thirdparty/google_appengine/lib/webob/docs/file-example.txt
author Sverre Rabbelier <srabbelier@gmail.com>
Wed, 11 Feb 2009 23:42:03 +0000
changeset 1267 157c12589f79
parent 109 620f9b141567
permissions -rw-r--r--
Make it possible to put fields at the end of the form This is usefull for Terms of Service etc. Patch by: Sverre Rabbelier
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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WebOb File-Serving Example
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==========================
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This document shows how you can make a static-file-serving application
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using WebOb.  We'll quickly build this up from minimal functionality
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to a high-quality file serving application.
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.. comment:
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   >>> import webob, os
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   >>> base_dir = os.path.dirname(os.path.dirname(webob.__file__))
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   >>> doc_dir = os.path.join(base_dir, 'docs')
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   >>> from dtopt import ELLIPSIS
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First we'll setup a really simple shim around our application, which
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we can use as we improve our application:
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.. code-block::
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   >>> from webob import Request, Response
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   >>> import os
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   >>> class FileApp(object):
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   ...     def __init__(self, filename):
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   ...         self.filename = filename
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   ...     def __call__(self, environ, start_response):
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   ...         res = make_response(self.filename)
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   ...         return res(environ, start_response)
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   >>> import mimetypes
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   >>> def get_mimetype(filename):
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   ...     type, encoding = mimetypes.guess_type(filename)
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   ...     # We'll ignore encoding, even though we shouldn't really
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   ...     return type or 'application/octet-stream'
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Now we can make different definitions of ``make_response``.  The
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simplest version:
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.. code-block::
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   >>> def make_response(filename):
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   ...     res = Response(content_type=get_mimetype(filename))
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   ...     res.body = open(filename, 'rb').read()
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   ...     return res
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Let's give it a go.  We'll test it out with a file ``test-file.txt``
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in the WebOb doc directory:
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.. code-block::
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   >>> fn = os.path.join(doc_dir, 'test-file.txt')
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   >>> open(fn).read()
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   'This is a test.  Hello test people!\n'
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   >>> app = FileApp(fn)
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   >>> req = Request.blank('/')
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   >>> print req.get_response(app)
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   200 OK
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   content-type: text/plain
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   Content-Length: 36
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   <BLANKLINE>
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   This is a test.  Hello test people!
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   <BLANKLINE>
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Well, that worked.  But it's not a very fancy object.  First, it reads
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everything into memory, and that's bad.  We'll create an iterator instead:
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.. code-block::
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   >>> class FileIterable(object):
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   ...     def __init__(self, filename):
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   ...         self.filename = filename
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   ...     def __iter__(self):
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   ...         return FileIterator(self.filename)
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   >>> class FileIterator(object):
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   ...     chunk_size = 4096
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   ...     def __init__(self, filename):
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   ...         self.filename = filename
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   ...         self.fileobj = open(self.filename, 'rb')
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   ...     def __iter__(self):
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   ...         return self
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   ...     def next(self):
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   ...         chunk = self.fileobj.read(self.chunk_size)
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   ...         if not chunk:
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   ...             raise StopIteration
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   ...         return chunk
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   >>> def make_response(filename):
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   ...     res = Response(content_type=get_mimetype(filename))
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   ...     res.app_iter = FileIterable(filename)
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   ...     res.content_length = os.path.getsize(filename)
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   ...     return res
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And testing:
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.. code-block::
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   >>> req = Request.blank('/')
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   >>> print req.get_response(app)
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   200 OK
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   content-type: text/plain
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   Content-Length: 36
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   <BLANKLINE>
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   This is a test.  Hello test people!
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   <BLANKLINE>
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Well, that doesn't *look* different, but lets *imagine* that it's
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different because we know we changed some code.  Now to add some basic
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metadata to the response:
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.. code-block::
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   >>> def make_response(filename):
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   ...     res = Response(content_type=get_mimetype(filename),
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   ...                    conditional_response=True)
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   ...     res.app_iter = FileIterable(filename)
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   ...     res.content_length = os.path.getsize(filename)
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   ...     res.last_modified = os.path.getmtime(filename)
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   ...     res.etag = '%s-%s-%s' % (os.path.getmtime(filename),
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   ...                              os.path.getsize(filename), hash(filename))
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   ...     return res
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Now, with ``conditional_response`` on, and with ``last_modified`` and
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``etag`` set, we can do conditional requests:
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.. code-block::
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   >>> req = Request.blank('/')
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   >>> res = req.get_response(app)
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   >>> print res
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   200 OK
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   content-type: text/plain
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   Content-Length: 36
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   Last-Modified: ... GMT
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   ETag: ...-...
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   <BLANKLINE>
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   This is a test.  Hello test people!
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   <BLANKLINE>
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   >>> req2 = Request.blank('/')
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   >>> req2.if_none_match = res.etag
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   >>> req2.get_response(app)
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   <Response ... 304 Not Modified>
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   >>> req3 = Request.blank('/')
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   >>> req3.if_modified_since = res.last_modified
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   >>> req3.get_response(app)
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   <Response ... 304 Not Modified>
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We can even do Range requests, but it will currently involve iterating
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through the file unnecessarily.  When there's a range request (and you
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set ``conditional_response=True``) the application will satisfy that
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request.  But with an arbitrary iterator the only way to do that is to
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run through the beginning of the iterator until you get to the chunk
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that the client asked for.  We can do better because we can use
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``fileobj.seek(pos)`` to move around the file much more efficiently.
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So we'll add an extra method, ``app_iter_range``, that ``Response``
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looks for:
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.. code-block::
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   >>> class FileIterable(object):
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   ...     def __init__(self, filename, start=None, stop=None):
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   ...         self.filename = filename
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   ...         self.start = start
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   ...         self.stop = stop
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   ...     def __iter__(self):
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   ...         return FileIterator(self.filename, self.start, self.stop)
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   ...     def app_iter_range(self, start, stop):
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   ...         return self.__class__(self.filename, start, stop)
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   >>> class FileIterator(object):
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   ...     chunk_size = 4096
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   ...     def __init__(self, filename, start, stop):
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   ...         self.filename = filename
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   ...         self.fileobj = open(self.filename, 'rb')
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   ...         if start:
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   ...             self.fileobj.seek(start)
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   ...         if stop is not None:
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   ...             self.length = stop - start
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   ...         else:
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   ...             self.length = None
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   ...     def __iter__(self):
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   ...         return self
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   ...     def next(self):
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   ...         if self.length is not None and self.length <= 0:
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   ...             raise StopIteration
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   ...         chunk = self.fileobj.read(self.chunk_size)
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   ...         if not chunk:
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   ...             raise StopIteration
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   ...         if self.length is not None:
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   ...             self.length -= len(chunk)
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   ...             if self.length < 0:
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   ...                 # Chop off the extra:
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   ...                 chunk = chunk[:self.length]
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   ...         return chunk
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Now we'll test it out:
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.. code-block::
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   >>> req = Request.blank('/')
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   >>> res = req.get_response(app)
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   >>> req2 = Request.blank('/')
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   >>> # Re-fetch the first 5 bytes:
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   >>> req2.range = (0, 5)
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   >>> res2 = req2.get_response(app)
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   >>> res2
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   <Response ... 206 Partial Content>
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   >>> # Let's check it's our custom class:
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   >>> res2.app_iter
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   <FileIterable object at ...>
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   >>> res2.body
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   'This '
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   >>> # Now, conditional range support:
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   >>> req3 = Request.blank('/')
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   >>> req3.if_range = res.etag
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   >>> req3.range = (0, 5)
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   >>> req3.get_response(app)
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   <Response ... 206 Partial Content>
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   >>> req3.if_range = 'invalid-etag'
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   >>> req3.get_response(app)
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   <Response ... 200 OK>