def field_for(self, field_id):
for field in self.fields:<EOL><INDENT>if field.id == field_id:<EOL><INDENT>return field<EOL><DEDENT><DEDENT>return None<EOL>
Fetches the field for the given Field ID.

        :param field_id: ID for Field to fetch.
        :return: :class:`ContentTypeField <ContentTypeField>` object.
        :rtype: contentful.ContentTypeField