Requests and Responses¶
Scrapy uses Request
and Response
objects for crawling web
sites.
Typically, Request
objects are generated in the spiders and pass
across the system until they reach the Downloader, which executes the request
and returns a Response
object which travels back to the spider that
issued the request.
Both Request
and Response
classes have subclasses which add
functionality not required in the base classes. These are described
below in Request subclasses and
Response subclasses.
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 aResponse
.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 tostr
using the encoding passed (which defaults toutf-8
). Ifbody
is not given, an empty string is stored. Regardless of the type of this argument, the final value stored will be astr
(neverunicode
orNone
). - 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
andpath
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 theRequest.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.
- Using a dict:
- 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 tostr
(if given asunicode
). - 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()
orreplace()
methods, and can also be accessed, in your spider, from theresponse.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 themeta
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
(seecookies
parameter ofRequest
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 theRequest
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 standardRequest
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 defaultfrom_response()
behaviour may not be the most appropriate. To disable this behaviour you can set thedont_click
argument toTrue
. Also, if you want to change the control clicked (instead of disabling it) you can also use theclickdata
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.- response (
-
classmethod
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, body, flags])¶ 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
- 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
¶ 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 inTextResponse
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 theResponse.request
object (ie.self.request.meta
).Unlike the
Response.request
attribute, theResponse.meta
attribute is propagated along redirects and retries, so you will get the originalRequest.meta
sent from your spider.See also
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.
-
urljoin
(url)¶ Constructs an absolute url by combining the Response’s
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)
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
scrapy.http.
TextResponse
(url[, encoding[, ...]])¶ TextResponse
objects adds encoding capabilities to the baseResponse
class, which is meant to be used only for binary data, such as images, sounds or any media file.TextResponse
objects support a new constructor argument, in addition to the baseResponse
objects. The remaining functionality is the same as for theResponse
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). Ifencoding
isNone
(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 standardResponse
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 accessresponse.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
andXmlResponse
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 standardResponse
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')
-
HtmlResponse objects¶
-
class
scrapy.http.
HtmlResponse
(url[, ...])¶ The
HtmlResponse
class is a subclass ofTextResponse
which adds encoding auto-discovering support by looking into the HTML meta http-equiv attribute. SeeTextResponse.encoding
.
XmlResponse objects¶
-
class
scrapy.http.
XmlResponse
(url[, ...])¶ The
XmlResponse
class is a subclass ofTextResponse
which adds encoding auto-discovering support by looking into the XML declaration line. SeeTextResponse.encoding
.