请求和响应(Requests and Responses)

Request objects¶

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.

参数:

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 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.

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.

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)

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

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
• dont_merge_cookies (see cookies parameter of Request constructor)
• cookiejar
• redirect_urls
• bindaddress

Request subclasses¶

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

return [FormRequest(url="http://www.example.com/post/action",
                    formdata={'name': 'John Doe', 'age': '27'},
                    callback=self.after_post)]

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=scrapy.log.ERROR)
            return

        # continue scraping with authenticated session...

Response objects¶

class scrapy.http.Response(url[, status=200, headers, body, flags])¶

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

参数:

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

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¶

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 TextResponse.body_as_unicode() (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.

参见

Request.meta attribute

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.

copy()¶

Returns a new Response which is a copy of this 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 Response.meta is copied by default.

Response subclasses¶

Here is the list of available built-in Response subclasses. You can also subclass the Response class to implement your own functionality.