Appendix G: Request and Respon

Django uses request and response objects to pass state through the system.

When a page is requested, Django creates an HttpRequest object that contains metadata about the request. Then Django loads the appropriate view, passing the HttpRequest as the first argument to the view function. Each view is responsible for returning an HttpResponse object.

This document explains the APIs for HttpRequest and HttpResponse objects, which are defined in thedjango.http module.

HttpRequest objects

class HttpRequest

Attributes

All attributes should be considered read-only, unless stated otherwise below. session is a notable exception.

HttpRequest.scheme

A string representing the scheme of the request (http or https usually).

HttpRequest.body

The raw HTTP request body as a byte string. This is useful for processing data in different ways than conventional HTML forms: binary images, XML payload etc. For processing conventional form data, useHttpRequest.POST.

You can also read from an HttpRequest using a file-like interface. See HttpRequest.read().

HttpRequest.path

A string representing the full path to the requested page, not including the domain.

Example: "/music/bands/the_beatles/"

HttpRequest.path_info

Under some Web server configurations, the portion of the URL after the host name is split up into a script prefix portion and a path info portion. The path_info attribute always contains the path info portion of the path, no matter what Web server is being used. Using this instead of path can make your code easier to move between test and deployment servers.

For example, if the WSGIScriptAlias for your application is set to "/minfo", then path might be"/minfo/music/bands/the_beatles/" and path_info would be "/music/bands/the_beatles/".

HttpRequest.method

A string representing the HTTP method used in the request. This is guaranteed to be uppercase. Example:

if request.method == "GET":
    do_something()
elif request.method == "POST":
    do_something_else()

HttpRequest.encoding

A string representing the current encoding used to decode form submission data (or None, which means the DEFAULT_CHARSET setting is used). You can write to this attribute to change the encoding used when accessing the form data. Any subsequent attribute accesses (such as reading from GET or POST) will use the new encoding value. Useful if you know the form data is not in the DEFAULT_CHARSET encoding.

HttpRequest.GET

A dictionary-like object containing all given HTTP GET parameters. See the QueryDict documentation below.

HttpRequest.POST

A dictionary-like object containing all given HTTP POST parameters, providing that the request contains form data. See the QueryDict documentation below. If you need to access raw or non-form data posted in the request, access this through the HttpRequest.body attribute instead.

Its possible that a request can come in via POST with an empty POST dictionary if, say, a form is requested via the POST HTTP method but does not include form data. Therefore, you shouldnt use if request.POST to check for use of the POST method; instead, use if request.method == "POST" (see above).

Note: POST does not include file-upload information. See FILES.

HttpRequest.COOKIES

A standard Python dictionary containing all cookies. Keys and values are strings.

HttpRequest.FILES

A dictionary-like object containing all uploaded files. Each key in FILES is the name from the <inputtype="file" name="" />. Each value in FILES is an UploadedFile.

Note that FILES will only contain data if the request method was POST and the <form> that posted to the request had enctype="multipart/form-data". Otherwise, FILES will be a blank dictionary-like object.

HttpRequest.META

A standard Python dictionary containing all available HTTP headers. Available headers depend on the client and server, but here are some examples:

• CONTENT_LENGTH  the length of the request body (as a string).
• CONTENT_TYPE  the MIME type of the request body.
• HTTP_ACCEPT_ENCODING  Acceptable encodings for the response.
• HTTP_ACCEPT_LANGUAGE  Acceptable languages for the response.
• HTTP_HOST  The HTTP Host header sent by the client.
• HTTP_REFERER  The referring page, if any.
• HTTP_USER_AGENT  The clients user-agent string.
• QUERY_STRING  The query string, as a single (unparsed) string.
• REMOTE_ADDR  The IP address of the client.
• REMOTE_HOST  The hostname of the client.
• REMOTE_USER  The user authenticated by the Web server, if any.
• REQUEST_METHOD  A string such as "GET" or "POST".
• SERVER_NAME  The hostname of the server.
• SERVER_PORT  The port of the server (as a string).

With the exception of CONTENT_LENGTH and CONTENT_TYPE, as given above, any HTTP headers in the request are converted to META keys by converting all characters to uppercase, replacing any hyphens with underscores and adding an HTTP_ prefix to the name. So, for example, a header called X-Bender would be mapped to theMETA key HTTP_X_BENDER.

HttpRequest.user

An object of type AUTH_USER_MODEL representing the currently logged-in user. If the user isnt currently logged in, user will be set to an instance of django.contrib.auth.models.AnonymousUser. You can tell them apart with is_authenticated(), like so:

if request.user.is_authenticated():
    # Do something for logged-in users.
else:
    # Do something for anonymous users.

user is only available if your Django installation has the AuthenticationMiddleware activated.

HttpRequest.session

A readable-and-writable, dictionary-like object that represents the current session. This is only available if your Django installation has session support activated.

HttpRequest.urlconf

Not defined by Django itself, but will be read if other code (e.g., a custom middleware class) sets it. When present, this will be used as the root URLconf for the current request, overriding the ROOT_URLCONF setting. See how-django-processes-a-request for details.

HttpRequest.resolver_match

An instance of ResolverMatch representing the resolved url. This attribute is only set after url resolving took place, which means its available in all views but not in middleware methods which are executed before url resolving takes place (like process_request, you can use process_view instead).

Methods

HttpRequest.get_host()

Returns the originating host of the request using information from the HTTP_X_FORWARDED_HOST (ifUSE_X_FORWARDED_HOST is enabled) and HTTP_HOST headers, in that order. If they dont provide a value, the method uses a combination of SERVER_NAME and SERVER_PORT as detailed in PEP 3333.

Example: "127.0.0.1:8000"

Note

The get_host() method fails when the host is behind multiple proxies. One solution is to use middleware to rewrite the proxy headers, as in the following example:

class MultipleProxyMiddleware(object):
    FORWARDED_FOR_FIELDS = [
        "HTTP_X_FORWARDED_FOR",
        "HTTP_X_FORWARDED_HOST",
        "HTTP_X_FORWARDED_SERVER",
    ]

    def process_request(self, request):
        """
        Rewrites the proxy headers so that only the most
        recent proxy is used.
        """
        for field in self.FORWARDED_FOR_FIELDS:
            if field in request.META:
                if "," in request.META[field]:
                    parts = request.META[field].split(",")
                    request.META[field] = parts[-1].strip()

This middleware should be positioned before any other middleware that relies on the value of get_host()  for instance, CommonMiddleware or CsrfViewMiddleware.

HttpRequest.get_full_path()

Returns the path, plus an appended query string, if applicable.

Example: "/music/bands/the_beatles/?print=true"

HttpRequest.build_absolute_uri(location)

Returns the absolute URI form of location. If no location is provided, the location will be set torequest.get_full_path().

If the location is already an absolute URI, it will not be altered. Otherwise the absolute URI is built using the server variables available in this request.

Example: "http://example.com/music/bands/the_beatles/?print=true"

HttpRequest.get_signed_cookie(key, default=RAISE_ERROR, salt=”, max_age=None)

Returns a cookie value for a signed cookie, or raises a django.core.signing.BadSignature exception if the signature is no longer valid. If you provide the default argument the exception will be suppressed and that default value will be returned instead.

The optional salt argument can be used to provide extra protection against brute force attacks on your secret key. If supplied, the max_age argument will be checked against the signed timestamp attached to the cookie value to ensure the cookie is not older than max_age seconds.

For example:

>>> request.get_signed_cookie("name")
"Tony"
>>> request.get_signed_cookie("name", salt="name-salt")
"Tony" # assuming cookie was set using the same salt
>>> request.get_signed_cookie("non-existing-cookie")
...
KeyError: "non-existing-cookie"
>>> request.get_signed_cookie("non-existing-cookie", False)
False
>>> request.get_signed_cookie("cookie-that-was-tampered-with")
...
BadSignature: ...
>>> request.get_signed_cookie("name", max_age=60)
...
SignatureExpired: Signature age 1677.3839159 > 60 seconds
>>> request.get_signed_cookie("name", False, max_age=60)
False

See cryptographic signing for more information.

HttpRequest.is_secure()

Returns True if the request is secure; that is, if it was made with HTTPS.

HttpRequest.is_ajax()

Returns True if the request was made via an XMLHttpRequest, by checking the HTTP_X_REQUESTED_WITH header for the string "XMLHttpRequest". Most modern JavaScript libraries send this header. If you write your own XMLHttpRequest call (on the browser side), youll have to set this header manually if you want is_ajax() to work.

If a response varies on whether or not its requested via AJAX and you are using some form of caching like Djangos cache middleware, you should decorate the view with vary_on_headers("HTTP_X_REQUESTED_WITH") so that the responses are properly cached.

HttpRequest.read(size=None)

HttpRequest.readline()

HttpRequest.readlines()

HttpRequest.xreadlines()

HttpRequest.__iter__()

Methods implementing a file-like interface for reading from an HttpRequest instance. This makes it possible to consume an incoming request in a streaming fashion. A common use-case would be to process a big XML payload with iterative parser without constructing a whole XML tree in memory.

Given this standard interface, an HttpRequest instance can be passed directly to an XML parser such as ElementTree:

import xml.etree.ElementTree as ET
for element in ET.iterparse(request):
    process(element)

QueryDict objects

class QueryDict

In an HttpRequest object, the GET and POST attributes are instances of django.http.QueryDict, a dictionary-like class customized to deal with multiple values for the same key. This is necessary because some HTML form elements, notably <select multiple>, pass multiple values for the same key.

The QueryDicts at request.POST and request.GET will be immutable when accessed in a normal request/response cycle. To get a mutable version you need to use .copy().

Methods

QueryDict implements all the standard dictionary methods because its a subclass of dictionary. Exceptions are outlined here:

QueryDict.__init__(query_string=None, mutable=False, encoding=None)

Instantiates a QueryDict object based on query_string.

>>> QueryDict("a=1&a=2&c=3")
<QueryDict: {"a": ["1", "2"], "c": ["3"]}>

If query_string is not passed in, the resulting QueryDict will be empty (it will have no keys or values).

Most QueryDicts you encounter, and in particular those at request.POST and request.GET, will be immutable. If you are instantiating one yourself, you can make it mutable by passing mutable=True to its __init__().

Strings for setting both keys and values will be converted from encoding to unicode. If encoding is not set, it defaults to DEFAULT_CHARSET.

Changed in version 1.8: In previous versions, query_string was a required positional argument.

QueryDict.__getitem__(key)

Returns the value for the given key. If the key has more than one value, __getitem__() returns the last value. Raises django.utils.datastructures.MultiValueDictKeyError if the key does not exist. (This is a subclass of Pythons standard KeyError, so you can stick to catching KeyError.)

QueryDict.__setitem__(key, value)

Sets the given key to [value] (a Python list whose single element is value). Note that this, as other dictionary functions that have side effects, can only be called on a mutable QueryDict (such as one that was created via copy()).

QueryDict.__contains__(key)

Returns True if the given key is set. This lets you do, e.g., if "foo" in request.GET.

QueryDict.get(key, default)

Uses the same logic as __getitem__() above, with a hook for returning a default value if the key doesnt exist.

QueryDict.setdefault(key, default)

Just like the standard dictionary setdefault() method, except it uses __setitem__() internally.

QueryDict.update(other_dict)

Takes either a QueryDict or standard dictionary. Just like the standard dictionary update() method, except itappends to the current dictionary items rather than replacing them. For example:

>>> q = QueryDict("a=1", mutable=True)
>>> q.update({"a": "2"})
>>> q.getlist("a")
["1", "2"]
>>> q["a"] # returns the last
["2"]

QueryDict.items()

Just like the standard dictionary items() method, except this uses the same last-value logic as__getitem__(). For example:

>>> q = QueryDict("a=1&a=2&a=3")
>>> q.items()
[("a", "3")]

QueryDict.iteritems()

Just like the standard dictionary iteritems() method. Like QueryDict.items() this uses the same last-value logic as QueryDict.__getitem__().

QueryDict.iterlists()

Like QueryDict.iteritems() except it includes all values, as a list, for each member of the dictionary.

QueryDict.values()

Just like the standard dictionary values() method, except this uses the same last-value logic as__getitem__(). For example:

>>> q = QueryDict("a=1&a=2&a=3")
>>> q.values()
["3"]

QueryDict.itervalues()

Just like QueryDict.values(), except an iterator.

In addition, QueryDict has the following methods:

QueryDict.copy()

Returns a copy of the object, using copy.deepcopy() from the Python standard library. This copy will be mutable even if the original was not.

QueryDict.getlist(key, default)

Returns the data with the requested key, as a Python list. Returns an empty list if the key doesnt exist and no default value was provided. Its guaranteed to return a list of some sort unless the default value was no list.

QueryDict.setlist(key, list_)

Sets the given key to list_ (unlike __setitem__()).

QueryDict.appendlist(key, item)

Appends an item to the internal list associated with key.

QueryDict.setlistdefault(key, default_list)

Just like setdefault, except it takes a list of values instead of a single value.

QueryDict.lists()

Like items(), except it includes all values, as a list, for each member of the dictionary. For example:

>>> q = QueryDict("a=1&a=2&a=3")
>>> q.lists()
[("a", ["1", "2", "3"])]

QueryDict.pop(key)

Returns a list of values for the given key and removes them from the dictionary. Raises KeyError if the key does not exist. For example:

>>> q = QueryDict("a=1&a=2&a=3", mutable=True)
>>> q.pop("a")
["1", "2", "3"]

QueryDict.popitem()

Removes an arbitrary member of the dictionary (since theres no concept of ordering), and returns a two value tuple containing the key and a list of all values for the key. Raises KeyError when called on an empty dictionary. For example:

>>> q = QueryDict("a=1&a=2&a=3", mutable=True)
>>> q.popitem()
("a", ["1", "2", "3"])

QueryDict.dict()

Returns dict representation of QueryDict. For every (key, list) pair in QueryDict, dict will have (key, item), where item is one element of the list, using same logic as QueryDict.__getitem__():

>>> q = QueryDict("a=1&a=3&a=5")
>>> q.dict()
{"a": "5"}

QueryDict.urlencode([*safe*])

Returns a string of the data in query-string format. Example:

>>> q = QueryDict("a=2&b=3&b=5")
>>> q.urlencode()
"a=2&b=3&b=5"

Optionally, urlencode can be passed characters which do not require encoding. For example:

>>> q = QueryDict(mutable=True)
>>> q["next"] = "/a&b/"
>>> q.urlencode(safe="/")
"next=/a%26b/"

HttpResponse objects

class HttpResponse

In contrast to HttpRequest objects, which are created automatically by Django, HttpResponse objects are your responsibility. Each view you write is responsible for instantiating, populating and returning anHttpResponse.

The HttpResponse class lives in the django.http module.

Usage

PASSING STRINGS

Typical usage is to pass the contents of the page, as a string, to the HttpResponse constructor:

>>> from django.http import HttpResponse
>>> response = HttpResponse("Here"s the text of the Web page.")
>>> response = HttpResponse("Text only, please.", content_type="text/plain")

But if you want to add content incrementally, you can use response as a file-like object:

>>> response = HttpResponse()
>>> response.write("<p>Here"s the text of the Web page.</p>")
>>> response.write("<p>Here"s another paragraph.</p>")

PASSING ITERATORS

Finally, you can pass HttpResponse an iterator rather than strings. HttpResponse will consume the iterator immediately, store its content as a string, and discard it.

If you need the response to be streamed from the iterator to the client, you must use theStreamingHttpResponse class instead.

SETTING HEADER FIELDS

To set or remove a header field in your response, treat it like a dictionary:

>>> response = HttpResponse()
>>> response["Age"] = 120
>>> del response["Age"]

Note that unlike a dictionary, del doesnt raise KeyError if the header field doesnt exist.

For setting the Cache-Control and Vary header fields, it is recommended to use the patch_cache_control() andpatch_vary_headers() methods from django.utils.cache, since these fields can have multiple, comma-separated values. The patch methods ensure that other values, e.g. added by a middleware, are not removed.

HTTP header fields cannot contain newlines. An attempt to set a header field containing a newline character (CR or LF) will raise BadHeaderError

TELLING THE BROWSER TO TREAT THE RESPONSE AS A FILE ATTACHMENT

To tell the browser to treat the response as a file attachment, use the content_type argument and set theContent-Disposition header. For example, this is how you might return a Microsoft Excel spreadsheet:

>>> response = HttpResponse(my_data, content_type="application/vnd.ms-excel")
>>> response["Content-Disposition"] = "attachment; filename="foo.xls""

Theres nothing Django-specific about the Content-Disposition header, but its easy to forget the syntax, so weve included it here.

Attributes

HttpResponse.content

A bytestring representing the content, encoded from a Unicode object if necessary.

HttpResponse.charset

A string denoting the charset in which the response will be encoded. If not given at HttpResponseinstantiation time, it will be extracted from content_type and if that is unsuccessful, the DEFAULT_CHARSETsetting will be used.

HttpResponse.status_code

The HTTP status code for the response.

HttpResponse.reason_phrase

The HTTP reason phrase for the response.

HttpResponse.streaming

This is always False.

This attribute exists so middleware can treat streaming responses differently from regular responses.

HttpResponse.closed

True if the response has been closed.

Methods

HttpResponse.__init__(content=”, content_type=None, status=200, reason=None, charset=None)

Instantiates an HttpResponse object with the given page content and content type.

content should be an iterator or a string. If its an iterator, it should return strings, and those strings will be joined together to form the content of the response. If it is not an iterator or a string, it will be converted to a string when accessed.

content_type is the MIME type optionally completed by a character set encoding and is used to fill the HTTP Content-Type header. If not specified, it is formed by the DEFAULT_CONTENT_TYPE and DEFAULT_CHARSETsettings, by default: text/html; charset=utf-8.

status is the HTTP status code for the response.

reason is the HTTP response phrase. If not provided, a default phrase will be used.

charset is the charset in which the response will be encoded. If not given it will be extracted fromcontent_type, and if that is unsuccessful, the DEFAULT_CHARSET setting will be used.

HttpResponse.__setitem__(header, value)

Sets the given header name to the given value. Both header and value should be strings.

HttpResponse.__delitem__(header)

Deletes the header with the given name. Fails silently if the header doesnt exist. Case-insensitive.

HttpResponse.__getitem__(header)

Returns the value for the given header name. Case-insensitive.

HttpResponse.has_header(header)

Returns True or False based on a case-insensitive check for a header with the given name.

HttpResponse.setdefault(header, value)

Sets a header unless it has already been set.

HttpResponse.set_cookie(key, value=”, max_age=None, expires=None, path=’/’, domain=None, secure=None,httponly=False)

Sets a cookie. The parameters are the same as in the Morsel cookie object in the Python standard library.

• max_age should be a number of seconds, or None (default) if the cookie should last only as long as the clients browser session. If expires is not specified, it will be calculated.

• expires should either be a string in the format "Wdy, DD-Mon-YY HH:MM:SS GMT" or a datetime.datetime object in UTC. If expires is a datetime object, the max_age will be calculated.

• Use domain if you want to set a cross-domain cookie. For example, domain=".lawrence.com" will set a cookie that is readable by the domains www.lawrence.com, blogs.lawrence.com and calendars.lawrence.com. Otherwise, a cookie will only be readable by the domain that set it.

• Use httponly=True if you want to prevent client-side JavaScript from having access to the cookie.

  HTTPOnly is a flag included in a Set-Cookie HTTP response header. It is not part of the RFC 2109 standard for cookies, and it isnt honored consistently by all browsers. However, when it is honored, it can be a useful way to mitigate the risk of client side script accessing the protected cookie data.

Warning

Both RFC 2109 and RFC 6265 state that user agents should support cookies of at least 4096 bytes. For many browsers this is also the maximum size. Django will not raise an exception if theres an attempt to store a cookie of more than 4096 bytes, but many browsers will not set the cookie correctly.

HttpResponse.set_signed_cookie(key, value, salt=”, max_age=None, expires=None, path=’/’, domain=None,secure=None, httponly=True)

Like set_cookie(), but cryptographic signing the cookie before setting it. Use in conjunction withHttpRequest.get_signed_cookie(). You can use the optional salt argument for added key strength, but you will need to remember to pass it to the corresponding HttpRequest.get_signed_cookie() call.

HttpResponse.delete_cookie(key, path=’/’, domain=None)

Deletes the cookie with the given key. Fails silently if the key doesnt exist.

Due to the way cookies work, path and domain should be the same values you used in set_cookie()  otherwise the cookie may not be deleted.

HttpResponse.write(content)

This method makes an HttpResponse instance a file-like object.

HttpResponse.flush()

This method makes an HttpResponse instance a file-like object.

HttpResponse.tell()

This method makes an HttpResponse instance a file-like object.

HttpResponse.getvalue()

Returns the value of HttpResponse.content. This method makes an HttpResponse instance a stream-like object.

HttpResponse.writable()

Always True. This method makes an HttpResponse instance a stream-like object.

HttpResponse.writelines(lines)

Writes a list of lines to the response. Line separators are not added. This method makes an HttpResponseinstance a stream-like object.

HttpResponse subclasses

Django includes a number of HttpResponse subclasses that handle different types of HTTP responses. LikeHttpResponse, these subclasses live in django.http.

class HttpResponseRedirect

The first argument to the constructor is required the path to redirect to. This can be a fully qualified URL (e.g. "http://www.yahoo.com/search/") or an absolute path with no domain (e.g. "/search/"). See HttpResponsefor other optional constructor arguments. Note that this returns an HTTP status code 302.

url

This read-only attribute represents the URL the response will redirect to (equivalent to the Locationresponse header).

class HttpResponsePermanentRedirect

Like HttpResponseRedirect, but it returns a permanent redirect (HTTP status code 301) instead of a found redirect (status code 302).

class HttpResponseNotModified

The constructor doesnt take any arguments and no content should be added to this response. Use this to designate that a page hasnt been modified since the users last request (status code 304).

class HttpResponseBadRequest

Acts just like HttpResponse but uses a 400 status code.

class HttpResponseNotFound

Acts just like HttpResponse but uses a 404 status code.

class HttpResponseForbidden

Acts just like HttpResponse but uses a 403 status code.

class HttpResponseNotAllowed

Like HttpResponse, but uses a 405 status code. The first argument to the constructor is required: a list of permitted methods (e.g. ["GET", "POST"]).

class HttpResponseGone

Acts just like HttpResponse but uses a 410 status code.

class HttpResponseServerError

Acts just like HttpResponse but uses a 500 status code.

Note

If a custom subclass of HttpResponse implements a render method, Django will treat it as emulating aSimpleTemplateResponse, and the render method must itself return a valid response object.

JsonResponse objects

class JsonResponse

JsonResponse.__init__(data, encoder=DjangoJSONEncoder, safe=True, **kwargs)

An HttpResponse subclass that helps to create a JSON-encoded response. It inherits most behavior from its superclass with a couple differences:

Its default Content-Type header is set to application/json.

The first parameter, data, should be a dict instance. If the safe parameter is set to False (see below) it can be any JSON-serializable object.

The encoder, which defaults to django.core.serializers.json.DjangoJSONEncoder, will be used to serialize the data.

The safe boolean parameter defaults to True. If its set to False, any object can be passed for serialization (otherwise only dict instances are allowed). If safe is True and a non-dict object is passed as the first argument, a TypeError will be raised.

Usage

Typical usage could look like:

>>> from django.http import JsonResponse
>>> response = JsonResponse({"foo": "bar"})
>>> response.content
"{"foo": "bar"}"

SERIALIZING NON-DICTIONARY OBJECTS

In order to serialize objects other than dict you must set the safe parameter to False:

>>> response = JsonResponse([1, 2, 3], safe=False)

Without passing safe=False, a TypeError will be raised.

Warning

Before the 5th edition of EcmaScript it was possible to poison the JavaScript Array constructor. For this reason, Django does not allow passing non-dict objects to the JsonResponse constructor by default. However, most modern browsers implement EcmaScript 5 which removes this attack vector. Therefore it is possible to disable this security precaution.

CHANGING THE DEFAULT JSON ENCODER

If you need to use a different JSON encoder class you can pass the encoder parameter to the constructor method:

>>> response = JsonResponse(data, encoder=MyJSONEncoder)

StreamingHttpResponse objects

class StreamingHttpResponse

The StreamingHttpResponse class is used to stream a response from Django to the browser. You might want to do this if generating the response takes too long or uses too much memory. For instance, its useful for generating large CSV files .

Performance considerations

Django is designed for short-lived requests. Streaming responses will tie a worker process for the entire duration of the response. This may result in poor performance.

Generally speaking, you should perform expensive tasks outside of the request-response cycle, rather than resorting to a streamed response.

The StreamingHttpResponse is not a subclass of HttpResponse, because it features a slightly different API. However, it is almost identical, with the following notable differences:

• It should be given an iterator that yields strings as content.
• You cannot access its content, except by iterating the response object itself. This should only occur when the response is returned to the client.
• It has no content attribute. Instead, it has a streaming_content attribute.
• You cannot use the file-like object tell() or write() methods. Doing so will raise an exception.

StreamingHttpResponse should only be used in situations where it is absolutely required that the whole content isnt iterated before transferring the data to the client. Because the content cant be accessed, many middlewares cant function normally. For example the ETag and Content- Length headers cant be generated for streaming responses.

Attributes

StreamingHttpResponse.streaming_content

An iterator of strings representing the content.

StreamingHttpResponse.status_code

The HTTP status code for the response.

StreamingHttpResponse.reason_phrase

The HTTP reason phrase for the response.

StreamingHttpResponse.streaming

This is always True.

FileResponse objects

class FileResponse

FileResponse is a subclass of StreamingHttpResponse optimized for binary files. It uses wsgi.file_wrapper if provided by the wsgi server, otherwise it streams the file out in small chunks.

FileResponse expects a file open in binary mode like so:

>>> from django.http import FileResponse
>>> response = FileResponse(open("myfile.png", "rb"))

Error views

Django comes with a few views by default for handling HTTP errors. To override these with your own custom views, see customizing-error-views.

The 404 (page not found) view

defaults.page_not_found(request, template_name=’404.html’)

When you raise Http404 from within a view, Django loads a special view devoted to handling 404 errors. By default, its the view django.views.defaults.page_not_found(), which either produces a very simple Not Found message or loads and renders the template 404.html if you created it in your root template directory.

The default 404 view will pass one variable to the template: request_path, which is the URL that resulted in the error.

Three things to note about 404 views:

• The 404 view is also called if Django doesnt find a match after checking every regular expression in the URLconf.
• The 404 view is passed a RequestContext and will have access to variables supplied by your template context processors (e.g. MEDIA_URL).
• If DEBUG is set to True (in your settings module), then your 404 view will never be used, and your URLconf will be displayed instead, with some debug information.

The 500 (server error) view

defaults.server_error(request, template_name=’500.html’)

Similarly, Django executes special-case behavior in the case of runtime errors in view code. If a view results in an exception, Django will, by default, call the view django.views.defaults.server_error, which either produces a very simple Server Error message or loads and renders the template 500.html if you created it in your root template directory.

The default 500 view passes no variables to the 500.html template and is rendered with an empty Context to lessen the chance of additional errors.

If DEBUG is set to True (in your settings module), then your 500 view will never be used, and the traceback will be displayed instead, with some debug information.

The 403 (HTTP Forbidden) view

defaults.permission_denied(request, template_name=’403.html’)

In the same vein as the 404 and 500 views, Django has a view to handle 403 Forbidden errors. If a view results in a 403 exception then Django will, by default, call the viewdjango.views.defaults.permission_denied.

This view loads and renders the template 403.html in your root template directory, or if this file does not exist, instead serves the text 403 Forbidden, as per RFC 2616 (the HTTP 1.1 Specification).

django.views.defaults.permission_denied is triggered by a PermissionDenied exception. To deny access in a view you can use code like this:

from django.core.exceptions import PermissionDenied

def edit(request, pk):
    if not request.user.is_staff:
        raise PermissionDenied
    # ...

The 400 (bad request) view

defaults.bad_request(request, template_name=’400.html’)

When a SuspiciousOperation is raised in Django, it may be handled by a component of Django (for example resetting the session data). If not specifically handled, Django will consider the current request a bad request instead of a server error.

django.views.defaults.bad_request, is otherwise very similar to the server_error view, but returns with the status code 400 indicating that the error condition was the result of a client operation.

bad_request views are also only used when DEBUG is False.

Customizing error views

The default error views in Django should suffice for most Web applications, but can easily be overridden if you need any custom behavior. Simply specify the handlers as seen below in your URLconf (setting them anywhere else will have no effect).

The page_not_found() view is overridden by handler404:

handler404 = "mysite.views.my_custom_page_not_found_view"

The server_error() view is overridden by handler500:

handler500 = "mysite.views.my_custom_error_view"

The permission_denied() view is overridden by handler403:

handler403 = "mysite.views.my_custom_permission_denied_view"

The bad_request() view is overridden by handler400:

handler400 = "mysite.views.my_custom_bad_request_view"