Requests and Responses — Scrapy documentation
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
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. The following example shows how to achieve this by using the Request.cb_kwargs
attribute:
def parse(self, response):
request = scrapy.Request('http://www.example.com/index.html',
callback=self.parse_page2,
cb_kwargs=dict(main_url=response.url))
request.cb_kwargs['foo'] = 'bar' # add more arguments for the callback
yield request
def parse_page2(self, response, main_url, foo):
yield dict(
main_url=main_url,
other_url=response.url,
foo=foo,
)
Caution
Request.cb_kwargs
was introduced in version 1.7
. Prior to that, using Request.meta
was recommended for passing information around callbacks. After 1.7
, Request.cb_kwargs
became the preferred way for handling user information, leaving Request.meta
for communication with components like middlewares and extensions.
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 Failure
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
"https://example.invalid/", # 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)
Accessing additional data in errback functions
In case of a failure to process the request, you may be interested in accessing arguments to the callback functions so you can process further based on the arguments in the errback. The following example shows how to achieve this by using Failure.request.cb_kwargs
:
def parse(self, response):
request = scrapy.Request('http://www.example.com/index.html',
callback=self.parse_page2,
errback=self.errback_page2,
cb_kwargs=dict(main_url=response.url))
yield request
def parse_page2(self, response, main_url):
pass
def errback_page2(self, failure):
yield dict(
main_url=failure.request.cb_kwargs['main_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:
- :reqmeta:`bindaddress`
- :reqmeta:`cookiejar`
- :reqmeta:`dont_cache`
- :reqmeta:`dont_merge_cookies`
- :reqmeta:`dont_obey_robotstxt`
- :reqmeta:`dont_redirect`
- :reqmeta:`dont_retry`
- :reqmeta:`download_fail_on_dataloss`
- :reqmeta:`download_latency`
- :reqmeta:`download_maxsize`
- :reqmeta:`download_timeout`
ftp_password
(See :setting:`FTP_PASSWORD` for more info)ftp_user
(See :setting:`FTP_USER` for more info)- :reqmeta:`handle_httpstatus_all`
- :reqmeta:`handle_httpstatus_list`
- :reqmeta:`max_retry_times`
- :reqmeta:`proxy`
- :reqmeta:`redirect_reasons`
- :reqmeta:`redirect_urls`
- :reqmeta:`referrer_policy`
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: :setting:`DOWNLOAD_TIMEOUT`.
download_latency
The amount of time spent to fetch the response, since the request has been started, i.e. HTTP message sent over the network. This meta key only becomes available when the response has been downloaded. While most other meta keys are used to control Scrapy behavior, this one is supposed to be read-only.
download_fail_on_dataloss
Whether or not to fail on broken responses. See: :setting:`DOWNLOAD_FAIL_ON_DATALOSS`.
max_retry_times
The meta key is used set retry times per request. When initialized, the :reqmeta:`max_retry_times` meta key takes higher precedence over the :setting:`RETRY_TIMES` setting.
Stopping the download of a Response
Raising a StopDownload exception from a handler for the bytes_received or headers_received signals will stop the download of a given response. See the following example:
import scrapy
class StopSpider(scrapy.Spider):
name = "stop"
start_urls = ["https://docs.scrapy.org/en/latest/"]
@classmethod
def from_crawler(cls, crawler):
spider = super().from_crawler(crawler)
crawler.signals.connect(spider.on_bytes_received, signal=scrapy.signals.bytes_received)
return spider
def parse(self, response):
# 'last_chars' show that the full response was not downloaded
yield {"len": len(response.text), "last_chars": response.text[-40:]}
def on_bytes_received(self, data, request, spider):
raise scrapy.exceptions.StopDownload(fail=False)
which produces the following output:
2020-05-19 17:26:12 [scrapy.core.engine] INFO: Spider opened
2020-05-19 17:26:12 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
2020-05-19 17:26:13 [scrapy.core.downloader.handlers.http11] DEBUG: Download stopped for <GET https://docs.scrapy.org/en/latest/> from signal handler StopSpider.on_bytes_received
2020-05-19 17:26:13 [scrapy.core.engine] DEBUG: Crawled (200) <GET https://docs.scrapy.org/en/latest/> (referer: None) ['download_stopped']
2020-05-19 17:26:13 [scrapy.core.scraper] DEBUG: Scraped from <200 https://docs.scrapy.org/en/latest/>
{'len': 279, 'last_chars': 'dth, initial-scale=1.0">\n \n <title>Scr'}
2020-05-19 17:26:13 [scrapy.core.engine] INFO: Closing spider (finished)
By default, resulting responses are handled by their corresponding errbacks. To call their callback instead, like in this example, pass fail=False
to the StopDownload exception.
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.request.form.FormRequest
- class scrapy.http.FormRequest
- class scrapy.FormRequest(url[, formdata, ...])
The
FormRequest
class adds a new keyword parameter to the__init__
method. The remaining arguments are the same as for theRequest
class and are not documented here.- Parameters
formdata (dict or collections.abc.Iterable) – 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 FormRequest.from_response(response[, formname=None, formid=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.Caution
Using this method with select elements which have leading or trailing whitespace in the option values will not work due to a bug in lxml, which should be fixed in lxml 3.8 and above.
- Parameters
response (
Response
object) – the response containing a HTML form which will be used to pre-populate the form fieldsformname (str) – if given, the form with name attribute set to this value will be used.
formid (str) – if given, the form with id attribute set to this value will be used.
formxpath (str) – if given, the first form that matches the xpath will be used.
formcss (str) – if given, the first form that matches the css selector will be used.
formnumber (int) – 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. If a value passed in this parameter isNone
, the field will not be included in the request, even if it was present in the response<form>
element.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 (bool) – 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
__init__
method.
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
def authentication_failed(response):
# TODO: Check the contents of the response and return True if it failed
# or False if it succeeded.
pass
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):
if authentication_failed(response):
self.logger.error("Login failed")
return
# continue scraping with authenticated session...
JsonRequest
The JsonRequest class extends the base Request
class with functionality for dealing with JSON requests.
- class scrapy.http.JsonRequest(url[, ... data, dumps_kwargs])
The JsonRequest class adds two new keyword parameters to the
__init__
method. The remaining arguments are the same as for theRequest
class and are not documented here.Using the JsonRequest will set the
Content-Type
header toapplication/json
andAccept
header toapplication/json, text/javascript, */*; q=0.01
- Parameters
data (object) – is any JSON serializable object that needs to be JSON encoded and assigned to body. if
Request.body
argument is provided this parameter will be ignored. ifRequest.body
argument is not provided and data argument is providedRequest.method
will be set to'POST'
automatically.dumps_kwargs (dict) – Parameters that will be passed to underlying
json.dumps()
method which is used to serialize data into JSON format.
JsonRequest usage example
Sending a JSON POST request with a JSON payload:
data = {
'name1': 'value1',
'name2': 'value2',
}
yield JsonRequest(url='http://www.example.com/post/action', data=data)
Response objects
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 base
Response
class, which is meant to be used only for binary data, such as images, sounds or any media file.TextResponse objects support a new
__init__
method argument, in addition to the baseResponse
objects. The remaining functionality is the same as for theResponse
class and is not documented here.- Parameters
encoding (str) – is a string which contains the encoding to use for this response. If you create a TextResponse object with a string as body, it will be converted to bytes encoded using this encoding. If encoding is
None
(default), 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 a string.
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
str(response.body)
is not a correct way to convert the response body into a string:>>> str(b'body') "b'body'"
- 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
__init__
methodencoding
argumentthe encoding declared in the Content-Type HTTP header. If this encoding is not valid (i.e. 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')
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.