Submit default form.

        :param submit_name: name of button which should be "clicked" to
            submit form
        :param url: explicitly specify form action url
        :param extra_post: (dict or list of pairs) additional form data which
            will override data automatically extracted from the form.
        :param remove_from_post: list of keys to remove from the submitted data

        Following input elements are automatically processed:

        * input[type="hidden"] - default value
        * select: value of last option
        * radio - ???
        * checkbox - ???

        Multipart forms are correctly recognized by grab library.

def get_form_request(
            self, submit_name=None,
            url=None, extra_post=None, remove_from_post=None):
        """
        Submit default form.

        :param submit_name: name of button which should be "clicked" to
            submit form
        :param url: explicitly specify form action url
        :param extra_post: (dict or list of pairs) additional form data which
            will override data automatically extracted from the form.
        :param remove_from_post: list of keys to remove from the submitted data

        Following input elements are automatically processed:

        * input[type="hidden"] - default value
        * select: value of last option
        * radio - ???
        * checkbox - ???

        Multipart forms are correctly recognized by grab library.
        """

        # pylint: disable=no-member

        post = self.form_fields()

        # Build list of submit buttons which have a name
        submit_controls = {}
        for elem in self.form.inputs:
            if (elem.tag == 'input' and elem.type == 'submit' and
                    elem.get('name') is not None):
                submit_controls[elem.name] = elem

        # All this code need only for one reason:
        # to not send multiple submit keys in form data
        # in real life only this key is submitted whose button
        # was pressed
        if submit_controls:
            # If name of submit control is not given then
            # use the name of first submit control
            if submit_name is None or submit_name not in submit_controls:
                controls = sorted(submit_controls.values(),
                                  key=lambda x: x.name)
                submit_name = controls[0].name

            # Form data should contain only one submit control
            for name in submit_controls:
                if name != submit_name:
                    if name in post:
                        del post[name]

        if url:
            action_url = urljoin(self.url, url)
        else:
            action_url = urljoin(self.url,
                                 self.form.action)

        # Values from `extra_post` should override values in form
        # `extra_post` allows multiple value of one key

        # Process saved values of file fields
        if self.form.method == 'POST':
            if 'multipart' in self.form.get('enctype', ''):
                for key, obj in self._file_fields.items():
                    post[key] = obj

        post_items = list(post.items())
        del post

        if extra_post:
            if isinstance(extra_post, dict):
                extra_post_items = extra_post.items()
            else:
                extra_post_items = extra_post

            # Drop existing post items with such key
            keys_to_drop = set([x for x, y in extra_post_items])
            for key in keys_to_drop:
                post_items = [(x, y) for x, y in post_items if x != key]

            for key, value in extra_post_items:
                post_items.append((key, value))

        if remove_from_post:
            post_items = [(x, y) for x, y in post_items
                          if x not in remove_from_post]

        result = {
            'multipart_post': None,
            'post': None,
            'url': None,
        }

        if self.form.method == 'POST':
            if 'multipart' in self.form.get('enctype', ''):
                result['multipart_post'] = post_items
                #self.grab.setup(multipart_post=post_items)
            else:
                result['post'] = post_items
                #self.grab.setup(post=post_items)
            result['url'] = action_url
            #self.grab.setup(url=action_url)

        else:
            url = action_url.split('?')[0] + '?' + smart_urlencode(post_items)
            result['url'] = url
            #self.grab.setup(url=url)

        return result