#13222: unexpected HttpResponse iteration behavior
---------------------------+------------------------------------------------
Reporter: teepark | Owner: nobody
Status: new | Milestone:
Component: HTTP handling | Version: 1.1
Keywords: | Stage: Unreviewed
Has_patch: 0 |
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For all the builtin iterables, and most from libraries, the `__iter__`
method returns something representing one and only one iteration.
`django.http.HttpResponse.__iter__` sets an iterator attribute on itself,
then returns self (it also defines a `next` method so it is its own
iterator). This is bad behavior for an iterable and causes problems when
trying to do anything but basic iteration.
A use case (and where I encountered this issue) is in a WSGI server that
pulls off the first item in the iterable app return value, prefixes
anything that was sent via `write` calls, and then rebuilds the iterable
with `itertools.chain`:
{{{
if prefix:
body_iterator = iter(body)
try:
first_chunk = body_iterator.next()
except StopIteration:
first_chunk = ''
body = itertools.chain((prefix + first_chunk,), body_iterator)
}}}
Using `django.core.handlers.wsgi.WSGIHandler` (which just returns the
HttpResponse, since it's iterable) with this server, the first chunk of
the HttpResponse gets doubled because `itertools.chain` calls `iter` on
its arguments, and that resets the HttpResponse's iterator.
To compare with some builtins and other libraries:
{{{
>>> it = iter(["foobar"])
>>> list(it), list(it)
(['foobar'], [])
>>> it = iter("foobar" for i in [1])
>>> list(it), list(it)
(['foobar'], [])
>>> import werkzeug
>>> it = iter(werkzeug.Response("foobar").response)
>>> list(it), list(it)
(['foobar'], [])
>>> import webob
>>> it = iter(webob.Response("foobar").app_iter)
>>> list(it), list(it)
(['foobar'], [])
>>> import django.http
>>> it = iter(django.http.HttpResponse("foobar"))
>>> list(it), list(it)
(['foobar'], ['foobar'])
}}}
--
Ticket URL: <http://code.djangoproject.com/ticket/13222>
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