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====== Request and response objects ======
Created Friday 21 October 2011

===== Quick overview =====

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.

===== HttpRequest objects =====

==== class ====
 HttpRequest

==== Attributes ====

All attributes except **session** should be considered //read-only.//

**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** (this happens, for example, when using the **django.root** option with the modpython handler from Apache). 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 attr:~HttpRequest.path can make your code much easier to move between test and deployment servers.
			<Location "/mysite/">
			    SetHandler python-program
			    PythonHandler django.core.handlers.modpython
			    SetEnv DJANGO_SETTINGS_MODULE mysite.settings
			    PythonOption //django.root /mysite//
			    PythonDebug On
			</Location>
    For example, if the django.root 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. See the QueryDict documentation below.

    It's 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 shouldn't 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.REQUEST

    For convenience, a dictionary-like object that searches POST first, then GET. Inspired by PHP's $_REQUEST.

    For example, if GET = {"name": "john"} and POST = {"age": '34'}, REQUEST["name"] would be "john", and REQUEST["age"] would be "34".

    It's strongly suggested that you use GET and POST instead of REQUEST, because the former are more explicit.

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 <input type="file" name="" />. Each value in FILES is an UploadedFile as described below.

    See Managing files for more information.

    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 client's 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 the META key HTTP_X_BENDER.

HttpRequest.user

    A django.contrib.auth.models.User object representing the currently logged-in user. If the user isn't 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. For more, see User authentication in Django.

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. See the session documentation for full details.

HttpRequest.raw_post_data

    The raw HTTP POST data as a byte string. This is useful for processing data in different formats than of conventional HTML forms: binary images, XML payload etc. For processing form data use HttpRequest.POST.
    New in Django 1.3: Please, see the release notes

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

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.

Methods

HttpRequest.get_host()

    Returns the originating host of the request using information from the HTTP_X_FORWARDED_HOST (if enabled in the settings) and HTTP_HOST headers (in that order). If they don't 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()

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 to request.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)
    New in Django Development version.

    Returns a cookie value for a signed cookie, or raises a 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), you'll have to set this header manually if you want is_ajax() to work.

HttpRequest.read(size=None)

HttpRequest.readline()

HttpRequest.readlines()

HttpRequest.xreadlines()

HttpRequest.__iter__()
    New in Django 1.3: Please, see the release notes

    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)

UploadedFile objects

class UploadedFile

Attributes

UploadedFile.name

    The name of the uploaded file.

UploadedFile.size

    The size, in bytes, of the uploaded file.

Methods

UploadedFile.chunks(chunk_size=None)

    Returns a generator that yields sequential chunks of data.

UploadedFile.read(num_bytes=None)

    Read a number of bytes from the file.

QueryDict objects

class QueryDict

In an HttpRequest object, the GET and POST attributes are instances of django.http.QueryDict. QueryDict is 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="multiple">, pass multiple values for the same key.

QueryDict instances are immutable, unless you create a copy() of them. That means you can't change attributes of request.POST and request.GET directly.
Methods

QueryDict implements all the standard dictionary methods, because it's a subclass of dictionary. Exceptions are outlined here:

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 Python's 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 (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 doesn't 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 it appends to the current dictionary items rather than replacing them. For example:

    >>> q = QueryDict('a=1')
    >>> q = q.copy() # to make it mutable
    >>> q.update({'a': '2'})
    >>> q.getlist('a')
    [u'1', u'2']
    >>> q['a'] # returns the last
    [u'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()
    [(u'a', u'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()
    [u'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. The copy will be mutable -- that is, you can change its values.

QueryDict.getlist(key, default)

    Returns the data with the requested key, as a Python list. Returns an empty list if the key doesn't exist and no default value was provided. It's guaranteed to return a list of some sort unless the default value was no list.
    Changed in Django Development version: The default parameter was added.

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()
    [(u'a', [u'1', u'2', u'3'])]

QueryDict.dict()
    New in Django Development version.

    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()
    {u'a': u'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'

    Changed in Django 1.3: The safe parameter was added.

    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 an HttpResponse.

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:

>>> response = HttpResponse("Here's the text of the Web page.")
>>> response = HttpResponse("Text only, please.", mimetype="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 passing it hard-coded strings. If you use this technique, follow these guidelines:

    The iterator should return strings.
    If an HttpResponse has been initialized with an iterator as its content, you can't use the HttpResponse instance as a file-like object. Doing so will raise Exception.

Setting headers

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

>>> response = HttpResponse()
>>> response['Cache-Control'] = 'no-cache'
>>> del response['Cache-Control']

Note that unlike a dictionary, del doesn't raise KeyError if the header doesn't exist.

HTTP headers cannot contain newlines. An attempt to set a header 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 mimetype argument and set the Content-Disposition header. For example, this is how you might return a Microsoft Excel spreadsheet:

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

There's nothing Django-specific about the Content-Disposition header, but it's easy to forget the syntax, so we've included it here.
Attributes

HttpResponse.content

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

HttpResponse.status_code

    The HTTP Status code for the response.

Methods

HttpResponse.__init__(content='', mimetype=None, status=200, content_type=DEFAULT_CONTENT_TYPE)

    Instantiates an HttpResponse object with the given page content (a string) and MIME type. The DEFAULT_CONTENT_TYPE is 'text/html'.

    content should be an iterator or a string. If it's 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.

    status is the HTTP Status code for the response.

    content_type is an alias for mimetype. Historically, this parameter was only called mimetype, but since this is actually the value included in the HTTP Content-Type header, it can also include the character set encoding, which makes it more than just a MIME type specification. If mimetype is specified (not None), that value is used. Otherwise, content_type is used. If neither is given, the DEFAULT_CONTENT_TYPE setting is 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 doesn't 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.set_cookie(key, value='', max_age=None, expires=None, path='/', domain=None, secure=None, httponly=False)
    Changed in Django 1.3: Please, see the release notes

    The possibility of specifying a datetime.datetime object in expires, and the auto-calculation of max_age in such case was added. The httponly argument was also added.

    Sets a cookie. The parameters are the same as in the Cookie.Morsel 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 client's 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 isn't 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.

HttpResponse.set_signed_cookie(key, value='', salt='', max_age=None, expires=None, path='/', domain=None, secure=None, httponly=False)
    New in Django Development version.

    Like set_cookie(), but cryptographic signing the cookie before setting it. Use in conjunction with HttpRequest.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 doesn't 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 subclasses

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

class HttpResponseRedirect

    The constructor takes a single argument -- 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/'). Note that this returns an HTTP status code 302.

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 doesn't take any arguments. Use this to designate that a page hasn't been modified since the user's 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. Takes a single, required argument: 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 a SimpleTemplateResponse, and the render method must itself return a valid response object.