capybara/virtualenv/lib/python2.7/site-packages/flask/debughelpers.py
def attach_enctype_error_multidict(request):
    """Since Flask 0.8 we're monkeypatching the files object in case a
    request is detected that does not use multipart form data but the files
    object is accessed.
    """
    oldcls = request.files.__class__
    class newcls(oldcls):
        def __getitem__(self, key):
            try:
                return oldcls.__getitem__(self, key)
            except KeyError as e:
                if key not in request.form:
                    raise
                raise DebugFilesKeyError(request, key)
    newcls.__name__ = oldcls.__name__
    newcls.__module__ = oldcls.__module__
    request.files.__class__ = newcls
def attach_enctype_error_multidict(request):
    """Since Flask 0.8 we're monkeypatching the files object in case a
    request is detected that does not use multipart form data but the files
    object is accessed.
    """
    oldcls = request.files.__class__
    class newcls(oldcls):
        def __getitem__(self, key):
            try:
                return oldcls.__getitem__(self, key)
            except KeyError as e:
                if key not in request.form:
                    raise
                raise DebugFilesKeyError(request, key)
    newcls.__name__ = oldcls.__name__
    newcls.__module__ = oldcls.__module__
    request.files.__class__ = newcls
Since Flask 0.8 we're monkeypatching the files object in case a
    request is detected that does not use multipart form data but the files
    object is accessed.