def choose_form(self, number=None, id=None, name=None, xpath=None):
        """
        Set the default form.

        :param number: number of form (starting from zero)
        :param id: value of "id" attribute
        :param name: value of "name" attribute
        :param xpath: XPath query
        :raises: :class:`DataNotFound` if form not found
        :raises: :class:`GrabMisuseError`
            if method is called without parameters

        Selected form will be available via `form` attribute of `Grab`
        instance. All form methods will work with default form.

        Examples::

            # Select second form
            g.choose_form(1)

            # Select by id
            g.choose_form(id="register")

            # Select by name
            g.choose_form(name="signup")

            # Select by xpath
            g.choose_form(xpath='//form[contains(@action, "/submit")]')
        """

        if id is not None:
            try:
                self._lxml_form = self.select('//form[@id="%s"]' % id).node()
            except __HOLE__:
                raise DataNotFound("There is no form with id: %s" % id)
        elif name is not None:
            try:
                self._lxml_form = self.select(
                    '//form[@name="%s"]' % name).node()
            except IndexError:
                raise DataNotFound('There is no form with name: %s' % name)
        elif number is not None:
            try:
                self._lxml_form = self.tree.forms[number]
            except IndexError:
                raise DataNotFound('There is no form with number: %s' % number)
        elif xpath is not None:
            try:
                self._lxml_form = self.select(xpath).node()
            except IndexError:
                raise DataNotFound(
                    'Could not find form with xpath: %s' % xpath)
        else:
            raise GrabMisuseError('choose_form methods requires one of '
                                  '[number, id, name, xpath] arguments')
dataset/ETHPy150Open lorien/grab/grab/document.py/FormExtension.choose_form