Request和Response¶

Scrapy使用Request和Response对象爬取网站。

通常情况下，Request对象在Spider中生成并在系统中传递直至它们到达Downloader，Downloader执行Request并返回一个Response对象，然后Response对象再返回到生成Request的Spider中。

Request和Response类都有子类，这些子类添加了基类中没有要求的功能。这些子类在下面的Request子类和Response子类中讲述。

Request对象¶

class scrapy.http.Request(url[, callback, method='GET', headers, body, cookies, meta, encoding='utf-8', priority=0, dont_filter=False, errback])¶

A Request object represents an HTTP request, which is usually generated in the Spider and executed by the Downloader, and thus generating a Response.

Parameters:

url (string) – the URL of this request
callback (callable) – the function that will be called with the response of this request (once its downloaded) as its first parameter. For more information see Passing additional data to callback functions below. If a Request doesn’t specify a callback, the spider’s parse() method will be used. Note that if exceptions are raised during processing, errback is called instead.
method (string) – the HTTP method of this request. Defaults to 'GET'.
meta (dict) – the initial values for the Request.meta attribute. If given, the dict passed in this parameter will be shallow copied.
body (str or unicode) – 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).
headers (dict) – 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.

cookies (dict or list) –

the request cookies. These can be sent in two forms.

Using a dict:

request_with_cookies = Request(url="http://www.example.com",
                               cookies={'currency': 'USD', 'country': 'UY'})

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 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 CookiesMiddleware.

encoding (string) – 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).
priority (int) – 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.
dont_filter (boolean) – 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.
errback (callable) – 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. For more information, see Using errbacks to catch exceptions in request processing below.

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 replace().

method¶: A string representing the HTTP method in the request. This is guaranteed to be uppercase. Example: "GET", "POST", "PUT", etc

headers¶: A dictionary-like object which contains the request headers.

body¶

A str that contains the request body.

This attribute is read-only. To change the body of a Request use replace().

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 Request.meta special keys 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.

copy()¶: Return a new Request which is a copy of this Request. See also: Passing additional data to callback functions.

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 Request.meta is copied by default (unless a new value is given in the meta argument). See also Passing additional data to callback functions.

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 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 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

Using errbacks to catch exceptions in request processing¶

The errback of a request is a function that will be called when an exception is raise while processing it.

It receives a Twisted Failure instance as first parameter and can be used to track connection establishment timeouts, DNS errors etc.

Here’s an example spider logging all errors and catching some specific errors if needed:

import scrapy

from scrapy.spidermiddlewares.httperror import HttpError
from twisted.internet.error import DNSLookupError
from twisted.internet.error import TimeoutError, TCPTimedOutError

class ErrbackSpider(scrapy.Spider):
    name = "errback_example"
    start_urls = [
        "http://www.httpbin.org/",              # HTTP 200 expected
        "http://www.httpbin.org/status/404",    # Not found error
        "http://www.httpbin.org/status/500",    # server issue
        "http://www.httpbin.org:12345/",        # non-responding host, timeout expected
        "http://www.httphttpbinbin.org/",       # DNS error expected
    ]

    def start_requests(self):
        for u in self.start_urls:
            yield scrapy.Request(u, callback=self.parse_httpbin,
                                    errback=self.errback_httpbin,
                                    dont_filter=True)

    def parse_httpbin(self, response):
        self.logger.info('Got successful response from {}'.format(response.url))
        # do something useful here...

    def errback_httpbin(self, failure):
        # log all failures
        self.logger.error(repr(failure))

        # in case you want to do something special for some errors,
        # you may need the failure's type:

        if failure.check(HttpError):
            # these exceptions come from HttpError spider middleware
            # you can get the non-200 response
            response = failure.value.response
            self.logger.error('HttpError on %s', response.url)

        elif failure.check(DNSLookupError):
            # this is the original request
            request = failure.request
            self.logger.error('DNSLookupError on %s', request.url)

        elif failure.check(TimeoutError, TCPTimedOutError):
            request = failure.request
            self.logger.error('TimeoutError on %s', request.url)

Request.meta special keys¶

The Request.meta attribute can contain any arbitrary data, but there are some special keys recognized by Scrapy and its built-in extensions.

Those are:

dont_redirect
dont_retry
handle_httpstatus_list
handle_httpstatus_all
dont_merge_cookies (see cookies parameter of Request constructor)
cookiejar
dont_cache
redirect_urls
bindaddress
dont_obey_robotstxt
download_timeout
download_maxsize
proxy

bindaddress¶

The IP of the outgoing IP address to use for the performing the request.

download_timeout¶

The amount of time (in secs) that the downloader will wait before timing out. See also: DOWNLOAD_TIMEOUT.

Request subclasses¶

Here is the list of built-in Request subclasses. You can also subclass it to implement your own custom functionality.

FormRequest objects¶

The FormRequest class extends the base Request with functionality for dealing with HTML forms. It uses lxml.html forms to pre-populate form fields with form data from Response objects.

class scrapy.http.FormRequest(url[, formdata, ...])¶

The FormRequest class adds a new argument to the constructor. The remaining arguments are the same as for the Request class and are not documented here.

Parameters:	formdata (dict or iterable of tuples) – 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.

The FormRequest objects support the following class method in addition to the standard Request methods:

classmethod from_response(response[, formname=None, formnumber=0, formdata=None, formxpath=None, formcss=None, clickdata=None, dont_click=False, ...])¶

Returns a new FormRequest object with its form field values pre-populated with those found in the HTML <form> element contained in the given response. For an example see Using FormRequest.from_response() to simulate a user login.

The policy is to automatically simulate a click, by default, on any form control that looks clickable, like a <input type="submit">. 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 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.

Parameters:

response (Response object) – the response containing a HTML form which will be used to pre-populate the form fields
formname (string) – if given, the form with name attribute set to this value will be used.
formxpath (string) – if given, the first form that matches the xpath will be used.
formcss (string) – if given, the first form that matches the css selector will be used.
formnumber (integer) – the number of form to use, when the response contains multiple forms. The first one (and also the default) is 0.
formdata (dict) – fields to override in the form data. If a field was already present in the response <form> element, its value is overridden by the one passed in this parameter.
clickdata (dict) – 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.
dont_click (boolean) – If True, the form data will be submitted without clicking in any element.

The other parameters of this class method are passed directly to the FormRequest constructor.

New in version 0.10.3: The formname parameter.

New in version 0.17: The formxpath parameter.

New in version 1.1.0: The formcss 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 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)]

Using FormRequest.from_response() to simulate a user login¶

It is usual for web sites to provide pre-populated form fields through <input type="hidden"> 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 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 scrapy.http.Response(url[, status=200, headers=None, body=b'', flags=None, request=None])¶

A Response object represents an HTTP response, which is usually downloaded (by the Downloader) and fed to the Spiders for processing.

Parameters:

url (string) – the URL of this response
status (integer) – the HTTP status of the response. Defaults to 200.
headers (dict) – the headers of this response. The dict values can be strings (for single valued headers) or lists (for multi-valued headers).
body (str) – the response body. It must be str, not unicode, unless you’re using a encoding-aware Response subclass, such as TextResponse.
flags (list) – is a list containing the initial values for the Response.flags attribute. If given, the list will be shallow copied.
request (Request object) – the initial value of the Response.request attribute. This represents the Request that generated this response.

url¶

A string containing the URL of the response.

This attribute is read-only. To change the URL of a Response use replace().

status¶: An integer representing the HTTP status of the response. Example: 200, 404.

headers¶: A dictionary-like object which contains the response headers.

body¶

The body of this Response. Keep in mind that Response.body is always a bytes object. If you want the unicode version use TextResponse.text (only available in TextResponse and subclasses).

This attribute is read-only. To change the body of a Response use replace().

request¶

The Request object that generated this response. This attribute is assigned in the Scrapy engine, after the response and the request have passed through all 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 Spider Middlewares, but not in Downloader Middlewares (although you have the Request available there by other means) and handlers of the response_downloaded signal.

meta¶

A shortcut to the Request.meta attribute of the Response.request object (ie. self.request.meta).

Unlike the Response.request attribute, the Response.meta attribute is propagated along redirects and retries, so you will get the original Request.meta sent from your spider.

Response subclasses¶

以下是可用的内置Response子类列表。您还可以将Response类子类化以实现您自己的功能。

TextResponse objects¶

class scrapy.http.TextResponse(url[, encoding[, ...]])¶

TextResponse对象向基本Response类添加编码功能，这意味着仅用于二进制数据，例如图像，声音或任何媒体文件。

TextResponse objects support a new constructor argument, in addition to the base Response objects. The remaining functionality is the same as for the Response class and is not documented here.

Parameters:	encoding (string) – is a string which contains the encoding to use for this response. If you create a `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.

TextResponse objects support the following attributes in addition to the standard Response ones:

text¶

Response body, as unicode.

The same as response.body.decode(response.encoding), but the result is cached after the first call, so you can access response.text multiple times without extra overhead.

Note

unicode(response.body) is not a correct way to convert response body to unicode: you would be using the system default encoding (typically ascii) instead of the response encoding.

encoding¶

A string with the encoding of this response. The encoding is resolved by trying the following mechanisms, in order:

the encoding passed in the constructor encoding argument
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.
the encoding declared in the response body. The TextResponse class doesn’t provide any special functionality for this. However, the HtmlResponse and XmlResponse classes do.
the encoding inferred by looking at the response body. This is the more fragile method but also the last one tried.

selector¶: A Selector instance using the response as target. The selector is lazily instantiated on first access.

TextResponse objects support the following methods in addition to the standard Response ones:

xpath(query)¶

A shortcut to TextResponse.selector.xpath(query):

response.xpath('//p')

css(query)¶

A shortcut to TextResponse.selector.css(query):

response.css('p')

body_as_unicode()¶: The same as text, but available as a method. This method is kept for backwards compatibility; please prefer response.text.

HtmlResponse objects¶

class scrapy.http.HtmlResponse(url[, ...])¶: The HtmlResponse class is a subclass of TextResponse which adds encoding auto-discovering support by looking into the HTML meta http-equiv attribute. See TextResponse.encoding.

XmlResponse objects¶

class scrapy.http.XmlResponse(url[, ...])¶: The XmlResponse class is a subclass of TextResponse which adds encoding auto-discovering support by looking into the XML declaration line. See TextResponse.encoding.