cpython/Lib/distutils/msvc9compiler.py

"""distutils.msvc9compiler

Contains MSVCCompiler, an implementation of the abstract CCompiler class
for the Microsoft Visual Studio 2008.

The module is compatible with VS 2005 and VS 2008. You can find legacy support
for older versions of VS in distutils.msvccompiler.
"""

# Written by Perry Stoll
# hacked by Robin Becker and Thomas Heller to do a better job of
#   finding DevStudio (through the registry)
# ported to VS2005 and VS 2008 by Christian Heimes

__revision__ = "$Id$"

import os
import subprocess
import sys
import re

from distutils.errors import DistutilsExecError, DistutilsPlatformError, \
                             CompileError, LibError, LinkError
from distutils.ccompiler import CCompiler, gen_preprocess_options, \
                                gen_lib_options
from distutils import log
from distutils.util import get_platform

import winreg

RegOpenKeyEx = winreg.OpenKeyEx
RegEnumKey = winreg.EnumKey
RegEnumValue = winreg.EnumValue
RegError = winreg.error

HKEYS = (winreg.HKEY_USERS,
         winreg.HKEY_CURRENT_USER,
         winreg.HKEY_LOCAL_MACHINE,
         winreg.HKEY_CLASSES_ROOT)

NATIVE_WIN64 = (sys.platform == 'win32' and sys.maxsize > 2**32)
if NATIVE_WIN64:
    # Visual C++ is a 32-bit application, so we need to look in
    # the corresponding registry branch, if we're running a
    # 64-bit Python on Win64
    VS_BASE = r"Software\Wow6432Node\Microsoft\VisualStudio\%0.1f"
    WINSDK_BASE = r"Software\Wow6432Node\Microsoft\Microsoft SDKs\Windows"
    NET_BASE = r"Software\Wow6432Node\Microsoft\.NETFramework"
else:
    VS_BASE = r"Software\Microsoft\VisualStudio\%0.1f"
    WINSDK_BASE = r"Software\Microsoft\Microsoft SDKs\Windows"
    NET_BASE = r"Software\Microsoft\.NETFramework"

# A map keyed by get_platform() return values to values accepted by
# 'vcvarsall.bat'.  Note a cross-compile may combine these (eg, 'x86_amd64' is
# the param to cross-compile on x86 targetting amd64.)
PLAT_TO_VCVARS = {
    'win32' : 'x86',
    'win-amd64' : 'amd64',
    'win-ia64' : 'ia64',
}

class Reg:
    """Helper class to read values from the registry
    """

    def get_value(cls, path, key):
        for base in HKEYS:
            d = cls.read_values(base, path)
            if d and key in d:
                return d[key]
        raise KeyError(key)
    get_value = classmethod(get_value)

    def read_keys(cls, base, key):
        """Return list of registry keys."""
        try:
            handle = RegOpenKeyEx(base, key)
        except RegError:
            return None
        L = []
        i = 0
        while True:
            try:
                k = RegEnumKey(handle, i)
            except RegError:
                break
            L.append(k)
            i += 1
        return L
    read_keys = classmethod(read_keys)

    def read_values(cls, base, key):
        """Return dict of registry keys and values.

        All names are converted to lowercase.
        """
        try:
            handle = RegOpenKeyEx(base, key)
        except RegError:
            return None
        d = {}
        i = 0
        while True:
            try:
                name, value, type = RegEnumValue(handle, i)
            except RegError:
                break
            name = name.lower()
            d[cls.convert_mbcs(name)] = cls.convert_mbcs(value)
            i += 1
        return d
    read_values = classmethod(read_values)

    def convert_mbcs(s):
        dec = getattr(s, "decode", None)
        if dec is not None:
            try:
                s = dec("mbcs")
            except UnicodeError:
                pass
        return s
    convert_mbcs = staticmethod(convert_mbcs)

class MacroExpander:

    def __init__(self, version):
        self.macros = {}
        self.vsbase = VS_BASE % version
        self.load_macros(version)

    def set_macro(self, macro, path, key):
        self.macros["$(%s)" % macro] = Reg.get_value(path, key)

    def load_macros(self, version):
        self.set_macro("VCInstallDir", self.vsbase + r"\Setup\VC", "productdir")
        self.set_macro("VSInstallDir", self.vsbase + r"\Setup\VS", "productdir")
        self.set_macro("FrameworkDir", NET_BASE, "installroot")
        try:
            if version >= 8.0:
                self.set_macro("FrameworkSDKDir", NET_BASE,
                               "sdkinstallrootv2.0")
            else:
                raise KeyError("sdkinstallrootv2.0")
        except KeyError:
            raise DistutilsPlatformError(
            """Python was built with Visual Studio 2008;
extensions must be built with a compiler than can generate compatible binaries.
Visual Studio 2008 was not found on this system. If you have Cygwin installed,
you can try compiling with MingW32, by passing "-c mingw32" to setup.py.""")

        if version >= 9.0:
            self.set_macro("FrameworkVersion", self.vsbase, "clr version")
            self.set_macro("WindowsSdkDir", WINSDK_BASE, "currentinstallfolder")
        else:
            p = r"Software\Microsoft\NET Framework Setup\Product"
            for base in HKEYS:
                try:
                    h = RegOpenKeyEx(base, p)
                except RegError:
                    continue
                key = RegEnumKey(h, 0)
                d = Reg.get_value(base, r"%s\%s" % (p, key))
                self.macros["$(FrameworkVersion)"] = d["version"]

    def sub(self, s):
        for k, v in self.macros.items():
            s = s.replace(k, v)
        return s

def get_build_version():
    """Return the version of MSVC that was used to build Python.

    For Python 2.3 and up, the version number is included in
    sys.version.  For earlier versions, assume the compiler is MSVC 6.
    """
    prefix = "MSC v."
    i = sys.version.find(prefix)
    if i == -1:
        return 6
    i = i + len(prefix)
    s, rest = sys.version[i:].split(" ", 1)
    majorVersion = int(s[:-2]) - 6
    minorVersion = int(s[2:3]) / 10.0
    # I don't think paths are affected by minor version in version 6
    if majorVersion == 6:
        minorVersion = 0
    if majorVersion >= 6:
        return majorVersion + minorVersion
    # else we don't know what version of the compiler this is
    return None

def normalize_and_reduce_paths(paths):
    """Return a list of normalized paths with duplicates removed.

    The current order of paths is maintained.
    """
    # Paths are normalized so things like:  /a and /a/ aren't both preserved.
    reduced_paths = []
    for p in paths:
        np = os.path.normpath(p)
        # XXX(nnorwitz): O(n**2), if reduced_paths gets long perhaps use a set.
        if np not in reduced_paths:
            reduced_paths.append(np)
    return reduced_paths

def removeDuplicates(variable):
    """Remove duplicate values of an environment variable.
    """
    oldList = variable.split(os.pathsep)
    newList = []
    for i in oldList:
        if i not in newList:
            newList.append(i)
    newVariable = os.pathsep.join(newList)
    return newVariable

def find_vcvarsall(version):
    """Find the vcvarsall.bat file

    At first it tries to find the productdir of VS 2008 in the registry. If
    that fails it falls back to the VS90COMNTOOLS env var.
    """
    vsbase = VS_BASE % version
    try:
        productdir = Reg.get_value(r"%s\Setup\VC" % vsbase,
                                   "productdir")
    except KeyError:
        log.debug("Unable to find productdir in registry")
        productdir = None

    if not productdir or not os.path.isdir(productdir):
        toolskey = "VS%0.f0COMNTOOLS" % version
        toolsdir = os.environ.get(toolskey, None)

        if toolsdir and os.path.isdir(toolsdir):
            productdir = os.path.join(toolsdir, os.pardir, os.pardir, "VC")
            productdir = os.path.abspath(productdir)
            if not os.path.isdir(productdir):
                log.debug("%s is not a valid directory" % productdir)
                return None
        else:
            log.debug("Env var %s is not set or invalid" % toolskey)
    if not productdir:
        log.debug("No productdir found")
        return None
    vcvarsall = os.path.join(productdir, "vcvarsall.bat")
    if os.path.isfile(vcvarsall):
        return vcvarsall
    log.debug("Unable to find vcvarsall.bat")
    return None

def query_vcvarsall(version, arch="x86"):
    """Launch vcvarsall.bat and read the settings from its environment
    """
    vcvarsall = find_vcvarsall(version)
    interesting = set(("include", "lib", "libpath", "path"))
    result = {}

    if vcvarsall is None:
        raise DistutilsPlatformError("Unable to find vcvarsall.bat")
    log.debug("Calling 'vcvarsall.bat %s' (version=%s)", arch, version)
    popen = subprocess.Popen('"%s" %s & set' % (vcvarsall, arch),
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE)

    stdout, stderr = popen.communicate()
    if popen.wait() != 0:
        raise DistutilsPlatformError(stderr.decode("mbcs"))

    stdout = stdout.decode("mbcs")
    for line in stdout.split("\n"):
        line = Reg.convert_mbcs(line)
        if '=' not in line:
            continue
        line = line.strip()
        key, value = line.split('=', 1)
        key = key.lower()
        if key in interesting:
            if value.endswith(os.pathsep):
                value = value[:-1]
            result[key] = removeDuplicates(value)

    if len(result) != len(interesting):
        raise ValueError(str(list(result.keys())))

    return result

# More globals
VERSION = get_build_version()
if VERSION < 8.0:
    raise DistutilsPlatformError("VC %0.1f is not supported by this module" % VERSION)
# MACROS = MacroExpander(VERSION)

class MSVCCompiler(CCompiler) :
    """Concrete class that implements an interface to Microsoft Visual C++,
       as defined by the CCompiler abstract class."""

    compiler_type = 'msvc'

    # Just set this so CCompiler's constructor doesn't barf.  We currently
    # don't use the 'set_executables()' bureaucracy provided by CCompiler,
    # as it really isn't necessary for this sort of single-compiler class.
    # Would be nice to have a consistent interface with UnixCCompiler,
    # though, so it's worth thinking about.
    executables = {}

    # Private class data (need to distinguish C from C++ source for compiler)
    _c_extensions = ['.c']
    _cpp_extensions = ['.cc', '.cpp', '.cxx']
    _rc_extensions = ['.rc']
    _mc_extensions = ['.mc']

    # Needed for the filename generation methods provided by the
    # base class, CCompiler.
    src_extensions = (_c_extensions + _cpp_extensions +
                      _rc_extensions + _mc_extensions)
    res_extension = '.res'
    obj_extension = '.obj'
    static_lib_extension = '.lib'
    shared_lib_extension = '.dll'
    static_lib_format = shared_lib_format = '%s%s'
    exe_extension = '.exe'

    def __init__(self, verbose=0, dry_run=0, force=0):
        CCompiler.__init__ (self, verbose, dry_run, force)
        self.__version = VERSION
        self.__root = r"Software\Microsoft\VisualStudio"
        # self.__macros = MACROS
        self.__paths = []
        # target platform (.plat_name is consistent with 'bdist')
        self.plat_name = None
        self.__arch = None # deprecated name
        self.initialized = False

    def initialize(self, plat_name=None):
        # multi-init means we would need to check platform same each time...
        assert not self.initialized, "don't init multiple times"
        if plat_name is None:
            plat_name = get_platform()
        # sanity check for platforms to prevent obscure errors later.
        ok_plats = 'win32', 'win-amd64', 'win-ia64'
        if plat_name not in ok_plats:
            raise DistutilsPlatformError("--plat-name must be one of %s" %
                                         (ok_plats,))

        if "DISTUTILS_USE_SDK" in os.environ and "MSSdk" in os.environ and self.find_exe("cl.exe"):
            # Assume that the SDK set up everything alright; don't try to be
            # smarter
            self.cc = "cl.exe"
            self.linker = "link.exe"
            self.lib = "lib.exe"
            self.rc = "rc.exe"
            self.mc = "mc.exe"
        else:
            # On x86, 'vcvars32.bat amd64' creates an env that doesn't work;
            # to cross compile, you use 'x86_amd64'.
            # On AMD64, 'vcvars32.bat amd64' is a native build env; to cross
            # compile use 'x86' (ie, it runs the x86 compiler directly)
            # No idea how itanium handles this, if at all.
            if plat_name == get_platform() or plat_name == 'win32':
                # native build or cross-compile to win32
                plat_spec = PLAT_TO_VCVARS[plat_name]
            else:
                # cross compile from win32 -> some 64bit
                plat_spec = PLAT_TO_VCVARS[get_platform()] + '_' + \
                            PLAT_TO_VCVARS[plat_name]

            vc_env = query_vcvarsall(VERSION, plat_spec)

            self.__paths = vc_env['path'].split(os.pathsep)
            os.environ['lib'] = vc_env['lib']
            os.environ['include'] = vc_env['include']

            if len(self.__paths) == 0:
                raise DistutilsPlatformError("Python was built with %s, "
                       "and extensions need to be built with the same "
                       "version of the compiler, but it isn't installed."
                       % self.__product)

            self.cc = self.find_exe("cl.exe")
            self.linker = self.find_exe("link.exe")
            self.lib = self.find_exe("lib.exe")
            self.rc = self.find_exe("rc.exe")   # resource compiler
            self.mc = self.find_exe("mc.exe")   # message compiler
            #self.set_path_env_var('lib')
            #self.set_path_env_var('include')

        # extend the MSVC path with the current path
        try:
            for p in os.environ['path'].split(';'):
                self.__paths.append(p)
        except KeyError:
            pass
        self.__paths = normalize_and_reduce_paths(self.__paths)
        os.environ['path'] = ";".join(self.__paths)

        self.preprocess_options = None
        if self.__arch == "x86":
            self.compile_options = [ '/nologo', '/Ox', '/MD', '/W3',
                                     '/DNDEBUG']
            self.compile_options_debug = ['/nologo', '/Od', '/MDd', '/W3',
                                          '/Z7', '/D_DEBUG']
        else:
            # Win64
            self.compile_options = [ '/nologo', '/Ox', '/MD', '/W3', '/GS-' ,
                                     '/DNDEBUG']
            self.compile_options_debug = ['/nologo', '/Od', '/MDd', '/W3', '/GS-',
                                          '/Z7', '/D_DEBUG']

        self.ldflags_shared = ['/DLL', '/nologo', '/INCREMENTAL:NO']
        if self.__version >= 7:
            self.ldflags_shared_debug = [
                '/DLL', '/nologo', '/INCREMENTAL:no', '/DEBUG', '/pdb:None'
                ]
        self.ldflags_static = [ '/nologo']

        self.initialized = True

    # -- Worker methods ------------------------------------------------

    def object_filenames(self,
                         source_filenames,
                         strip_dir=0,
                         output_dir=''):
        # Copied from ccompiler.py, extended to return .res as 'object'-file
        # for .rc input file
        if output_dir is None: output_dir = ''
        obj_names = []
        for src_name in source_filenames:
            (base, ext) = os.path.splitext (src_name)
            base = os.path.splitdrive(base)[1] # Chop off the drive
            base = base[os.path.isabs(base):]  # If abs, chop off leading /
            if ext not in self.src_extensions:
                # Better to raise an exception instead of silently continuing
                # and later complain about sources and targets having
                # different lengths
                raise CompileError ("Don't know how to compile %s" % src_name)
            if strip_dir:
                base = os.path.basename (base)
            if ext in self._rc_extensions:
                obj_names.append (os.path.join (output_dir,
                                                base + self.res_extension))
            elif ext in self._mc_extensions:
                obj_names.append (os.path.join (output_dir,
                                                base + self.res_extension))
            else:
                obj_names.append (os.path.join (output_dir,
                                                base + self.obj_extension))
        return obj_names


    def compile(self, sources,
                output_dir=None, macros=None, include_dirs=None, debug=0,
                extra_preargs=None, extra_postargs=None, depends=None):

        if not self.initialized:
            self.initialize()
        compile_info = self._setup_compile(output_dir, macros, include_dirs,
                                           sources, depends, extra_postargs)
        macros, objects, extra_postargs, pp_opts, build = compile_info

        compile_opts = extra_preargs or []
        compile_opts.append ('/c')
        if debug:
            compile_opts.extend(self.compile_options_debug)
        else:
            compile_opts.extend(self.compile_options)

        for obj in objects:
            try:
                src, ext = build[obj]
            except KeyError:
                continue
            if debug:
                # pass the full pathname to MSVC in debug mode,
                # this allows the debugger to find the source file
                # without asking the user to browse for it
                src = os.path.abspath(src)

            if ext in self._c_extensions:
                input_opt = "/Tc" + src
            elif ext in self._cpp_extensions:
                input_opt = "/Tp" + src
            elif ext in self._rc_extensions:
                # compile .RC to .RES file
                input_opt = src
                output_opt = "/fo" + obj
                try:
                    self.spawn([self.rc] + pp_opts +
                               [output_opt] + [input_opt])
                except DistutilsExecError as msg:
                    raise CompileError(msg)
                continue
            elif ext in self._mc_extensions:
                # Compile .MC to .RC file to .RES file.
                #   * '-h dir' specifies the directory for the
                #     generated include file
                #   * '-r dir' specifies the target directory of the
                #     generated RC file and the binary message resource
                #     it includes
                #
                # For now (since there are no options to change this),
                # we use the source-directory for the include file and
                # the build directory for the RC file and message
                # resources. This works at least for win32all.
                h_dir = os.path.dirname(src)
                rc_dir = os.path.dirname(obj)
                try:
                    # first compile .MC to .RC and .H file
                    self.spawn([self.mc] +
                               ['-h', h_dir, '-r', rc_dir] + [src])
                    base, _ = os.path.splitext (os.path.basename (src))
                    rc_file = os.path.join (rc_dir, base + '.rc')
                    # then compile .RC to .RES file
                    self.spawn([self.rc] +
                               ["/fo" + obj] + [rc_file])

                except DistutilsExecError as msg:
                    raise CompileError(msg)
                continue
            else:
                # how to handle this file?
                raise CompileError("Don't know how to compile %s to %s"
                                   % (src, obj))

            output_opt = "/Fo" + obj
            try:
                self.spawn([self.cc] + compile_opts + pp_opts +
                           [input_opt, output_opt] +
                           extra_postargs)
            except DistutilsExecError as msg:
                raise CompileError(msg)

        return objects


    def create_static_lib(self,
                          objects,
                          output_libname,
                          output_dir=None,
                          debug=0,
                          target_lang=None):

        if not self.initialized:
            self.initialize()
        (objects, output_dir) = self._fix_object_args(objects, output_dir)
        output_filename = self.library_filename(output_libname,
                                                output_dir=output_dir)

        if self._need_link(objects, output_filename):
            lib_args = objects + ['/OUT:' + output_filename]
            if debug:
                pass # XXX what goes here?
            try:
                self.spawn([self.lib] + lib_args)
            except DistutilsExecError as msg:
                raise LibError(msg)
        else:
            log.debug("skipping %s (up-to-date)", output_filename)


    def link(self,
             target_desc,
             objects,
             output_filename,
             output_dir=None,
             libraries=None,
             library_dirs=None,
             runtime_library_dirs=None,
             export_symbols=None,
             debug=0,
             extra_preargs=None,
             extra_postargs=None,
             build_temp=None,
             target_lang=None):

        if not self.initialized:
            self.initialize()
        (objects, output_dir) = self._fix_object_args(objects, output_dir)
        fixed_args = self._fix_lib_args(libraries, library_dirs,
                                        runtime_library_dirs)
        (libraries, library_dirs, runtime_library_dirs) = fixed_args

        if runtime_library_dirs:
            self.warn ("I don't know what to do with 'runtime_library_dirs': "
                       + str (runtime_library_dirs))

        lib_opts = gen_lib_options(self,
                                   library_dirs, runtime_library_dirs,
                                   libraries)
        if output_dir is not None:
            output_filename = os.path.join(output_dir, output_filename)

        if self._need_link(objects, output_filename):
            if target_desc == CCompiler.EXECUTABLE:
                if debug:
                    ldflags = self.ldflags_shared_debug[1:]
                else:
                    ldflags = self.ldflags_shared[1:]
            else:
                if debug:
                    ldflags = self.ldflags_shared_debug
                else:
                    ldflags = self.ldflags_shared

            export_opts = []
            for sym in (export_symbols or []):
                export_opts.append("/EXPORT:" + sym)

            ld_args = (ldflags + lib_opts + export_opts +
                       objects + ['/OUT:' + output_filename])

            # The MSVC linker generates .lib and .exp files, which cannot be
            # suppressed by any linker switches. The .lib files may even be
            # needed! Make sure they are generated in the temporary build
            # directory. Since they have different names for debug and release
            # builds, they can go into the same directory.
            build_temp = os.path.dirname(objects[0])
            if export_symbols is not None:
                (dll_name, dll_ext) = os.path.splitext(
                    os.path.basename(output_filename))
                implib_file = os.path.join(
                    build_temp,
                    self.library_filename(dll_name))
                ld_args.append ('/IMPLIB:' + implib_file)

            # Embedded manifests are recommended - see MSDN article titled
            # "How to: Embed a Manifest Inside a C/C++ Application"
            # (currently at http://msdn2.microsoft.com/en-us/library/ms235591(VS.80).aspx)
            # Ask the linker to generate the manifest in the temp dir, so
            # we can embed it later.
            temp_manifest = os.path.join(
                    build_temp,
                    os.path.basename(output_filename) + ".manifest")
            ld_args.append('/MANIFESTFILE:' + temp_manifest)

            if extra_preargs:
                ld_args[:0] = extra_preargs
            if extra_postargs:
                ld_args.extend(extra_postargs)

            self.mkpath(os.path.dirname(output_filename))
            try:
                self.spawn([self.linker] + ld_args)
            except DistutilsExecError as msg:
                raise LinkError(msg)

            # embed the manifest
            # XXX - this is somewhat fragile - if mt.exe fails, distutils
            # will still consider the DLL up-to-date, but it will not have a
            # manifest.  Maybe we should link to a temp file?  OTOH, that
            # implies a build environment error that shouldn't go undetected.
            if target_desc == CCompiler.EXECUTABLE:
                mfid = 1
            else:
                mfid = 2
                # Remove references to the Visual C runtime
                self._remove_visual_c_ref(temp_manifest)
            out_arg = '-outputresource:%s;%s' % (output_filename, mfid)
            try:
                self.spawn(['mt.exe', '-nologo', '-manifest',
                            temp_manifest, out_arg])
            except DistutilsExecError as msg:
                raise LinkError(msg)
        else:
            log.debug("skipping %s (up-to-date)", output_filename)

    def _remove_visual_c_ref(self, manifest_file):
        try:
            # Remove references to the Visual C runtime, so they will
            # fall through to the Visual C dependency of Python.exe.
            # This way, when installed for a restricted user (e.g.
            # runtimes are not in WinSxS folder, but in Python's own
            # folder), the runtimes do not need to be in every folder
            # with .pyd's.
            manifest_f = open(manifest_file)
            try:
                manifest_buf = manifest_f.read()
            finally:
                manifest_f.close()
            pattern = re.compile(
                r"""<assemblyIdentity.*?name=("|')Microsoft\."""\
                r"""VC\d{2}\.CRT("|').*?(/>|</assemblyIdentity>)""",
                re.DOTALL)
            manifest_buf = re.sub(pattern, "", manifest_buf)
            pattern = "<dependentAssembly>\s*</dependentAssembly>"
            manifest_buf = re.sub(pattern, "", manifest_buf)
            manifest_f = open(manifest_file, 'w')
            try:
                manifest_f.write(manifest_buf)
            finally:
                manifest_f.close()
        except IOError:
            pass

    # -- Miscellaneous methods -----------------------------------------
    # These are all used by the 'gen_lib_options() function, in
    # ccompiler.py.

    def library_dir_option(self, dir):
        return "/LIBPATH:" + dir

    def runtime_library_dir_option(self, dir):
        raise DistutilsPlatformError(
              "don't know how to set runtime library search path for MSVC++")

    def library_option(self, lib):
        return self.library_filename(lib)


    def find_library_file(self, dirs, lib, debug=0):
        # Prefer a debugging library if found (and requested), but deal
        # with it if we don't have one.
        if debug:
            try_names = [lib + "_d", lib]
        else:
            try_names = [lib]
        for dir in dirs:
            for name in try_names:
                libfile = os.path.join(dir, self.library_filename (name))
                if os.path.exists(libfile):
                    return libfile
        else:
            # Oops, didn't find it in *any* of 'dirs'
            return None

    # Helper methods for using the MSVC registry settings

    def find_exe(self, exe):
        """Return path to an MSVC executable program.

        Tries to find the program in several places: first, one of the
        MSVC program search paths from the registry; next, the directories
        in the PATH environment variable.  If any of those work, return an
        absolute path that is known to exist.  If none of them work, just
        return the original program name, 'exe'.
        """
        for p in self.__paths:
            fn = os.path.join(os.path.abspath(p), exe)
            if os.path.isfile(fn):
                return fn

        # didn't find it; try existing path
        for p in os.environ['Path'].split(';'):
            fn = os.path.join(os.path.abspath(p),exe)
            if os.path.isfile(fn):
                return fn

        return exe