.. module:: scrapy.http :synopsis: Request and Response classes
Scrapy使用 :class:`Request` 和 :class:`Response` 对象爬取web站点。
一般来说，:class:`Request` 对象在spiders中被生成并且最终传递到 下载器(Downloader)，下载器对其进行处理并返回一个 :class:`Response` 对象， :class:`Response` 对象还会返回到生成request的spider中。
所有 :class:`Request` and :class:`Response` 的子类都会实现一些在基类中非必要的 功能。它们会在 :ref:`topics-request-response-ref-request-subclasses` 和 :ref:`topics-request-response-ref-response-subclasses` 两部分进行详细的说明。
一个 :class:`Request` 对象代表一个HTTP请求，一般来讲， HTTP请求是由Spider产生并被Downloader处理进而生成一个 :class:`Response`。
| param url: | 请求的URL |
|---|---|
| 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: | 此请求的HTTP方法。默认是 |
| type method: | string |
| param meta: | :attr:`Request.meta` 属性的初始值。 一旦此参数被设置， 通过参数传递的字典将会被浅拷贝。 |
| type meta: | dict |
| param body: | request体。如果传进的参数是 |
| type body: | str or unicode |
| param headers: | 请求头。字典值的类型可以是strings
(for single valued headers) 或是 lists (for multi-valued headers)。如果传进的值是
|
| type headers: | dict |
| param cookies: | 请求的cookies。可以被设置成如下两种形式。
The latter form allows for customizing the 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 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 |
| type encoding: | string |
| param priority: | the priority of this request (defaults to |
| 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 |
| 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.
.. 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`.
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.log("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
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`
dont_merge_cookies(seecookiesparameter of :class:`Request` constructor)- :reqmeta:`cookiejar`
- :reqmeta:`redirect_urls`
- :reqmeta:`bindaddress`
.. reqmeta:: bindaddress
The IP of the outgoing IP address to use for the performing the request.
Here is the list of built-in :class:`Request` subclasses. You can also subclass it to implement your own custom functionality.
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.
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)]
通常网站通过 <input type="hidden"> 实现对某些表单字段（如数据或是登录界面中的认证令牌等）的预填充。
使用Scrapy抓取网页时，如果想要预填充或重写像用户名、用户密码这些表单字段，
可以使用 :meth:`FormRequest.from_response` 方法实现。下面是使用这种方法的爬虫例子:
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.log("Login failed", level=log.ERROR)
return
# continue scraping with authenticated session...
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 <topics-request-response-ref-response-subclasses>`, 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 <topics-downloader-middleware>`.
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 <topics-spider-middleware>`, 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.
Here is the list of available built-in Response subclasses. You can also subclass the Response class to implement your own functionality.