: ' + PYTHON_BINARY)
+    args = [python_program, main_filepath] + args
+
+    os.environ.update(new_env)
+
+    sys.stdout.flush()
+    retCode = subprocess.call(args)
+    exit(retCode)
+  except:
+    raise
+  finally:
+    shutil.rmtree(os.path.dirname(runfiles_path), True)
+
+if __name__ == '__main__':
+  Main()