How to use the py.error function in py

for path in paths]
                tryadd = '', '.exe', '.com', '.bat' # XXX add more?
            else:
                paths = py.std.os.environ['PATH'].split(':')
                tryadd = ('',)

            for x in paths:
                for addext in tryadd:
                    p = py.path.local(x).join(name, abs=True) + addext
                    try:
                        if p.check(file=1):
                            if checker:
                                if not checker(p):
                                    continue
                            return p
                    except py.error.EACCES:
                        pass
        return None
    sysfind = classmethod(sysfind)

BuiltinAssertionError.__init__(self, *args)
        if args: 
            try:
                self.msg = str(args[0])
            except (KeyboardInterrupt, SystemExit):
                raise
            except:
                self.msg = "<[broken __repr__] %s at %0xd>" %(
                    args[0].__class__, id(args[0]))
            
        else: 
            f = sys._getframe(1)
            try:
                source = py.code.Frame(f).statement
                source = str(source.deindent()).strip()
            except py.error.ENOENT:
                source = None
                # this can also occur during reinterpretation, when the
                # co_filename is set to "".
            if source:
                self.msg = exprinfo.interpret(source, f, should_fail=True)
                if not self.args:
                    self.args = (self.msg,)
            else:
                self.msg = None

def test_listdir(self, path1):
        l = path1.listdir()
        assert path1.join('sampledir') in l
        assert path1.join('samplefile') in l
        py.test.raises(py.error.ENOTDIR,
                       "path1.join('samplefile').listdir()")

def dir(self):
            try:
                return self.path.info().kind == 'dir'
            except py.error.Error:
                return self._listdirworks()

def _stat(self):
            try:
                return self._statcache
            except AttributeError:
                try:
                    self._statcache = self.path.stat()
                except py.error.ELOOP:
                    self._statcache = self.path.lstat()
                return self._statcache

def _stat(self):
            try:
                return self._statcache
            except AttributeError:
                try:
                    self._statcache = self.path.stat()
                except py.error.ELOOP:
                    self._statcache = self.path.lstat()
                return self._statcache

def chmod(self, mode, rec=0):
        """ change permissions to the given mode. If mode is an
            integer it directly encodes the os-specific modes.
            if rec is True perform recursively.
        """
        if not isinstance(mode, int):
            raise TypeError("mode %r must be an integer" % (mode,))
        if rec:
            for x in self.visit(rec=rec):
                py.error.checked_call(os.chmod, str(x), mode)
        py.error.checked_call(os.chmod, self.strpath, mode)

def rename(self, target, msg="renamed by py lib invocation"):
        """ rename this path to target with checkin message msg. """
        if getattr(self, 'rev', None) is not None:
            raise py.error.EINVAL(self, "revisions are immutable")
        self._svncmdexecauth('svn move -m "%s" --force "%s" "%s"' %(
                             msg, self._escape(self), self._escape(target)))
        self._norev_delentry(self.dirpath())
        self._norev_delentry(self)

def open(self, mode='r', ensure=False, encoding=None):
        """ return an opened file with the given mode.

        If ensure is True, create parent directories if needed.
        """
        if ensure:
            self.dirpath().ensure(dir=1)
        if encoding:
            return py.error.checked_call(io.open, self.strpath, mode, encoding=encoding)
        return py.error.checked_call(open, self.strpath, mode)

if hold:
                    os.environ[key] = hold
                else:
                    del os.environ[key]
        except py.process.cmdexec.Error:
            e = sys.exc_info()[1]
            strerr = e.err.lower()
            if strerr.find('not found') != -1:
                raise py.error.ENOENT(self)
            elif strerr.find("E200009:") != -1:
                raise py.error.ENOENT(self)
            if (strerr.find('file exists') != -1 or
                strerr.find('file already exists') != -1 or
                strerr.find('w150002:') != -1 or
                strerr.find("can't create directory") != -1):
                raise py.error.EEXIST(strerr) #self)
            raise
        return out