If ``query_string`` is not passed in, the resulting ``QueryDict`` will be
empty (it will have no keys or values).
Most ``QueryDict``\ s 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 :setting:`DEFAULT_CHARSET`.
.. versionchanged:: 1.8
In previous versions, ``query_string`` was a required positional argument.
.. method:: 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``.)
.. method:: 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()``).
.. method:: QueryDict.__contains__(key)
Returns ``True`` if the given key is set. This lets you do, e.g., ``if "foo"
in request.GET``.
.. method:: 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.
.. method:: QueryDict.setdefault(key, default)
Just like the standard dictionary ``setdefault()`` method, except it uses
``__setitem__()`` internally.
.. method:: 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', mutable=True)
>>> q.update({'a': '2'})
>>> q.getlist('a')
['1', '2']
>>> q['a'] # returns the last
['2']
.. method:: 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')]
.. method:: QueryDict.iteritems()
Just like the standard dictionary ``iteritems()`` method. Like
:meth:`QueryDict.items()` this uses the same last-value logic as
:meth:`QueryDict.__getitem__()`.
.. method:: QueryDict.iterlists()
Like :meth:`QueryDict.iteritems()` except it includes all values, as a list,
for each member of the dictionary.
.. method:: 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']
.. method:: QueryDict.itervalues()
Just like :meth:`QueryDict.values()`, except an iterator.
In addition, ``QueryDict`` has the following methods:
.. method:: 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.
.. method:: 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.
.. method:: QueryDict.setlist(key, list_)
Sets the given key to ``list_`` (unlike ``__setitem__()``).
.. method:: QueryDict.appendlist(key, item)
Appends an item to the internal list associated with key.
.. method:: QueryDict.setlistdefault(key, default_list)
Just like ``setdefault``, except it takes a list of values instead of a
single value.
.. method:: QueryDict.lists()
Like :meth:`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'])]
.. method:: 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']
.. method:: QueryDict.popitem()
Removes an arbitrary member of the dictionary (since there's 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'])
.. method:: 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 :meth:`QueryDict.__getitem__()`::
>>> q = QueryDict('a=1&a=3&a=5')
>>> q.dict()
{'a': '5'}
.. method:: 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 :class:`HttpRequest` objects, which are created automatically by
Django, :class:`HttpResponse` objects are your responsibility. Each view you
write is responsible for instantiating, populating and returning an
:class:`HttpResponse`.
The :class:`HttpResponse` class lives in the :mod:`django.http` module.
Usage
-----
Passing strings
~~~~~~~~~~~~~~~
Typical usage is to pass the contents of the page, as a string, to the
:class:`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("Here's the text of the Web page.
")
>>> response.write("Here's another paragraph.
")
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 the :class:`StreamingHttpResponse` 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`` doesn't raise ``KeyError`` if the header
field doesn't exist.
For setting the ``Cache-Control`` and ``Vary`` header fields, it is recommended
to use the :func:`~django.utils.cache.patch_cache_control` and
:func:`~django.utils.cache.patch_vary_headers` methods from
:mod:`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 the ``Content-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"'
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
----------
.. attribute:: HttpResponse.content
A bytestring representing the content, encoded from a Unicode
object if necessary.
.. attribute:: HttpResponse.charset
.. versionadded:: 1.8
A string denoting the charset in which the response will be encoded. If not
given at ``HttpResponse`` instantiation time, it will be extracted from
``content_type`` and if that is unsuccessful, the
:setting:`DEFAULT_CHARSET` setting will be used.
.. attribute:: HttpResponse.status_code
The `HTTP status code`_ for the response.
.. attribute:: HttpResponse.reason_phrase
The HTTP reason phrase for the response.
.. attribute:: HttpResponse.streaming
This is always ``False``.
This attribute exists so middleware can treat streaming responses
differently from regular responses.
Methods
-------
.. method:: 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 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.
``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 :setting:`DEFAULT_CONTENT_TYPE` and
:setting:`DEFAULT_CHARSET` settings, 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 from ``content_type``, and if that
is unsuccessful, the :setting:`DEFAULT_CHARSET` setting will be used.
.. versionadded:: 1.8
The ``charset`` parameter was added.
.. method:: HttpResponse.__setitem__(header, value)
Sets the given header name to the given value. Both ``header`` and
``value`` should be strings.
.. method:: HttpResponse.__delitem__(header)
Deletes the header with the given name. Fails silently if the header
doesn't exist. Case-insensitive.
.. method:: HttpResponse.__getitem__(header)
Returns the value for the given header name. Case-insensitive.
.. method:: HttpResponse.has_header(header)
Returns ``True`` or ``False`` based on a case-insensitive check for a
header with the given name.
.. method:: 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
:class:`~http.cookies.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 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.
.. _HTTPOnly: https://www.owasp.org/index.php/HTTPOnly
.. 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 there's an attempt
to store a cookie of more than 4096 bytes, but many browsers will not
set the cookie correctly.
.. method:: HttpResponse.set_signed_cookie(key, value, salt='', max_age=None, expires=None, path='/', domain=None, secure=None, httponly=True)
Like :meth:`~HttpResponse.set_cookie()`, but
:doc:`cryptographic signing ` the cookie before setting
it. Use in conjunction with :meth:`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
:meth:`HttpRequest.get_signed_cookie` call.
.. method:: 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.
.. method:: HttpResponse.write(content)
This method makes an :class:`HttpResponse` instance a file-like object.
.. method:: HttpResponse.flush()
This method makes an :class:`HttpResponse` instance a file-like object.
.. method:: HttpResponse.tell()
This method makes an :class:`HttpResponse` instance a file-like object.
.. _HTTP status code: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10
.. _ref-httpresponse-subclasses:
HttpResponse subclasses
-----------------------
Django includes a number of ``HttpResponse`` subclasses that handle different
types of HTTP responses. Like ``HttpResponse``, these subclasses live in
:mod:`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 :class:`HttpResponse` for other optional
constructor arguments. Note that this returns an HTTP status code 302.
.. attribute:: HttpResponseRedirect.url
This read-only attribute represents the URL the response will redirect
to (equivalent to the ``Location`` response header).
.. class:: HttpResponsePermanentRedirect
Like :class:`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 and no content should be added
to this response. 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 :class:`HttpResponse` but uses a 400 status code.
.. class:: HttpResponseNotFound
Acts just like :class:`HttpResponse` but uses a 404 status code.
.. class:: HttpResponseForbidden
Acts just like :class:`HttpResponse` but uses a 403 status code.
.. class:: HttpResponseNotAllowed
Like :class:`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 :class:`HttpResponse` but uses a 410 status code.
.. class:: HttpResponseServerError
Acts just like :class:`HttpResponse` but uses a 500 status code.
.. note::
If a custom subclass of :class:`HttpResponse` implements a ``render``
method, Django will treat it as emulating a
:class:`~django.template.response.SimpleTemplateResponse`, and the
``render`` method must itself return a valid response object.
JsonResponse objects
====================
.. versionadded:: 1.7
.. class:: JsonResponse
.. method:: JsonResponse.__init__(data, encoder=DjangoJSONEncoder, safe=True, **kwargs)
An :class:`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. See :ref:`JSON serialization
` for more details about this serializer.
The ``safe`` boolean parameter defaults to ``True``. If it's 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 :exc:`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 :exc:`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
:class:`~django.http.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 differ JSON encoder class you can pass the ``encoder``
parameter to the constructor method::
>>> response = JsonResponse(data, encoder=MyJSONEncoder)
.. _httpresponse-streaming:
StreamingHttpResponse objects
=============================
.. class:: StreamingHttpResponse
The :class:`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, it's useful for
:ref:`generating large CSV files `.
.. admonition:: 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 :class:`StreamingHttpResponse` is not a subclass of :class:`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
:attr:`~StreamingHttpResponse.streaming_content` attribute.
* You cannot use the file-like object ``tell()`` or ``write()`` methods.
Doing so will raise an exception.
:class:`StreamingHttpResponse` should only be used in situations where it is
absolutely required that the whole content isn't iterated before transferring
the data to the client. Because the content can't be accessed, many
middlewares can't function normally. For example the ``ETag`` and ``Content-
Length`` headers can't be generated for streaming responses.
Attributes
----------
.. attribute:: StreamingHttpResponse.streaming_content
An iterator of strings representing the content.
.. attribute:: StreamingHttpResponse.status_code
The `HTTP status code`_ for the response.
.. attribute:: StreamingHttpResponse.reason_phrase
The HTTP reason phrase for the response.
.. attribute:: StreamingHttpResponse.streaming
This is always ``True``.