.. _topics-request-response: ====================== Requests and Responses ====================== .. module:: scrapy.http :synopsis: Request and Response classes Scrapy uses :class:`Request` and :class:`Response` objects for crawling web sites. Typically, :class:`Request` objects are generated in the spiders and pass across the system until they reach the Downloader, which executes the request and returns a :class:`Response` object which travels back to the spider that issued the request. Both :class:`Request` and :class:`Response` classes have subclasses which add functionality not required in the base classes. These are described below in :ref:`topics-request-response-ref-request-subclasses` and :ref:`topics-request-response-ref-response-subclasses`. Request objects =============== .. class:: Request(url[, callback, method='GET', headers, body, cookies, meta, encoding='utf-8', priority=0, dont_filter=False, errback]) A :class:`Request` object represents an HTTP request, which is usually generated in the Spider and executed by the Downloader, and thus generating a :class:`Response`. :param url: the URL of this request :type url: string :param callback: the function that will be called with the response of this request (once its downloaded) as its first parameter. For more information see :ref:`topics-request-response-ref-request-callback-arguments` below. If a Request doesn't specify a callback, the spider's :meth:`~scrapy.spider.Spider.parse` method will be used. Note that if exceptions are raised during processing, errback is called instead. :type callback: callable :param method: the HTTP method of this request. Defaults to ``'GET'``. :type method: string :param meta: the initial values for the :attr:`Request.meta` attribute. If given, the dict passed in this parameter will be shallow copied. :type meta: dict :param body: the request body. If a ``unicode`` is passed, then it's encoded to ``str`` using the `encoding` passed (which defaults to ``utf-8``). If ``body`` is not given, an empty string is stored. Regardless of the type of this argument, the final value stored will be a ``str`` (never ``unicode`` or ``None``). :type body: str or unicode :param headers: the headers of this request. The dict values can be strings (for single valued headers) or lists (for multi-valued headers). If ``None`` is passed as value, the HTTP header will not be sent at all. :type headers: dict :param cookies: the request cookies. These can be sent in two forms. 1. Using a dict:: request_with_cookies = Request(url="http://www.example.com", cookies={'currency': 'USD', 'country': 'UY'}) 2. Using a list of dicts:: request_with_cookies = Request(url="http://www.example.com", cookies=[{'name': 'currency', 'value': 'USD', 'domain': 'example.com', 'path': '/currency'}]) The latter form allows for customizing the ``domain`` and ``path`` attributes of the cookie. This is only useful if the cookies are saved for later requests. When some site returns cookies (in a response) those are stored in the cookies for that domain and will be sent again in future requests. That's the typical behaviour of any regular web browser. However, if, for some reason, you want to avoid merging with existing cookies you can instruct Scrapy to do so by setting the ``dont_merge_cookies`` key to True in the :attr:`Request.meta`. Example of request without merging cookies:: request_with_cookies = Request(url="http://www.example.com", cookies={'currency': 'USD', 'country': 'UY'}, meta={'dont_merge_cookies': True}) For more info see :ref:`cookies-mw`. :type cookies: dict or list :param encoding: the encoding of this request (defaults to ``'utf-8'``). This encoding will be used to percent-encode the URL and to convert the body to ``str`` (if given as ``unicode``). :type encoding: string :param priority: the priority of this request (defaults to ``0``). The priority is used by the scheduler to define the order used to process requests. Requests with a higher priority value will execute earlier. Negative values are allowed in order to indicate relatively low-priority. :type priority: int :param dont_filter: indicates that this request should not be filtered by the scheduler. This is used when you want to perform an identical request multiple times, to ignore the duplicates filter. Use it with care, or you will get into crawling loops. Default to ``False``. :type dont_filter: boolean :param errback: a function that will be called if any exception was raised while processing the request. This includes pages that failed with 404 HTTP errors and such. It receives a `Twisted Failure`_ instance as first parameter. :type errback: callable .. attribute:: Request.url A string containing the URL of this request. Keep in mind that this attribute contains the escaped URL, so it can differ from the URL passed in the constructor. This attribute is read-only. To change the URL of a Request use :meth:`replace`. .. attribute:: Request.method A string representing the HTTP method in the request. This is guaranteed to be uppercase. Example: ``"GET"``, ``"POST"``, ``"PUT"``, etc .. attribute:: Request.headers A dictionary-like object which contains the request headers. .. attribute:: Request.body A str that contains the request body. This attribute is read-only. To change the body of a Request use :meth:`replace`. .. attribute:: Request.meta A dict that contains arbitrary metadata for this request. This dict is empty for new Requests, and is usually populated by different Scrapy components (extensions, middlewares, etc). So the data contained in this dict depends on the extensions you have enabled. See :ref:`topics-request-meta` for a list of special meta keys recognized by Scrapy. This dict is `shallow copied`_ when the request is cloned using the ``copy()`` or ``replace()`` methods, and can also be accessed, in your spider, from the ``response.meta`` attribute. .. _shallow copied: https://docs.python.org/2/library/copy.html .. method:: Request.copy() Return a new Request which is a copy of this Request. See also: :ref:`topics-request-response-ref-request-callback-arguments`. .. method:: Request.replace([url, method, headers, body, cookies, meta, encoding, dont_filter, callback, errback]) Return a Request object with the same members, except for those members given new values by whichever keyword arguments are specified. The attribute :attr:`Request.meta` is copied by default (unless a new value is given in the ``meta`` argument). See also :ref:`topics-request-response-ref-request-callback-arguments`. .. _topics-request-response-ref-request-callback-arguments: Passing additional data to callback functions --------------------------------------------- The callback of a request is a function that will be called when the response of that request is downloaded. The callback function will be called with the downloaded :class:`Response` object as its first argument. Example:: def parse_page1(self, response): return scrapy.Request("http://www.example.com/some_page.html", callback=self.parse_page2) def parse_page2(self, response): # this would log http://www.example.com/some_page.html self.logger.info("Visited %s", response.url) In some cases you may be interested in passing arguments to those callback functions so you can receive the arguments later, in the second callback. You can use the :attr:`Request.meta` attribute for that. Here's an example of how to pass an item using this mechanism, to populate different fields from different pages:: def parse_page1(self, response): item = MyItem() item['main_url'] = response.url request = scrapy.Request("http://www.example.com/some_page.html", callback=self.parse_page2) request.meta['item'] = item return request def parse_page2(self, response): item = response.meta['item'] item['other_url'] = response.url return item .. _topics-request-meta: Request.meta special keys ========================= The :attr:`Request.meta` attribute can contain any arbitrary data, but there are some special keys recognized by Scrapy and its built-in extensions. Those are: * :reqmeta:`dont_redirect` * :reqmeta:`dont_retry` * :reqmeta:`handle_httpstatus_list` * :reqmeta:`handle_httpstatus_all` * ``dont_merge_cookies`` (see ``cookies`` parameter of :class:`Request` constructor) * :reqmeta:`cookiejar` :reqmeta:`dont_cache` * :reqmeta:`redirect_urls` * :reqmeta:`bindaddress` * :reqmeta:`dont_obey_robotstxt` * :reqmeta:`download_timeout` * :reqmeta:`download_maxsize` * :reqmeta:`proxy` .. reqmeta:: bindaddress bindaddress ----------- The IP of the outgoing IP address to use for the performing the request. .. reqmeta:: download_timeout download_timeout ---------------- The amount of time (in secs) that the downloader will wait before timing out. See also: :setting:`DOWNLOAD_TIMEOUT`. .. _topics-request-response-ref-request-subclasses: Request subclasses ================== Here is the list of built-in :class:`Request` subclasses. You can also subclass it to implement your own custom functionality. FormRequest objects ------------------- The FormRequest class extends the base :class:`Request` with functionality for dealing with HTML forms. It uses `lxml.html forms`_ to pre-populate form fields with form data from :class:`Response` objects. .. _lxml.html forms: http://lxml.de/lxmlhtml.html#forms .. class:: FormRequest(url, [formdata, ...]) The :class:`FormRequest` class adds a new argument to the constructor. The remaining arguments are the same as for the :class:`Request` class and are not documented here. :param formdata: is a dictionary (or iterable of (key, value) tuples) containing HTML Form data which will be url-encoded and assigned to the body of the request. :type formdata: dict or iterable of tuples The :class:`FormRequest` objects support the following class method in addition to the standard :class:`Request` methods: .. classmethod:: FormRequest.from_response(response, [formname=None, formnumber=0, formdata=None, formxpath=None, clickdata=None, dont_click=False, ...]) Returns a new :class:`FormRequest` object with its form field values pre-populated with those found in the HTML ``
`` element contained in the given response. For an example see :ref:`topics-request-response-ref-request-userlogin`. The policy is to automatically simulate a click, by default, on any form control that looks clickable, like a ````. Even though this is quite convenient, and often the desired behaviour, sometimes it can cause problems which could be hard to debug. For example, when working with forms that are filled and/or submitted using javascript, the default :meth:`from_response` behaviour may not be the most appropriate. To disable this behaviour you can set the ``dont_click`` argument to ``True``. Also, if you want to change the control clicked (instead of disabling it) you can also use the ``clickdata`` argument. :param response: the response containing a HTML form which will be used to pre-populate the form fields :type response: :class:`Response` object :param formname: if given, the form with name attribute set to this value will be used. :type formname: string :param formxpath: if given, the first form that matches the xpath will be used. :type formxpath: string :param formnumber: the number of form to use, when the response contains multiple forms. The first one (and also the default) is ``0``. :type formnumber: integer :param formdata: fields to override in the form data. If a field was already present in the response ```` element, its value is overridden by the one passed in this parameter. :type formdata: dict :param clickdata: attributes to lookup the control clicked. If it's not given, the form data will be submitted simulating a click on the first clickable element. In addition to html attributes, the control can be identified by its zero-based index relative to other submittable inputs inside the form, via the ``nr`` attribute. :type clickdata: dict :param dont_click: If True, the form data will be submitted without clicking in any element. :type dont_click: boolean The other parameters of this class method are passed directly to the :class:`FormRequest` constructor. .. versionadded:: 0.10.3 The ``formname`` parameter. .. versionadded:: 0.17 The ``formxpath`` parameter. Request usage examples ---------------------- Using FormRequest to send data via HTTP POST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If you want to simulate a HTML Form POST in your spider and send a couple of key-value fields, you can return a :class:`FormRequest` object (from your spider) like this:: return [FormRequest(url="http://www.example.com/post/action", formdata={'name': 'John Doe', 'age': '27'}, callback=self.after_post)] .. _topics-request-response-ref-request-userlogin: Using FormRequest.from_response() to simulate a user login ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It is usual for web sites to provide pre-populated form fields through ```` elements, such as session related data or authentication tokens (for login pages). When scraping, you'll want these fields to be automatically pre-populated and only override a couple of them, such as the user name and password. You can use the :meth:`FormRequest.from_response` method for this job. Here's an example spider which uses it:: import scrapy class LoginSpider(scrapy.Spider): name = 'example.com' start_urls = ['http://www.example.com/users/login.php'] def parse(self, response): return scrapy.FormRequest.from_response( response, formdata={'username': 'john', 'password': 'secret'}, callback=self.after_login ) def after_login(self, response): # check login succeed before going on if "authentication failed" in response.body: self.logger.error("Login failed") return # continue scraping with authenticated session... Response objects ================ .. class:: Response(url, [status=200, headers, body, flags]) A :class:`Response` object represents an HTTP response, which is usually downloaded (by the Downloader) and fed to the Spiders for processing. :param url: the URL of this response :type url: string :param headers: the headers of this response. The dict values can be strings (for single valued headers) or lists (for multi-valued headers). :type headers: dict :param status: the HTTP status of the response. Defaults to ``200``. :type status: integer :param body: the response body. It must be str, not unicode, unless you're using a encoding-aware :ref:`Response subclass `, such as :class:`TextResponse`. :type body: str :param meta: the initial values for the :attr:`Response.meta` attribute. If given, the dict will be shallow copied. :type meta: dict :param flags: is a list containing the initial values for the :attr:`Response.flags` attribute. If given, the list will be shallow copied. :type flags: list .. attribute:: Response.url A string containing the URL of the response. This attribute is read-only. To change the URL of a Response use :meth:`replace`. .. attribute:: Response.status An integer representing the HTTP status of the response. Example: ``200``, ``404``. .. attribute:: Response.headers A dictionary-like object which contains the response headers. .. attribute:: Response.body A str containing the body of this Response. Keep in mind that Response.body is always a str. If you want the unicode version use :meth:`TextResponse.body_as_unicode` (only available in :class:`TextResponse` and subclasses). This attribute is read-only. To change the body of a Response use :meth:`replace`. .. attribute:: Response.request The :class:`Request` object that generated this response. This attribute is assigned in the Scrapy engine, after the response and the request have passed through all :ref:`Downloader Middlewares `. In particular, this means that: - HTTP redirections will cause the original request (to the URL before redirection) to be assigned to the redirected response (with the final URL after redirection). - Response.request.url doesn't always equal Response.url - This attribute is only available in the spider code, and in the :ref:`Spider Middlewares `, but not in Downloader Middlewares (although you have the Request available there by other means) and handlers of the :signal:`response_downloaded` signal. .. attribute:: Response.meta A shortcut to the :attr:`Request.meta` attribute of the :attr:`Response.request` object (ie. ``self.request.meta``). Unlike the :attr:`Response.request` attribute, the :attr:`Response.meta` attribute is propagated along redirects and retries, so you will get the original :attr:`Request.meta` sent from your spider. .. seealso:: :attr:`Request.meta` attribute .. attribute:: Response.flags A list that contains flags for this response. Flags are labels used for tagging Responses. For example: `'cached'`, `'redirected`', etc. And they're shown on the string representation of the Response (`__str__` method) which is used by the engine for logging. .. method:: Response.copy() Returns a new Response which is a copy of this Response. .. method:: Response.replace([url, status, headers, body, request, flags, cls]) Returns a Response object with the same members, except for those members given new values by whichever keyword arguments are specified. The attribute :attr:`Response.meta` is copied by default. .. method:: Response.urljoin(url) Constructs an absolute url by combining the Response's :attr:`url` with a possible relative url. This is a wrapper over `urlparse.urljoin`_, it's merely an alias for making this call:: urlparse.urljoin(response.url, url) .. _urlparse.urljoin: https://docs.python.org/2/library/urlparse.html#urlparse.urljoin .. _topics-request-response-ref-response-subclasses: Response subclasses =================== Here is the list of available built-in Response subclasses. You can also subclass the Response class to implement your own functionality. TextResponse objects -------------------- .. class:: TextResponse(url, [encoding[, ...]]) :class:`TextResponse` objects adds encoding capabilities to the base :class:`Response` class, which is meant to be used only for binary data, such as images, sounds or any media file. :class:`TextResponse` objects support a new constructor argument, in addition to the base :class:`Response` objects. The remaining functionality is the same as for the :class:`Response` class and is not documented here. :param encoding: is a string which contains the encoding to use for this response. If you create a :class:`TextResponse` object with a unicode body, it will be encoded using this encoding (remember the body attribute is always a string). If ``encoding`` is ``None`` (default value), the encoding will be looked up in the response headers and body instead. :type encoding: string :class:`TextResponse` objects support the following attributes in addition to the standard :class:`Response` ones: .. attribute:: TextResponse.encoding A string with the encoding of this response. The encoding is resolved by trying the following mechanisms, in order: 1. the encoding passed in the constructor `encoding` argument 2. the encoding declared in the Content-Type HTTP header. If this encoding is not valid (ie. unknown), it is ignored and the next resolution mechanism is tried. 3. the encoding declared in the response body. The TextResponse class doesn't provide any special functionality for this. However, the :class:`HtmlResponse` and :class:`XmlResponse` classes do. 4. the encoding inferred by looking at the response body. This is the more fragile method but also the last one tried. .. attribute:: TextResponse.selector A :class:`~scrapy.selector.Selector` instance using the response as target. The selector is lazily instantiated on first access. :class:`TextResponse` objects support the following methods in addition to the standard :class:`Response` ones: .. method:: TextResponse.body_as_unicode() Returns the body of the response as unicode. This is equivalent to:: response.body.decode(response.encoding) But **not** equivalent to:: unicode(response.body) Since, in the latter case, you would be using the system default encoding (typically `ascii`) to convert the body to unicode, instead of the response encoding. .. method:: TextResponse.xpath(query) A shortcut to ``TextResponse.selector.xpath(query)``:: response.xpath('//p') .. method:: TextResponse.css(query) A shortcut to ``TextResponse.selector.css(query)``:: response.css('p') HtmlResponse objects -------------------- .. class:: HtmlResponse(url[, ...]) The :class:`HtmlResponse` class is a subclass of :class:`TextResponse` which adds encoding auto-discovering support by looking into the HTML `meta http-equiv`_ attribute. See :attr:`TextResponse.encoding`. .. _meta http-equiv: http://www.w3schools.com/TAGS/att_meta_http_equiv.asp XmlResponse objects ------------------- .. class:: XmlResponse(url[, ...]) The :class:`XmlResponse` class is a subclass of :class:`TextResponse` which adds encoding auto-discovering support by looking into the XML declaration line. See :attr:`TextResponse.encoding`. .. _Twisted Failure: http://twistedmatrix.com/documents/current/api/twisted.python.failure.Failure.html