+
−============================
+
−Request and response objects
+
−============================
+
−
+
−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
+
−===================
+
−
+
−Attributes
+
−----------
+
−
+
−All attributes except ``session`` should be considered read-only.
+
−
+
−``path``
+
−    A string representing the full path to the requested page, not including
+
−    the domain.
+
−
+
−    Example: ``"/music/bands/the_beatles/"``
+
−
+
−``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()
+
−
+
−``GET``
+
−    A dictionary-like object containing all given HTTP GET parameters. See the
+
−    ``QueryDict`` documentation below.
+
−
+
−``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``.
+
−
+
−``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.
+
−
+
−``COOKIES``
+
−    A standard Python dictionary containing all cookies. Keys and values are
+
−    strings.
+
−
+
−``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 a standard Python dictionary with the following three
+
−    keys:
+
−
+
−        * ``filename`` -- The name of the uploaded file, as a Python string.
+
−        * ``content-type`` -- The content type of the uploaded file.
+
−        * ``content`` -- The raw content of the uploaded file.
+
−
+
−    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.
+
−
+
−``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``
+
−        * ``CONTENT_TYPE``
+
−        * ``HTTP_ACCEPT_ENCODING``
+
−        * ``HTTP_ACCEPT_LANGUAGE``
+
−        * ``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.
+
−        * ``REQUEST_METHOD`` -- A string such as ``"GET"`` or ``"POST"``.
+
−        * ``SERVER_NAME`` -- The hostname of the server.
+
−        * ``SERVER_PORT`` -- The port of the server.
+
−
+
−``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
+
−    `Authentication in Web requests`_.
+
−
+
−    .. _Authentication in Web requests: ../authentication/#authentication-in-web-requests
+
−
+
−``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.
+
−
+
−    .. _`session documentation`: ../sessions/
+
−
+
−``raw_post_data``
+
−    The raw HTTP POST data. This is only useful for advanced processing. Use
+
−    ``POST`` instead.
+
−
+
−Methods
+
−-------
+
−
+
−``__getitem__(key)``
+
−   Returns the GET/POST value for the given key, checking POST first, then
+
−   GET. Raises ``KeyError`` if the key doesn't exist.
+
−
+
−   This lets you use dictionary-accessing syntax on an ``HttpRequest``
+
−   instance. Example: ``request["foo"]`` would return ``True`` if either
+
−   ``request.POST`` or ``request.GET`` had a ``"foo"`` key.
+
−
+
−``has_key()``
+
−   Returns ``True`` or ``False``, designating whether ``request.GET`` or
+
−   ``request.POST`` has the given key.
+
−
+
−``get_full_path()``
+
−   Returns the ``path``, plus an appended query string, if applicable.
+
−
+
−   Example: ``"/music/bands/the_beatles/?print=true"``
+
−
+
−``is_secure()``
+
−   Returns ``True`` if the request is secure; that is, if it was made with
+
−   HTTPS.
+
−
+
−QueryDict objects
+
−-----------------
+
−
+
−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.
+
−
+
−``QueryDict`` implements the all standard dictionary methods, because it's a
+
−subclass of dictionary. Exceptions are outlined here:
+
−
+
−    * ``__getitem__(key)`` -- Returns the value for the given key. If the key
+
−      has more than one value, ``__getitem__()`` returns the last value.
+
−
+
−    * ``__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()``).
+
−
+
−    * ``__contains__(key)`` -- Returns ``True`` if the given key is set. This
+
−      lets you do, e.g., ``if "foo" in request.GET``.
+
−
+
−    * ``get(key, default)`` -- Uses the same logic as ``__getitem__()`` above,
+
−      with a hook for returning a default value if the key doesn't exist.
+
−
+
−    * ``has_key(key)``
+
−
+
−    * ``setdefault(key, default)`` -- Just like the standard dictionary
+
−      ``setdefault()`` method, except it uses ``__setitem__`` internally.
+
−
+
−    * ``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')
+
−          ['1', '2']
+
−          >>> q['a'] # returns the last
+
−          ['2']
+
−
+
−    * ``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')]
+
−
+
−    * ``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']
+
−
+
−In addition, ``QueryDict`` has the following methods:
+
−
+
−    * ``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.
+
−
+
−    * ``getlist(key)`` -- Returns the data with the requested key, as a Python
+
−      list. Returns an empty list if the key doesn't exist. It's guaranteed to
+
−      return a list of some sort.
+
−
+
−    * ``setlist(key, list_)`` -- Sets the given key to ``list_`` (unlike
+
−      ``__setitem__()``).
+
−
+
−    * ``appendlist(key, item)`` -- Appends an item to the internal list
+
−      associated with key.
+
−
+
−    * ``setlistdefault(key, default_list)`` -- Just like ``setdefault``, except
+
−      it takes a list of values instead of a single value.
+
−
+
−    * ``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'])]
+
−
+
−    * ``urlencode()`` -- Returns a string of the data in query-string format.
+
−      Example: ``"a=2&b=3&b=5"``.
+
−
+
−Examples
+
−--------
+
−
+
−Here's an example HTML form and how Django would treat the input::
+
−
+
−    <form action="/foo/bar/" method="post">
+
−    <input type="text" name="your_name" />
+
−    <select multiple="multiple" name="bands">
+
−        <option value="beatles">The Beatles</option>
+
−        <option value="who">The Who</option>
+
−        <option value="zombies">The Zombies</option>
+
−    </select>
+
−    <input type="submit" />
+
−    </form>
+
−
+
−If the user enters ``"John Smith"`` in the ``your_name`` field and selects both
+
−"The Beatles" and "The Zombies" in the multiple select box, here's what
+
−Django's request object would have::
+
−
+
−    >>> request.GET
+
−    {}
+
−    >>> request.POST
+
−    {'your_name': ['John Smith'], 'bands': ['beatles', 'zombies']}
+
−    >>> request.POST['your_name']
+
−    'John Smith'
+
−    >>> request.POST['bands']
+
−    'zombies'
+
−    >>> request.POST.getlist('bands')
+
−    ['beatles', 'zombies']
+
−    >>> request.POST.get('your_name', 'Adrian')
+
−    'John Smith'
+
−    >>> request.POST.get('nonexistent_field', 'Nowhere Man')
+
−    'Nowhere Man'
+
−
+
−Implementation notes
+
−--------------------
+
−
+
−The ``GET``, ``POST``, ``COOKIES``, ``FILES``, ``META``, ``REQUEST``,
+
−``raw_post_data`` and ``user`` attributes are all lazily loaded. That means
+
−Django doesn't spend resources calculating the values of those attributes until
+
−your code requests them.
+
−
+
−HttpResponse objects
+
−====================
+
−
+
−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 at ``django.http.HttpResponse``.
+
−
+
−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>")
+
−
+
−You can add and delete headers using dictionary syntax::
+
−
+
−    >>> response = HttpResponse()
+
−    >>> response['X-DJANGO'] = "It's the best."
+
−    >>> del response['X-PHP']
+
−    >>> response['X-DJANGO']
+
−    "It's the best."
+
−
+
−Note that ``del`` doesn't raise ``KeyError`` if the header doesn't exist.
+
−
+
−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``.
+
−
+
−Methods
+
−-------
+
−
+
−``__init__(content='', mimetype=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`` can 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.
+
−
+
−``__setitem__(header, value)``
+
−    Sets the given header name to the given value. Both ``header`` and
+
−    ``value`` should be strings.
+
−
+
−``__delitem__(header)``
+
−    Deletes the header with the given name. Fails silently if the header
+
−    doesn't exist. Case-sensitive.
+
−
+
−``__getitem__(header)``
+
−    Returns the value for the given header name. Case-sensitive.
+
−
+
−``has_header(header)``
+
−    Returns ``True`` or ``False`` based on a case-insensitive check for a
+
−    header with the given name.
+
−
+
−``set_cookie(key, value='', max_age=None, expires=None, path='/', domain=None, secure=None)``
+
−    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.
+
−        * ``expires`` should be a string in the format
+
−          ``"Wdy, DD-Mon-YY HH:MM:SS GMT"``.
+
−        * 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.
+
−
+
−    .. _`cookie Morsel`: http://www.python.org/doc/current/lib/morsel-objects.html
+
−
+
−``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.
+
−
+
−``content``
+
−    Returns the content as a Python string, encoding it from a Unicode object
+
−    if necessary. Note this is a property, not a method, so use ``r.content``
+
−    instead of ``r.content()``.
+
−
+
−``write(content)``, ``flush()`` and ``tell()``
+
−    These methods make 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``.
+
−
+
−``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 URL with no domain (e.g. ``'/search/'``). Note that this returns
+
−    an HTTP status code 302.
+
−
+
−``HttpResponsePermanentRedirect``
+
−    Like ``HttpResponseRedirect``, but it returns a permanent redirect (HTTP
+
−    status code 301) instead of a "found" redirect (status code 302).
+
−
+
−``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.
+
−
+
−``HttpResponseNotFound``
+
−    Acts just like ``HttpResponse`` but uses a 404 status code.
+
−
+
−``HttpResponseForbidden``
+
−    Acts just like ``HttpResponse`` but uses a 403 status code.
+
−
+
−``HttpResponseNotAllowed``
+
−    Like ``HttpResponse``, but uses a 405 status code. Takes a single,
+
−    required argument: a list of permitted methods (e.g. ``['GET', 'POST']``).
+
−
+
−``HttpResponseGone``
+
−    Acts just like ``HttpResponse`` but uses a 410 status code.
+
−
+
−``HttpResponseServerError``
+
−    Acts just like ``HttpResponse`` but uses a 500 status code.
+
−
+
−Returning errors
+
−================
+
−
+
−Returning HTTP error codes in Django is easy. We've already mentioned the
+
−``HttpResponseNotFound``, ``HttpResponseForbidden``,
+
−``HttpResponseServerError``, etc., subclasses; just return an instance of one
+
−of those subclasses instead of a normal ``HttpResponse`` in order to signify
+
−an error. For example::
+
−
+
−    def my_view(request):
+
−        # ...
+
−        if foo:
+
−            return HttpResponseNotFound('<h1>Page not found</h1>')
+
−        else:
+
−            return HttpResponse('<h1>Page was found</h1>')
+
−
+
−Because 404 errors are by far the most common HTTP error, there's an easier way
+
−to handle those errors.
+
−
+
−The Http404 exception
+
−---------------------
+
−
+
−When you return an error such as ``HttpResponseNotFound``, you're responsible
+
−for defining the HTML of the resulting error page::
+
−
+
−    return HttpResponseNotFound('<h1>Page not found</h1>')
+
−
+
−For convenience, and because it's a good idea to have a consistent 404 error page
+
−across your site, Django provides an ``Http404`` exception. If you raise
+
−``Http404`` at any point in a view function, Django will catch it and return the
+
−standard error page for your application, along with an HTTP error code 404.
+
−
+
−Example usage::
+
−
+
−    from django.http import Http404
+
−
+
−    def detail(request, poll_id):
+
−        try:
+
−            p = Poll.objects.get(pk=poll_id)
+
−        except Poll.DoesNotExist:
+
−            raise Http404
+
−        return render_to_response('polls/detail.html', {'poll': p})
+
−
+
−In order to use the ``Http404`` exception to its fullest, you should create a
+
−template that is displayed when a 404 error is raised. This template should be
+
−called ``404.html`` and located in the top level of your template tree.
+
−
+
−Customing error views
+
−---------------------
+
−
+
−The 404 (page not found) view
+
−~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
−
+
−When you raise an ``Http404`` exception, Django loads a special view devoted
+
−to handling 404 errors. By default, it's the view
+
−``django.views.defaults.page_not_found``, which loads and renders the template
+
−``404.html``.
+
−
+
−This means you need to define a ``404.html`` template in your root template
+
−directory. This template will be used for all 404 errors.
+
−
+
−This ``page_not_found`` view should suffice for 99% of Web applications, but if
+
−you want to override the 404 view, you can specify ``handler404`` in your
+
−URLconf, like so::
+
−
+
−    handler404 = 'mysite.views.my_custom_404_view'
+
−
+
−Behind the scenes, Django determines the 404 view by looking for ``handler404``.
+
−By default, URLconfs contain the following line::
+
−
+
−    from django.conf.urls.defaults import *
+
−
+
−That takes care of setting ``handler404`` in the current module. As you can see
+
−in ``django/conf/urls/defaults.py``, ``handler404`` is set to
+
−``'django.views.defaults.page_not_found'`` by default.
+
−
+
−Three things to note about 404 views:
+
−
+
−    * The 404 view is also called if Django doesn't find a match after checking
+
−      every regular expression in the URLconf.
+
−
+
−    * If you don't define your own 404 view -- and simply use the default,
+
−      which is recommended -- you still have one obligation: To create a
+
−      ``404.html`` template in the root of your template directory. The default
+
−      404 view will use that template for all 404 errors.
+
−
+
−    * If ``DEBUG`` is set to ``True`` (in your settings module) then your 404
+
−      view will never be used, and the traceback will be displayed instead.
+
−
+
−The 500 (server error) view
+
−~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
−
+
−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 loads and renders the
+
−template ``500.html``.
+
−
+
−This means you need to define a ``500.html`` template in your root template
+
−directory. This template will be used for all server errors.
+
−
+
−This ``server_error`` view should suffice for 99% of Web applications, but if
+
−you want to override the view, you can specify ``handler500`` in your
+
−URLconf, like so::
+
−
+
−    handler500 = 'mysite.views.my_custom_error_view'
+
−
+
−Behind the scenes, Django determines the error view by looking for ``handler500``.
+
−By default, URLconfs contain the following line::
+
−
+
−    from django.conf.urls.defaults import *
+
−
+
−That takes care of setting ``handler500`` in the current module. As you can see
+
−in ``django/conf/urls/defaults.py``, ``handler500`` is set to
+
−``'django.views.defaults.server_error'`` by default.