human
Complete this python program:
def _flattenTree(request, root, write):
assistant
#Here is the Python code you requested.

    """Make C{root} into an iterable of L{bytes} and L{Deferred} by doing a depth
    first traversal of the tree.
    @param request: A request object which will be passed to
    L{IRenderable.render}.
    @param root: An object to be made flatter.  This may be of type C{unicode},
    L{bytes}, L{slot}, L{Tag <twisted.web.template.Tag>}, L{tuple},
    L{list}, L{types.GeneratorType}, L{Deferred}, or something providing
    L{IRenderable}.
    @param write: A callable which will be invoked with each L{bytes} produced
    by flattening C{root}.
    @return: An iterator which yields objects of type L{bytes} and L{Deferred}.
    A L{Deferred} is only yielded when one is encountered in the process of
    flattening C{root}.  The returned iterator must not be iterated again
    until the L{Deferred} is called back.
    """
    stack = [_flattenElement(request, root, write, [], None, escapeForContent)]
    while stack:
        try:
            frame = stack[(-1)].gi_frame
            element = next(stack[(-1)])
        except StopIteration:
            stack.pop()
        except Exception as e:
            stack.pop()
            roots = []
            for generator in stack:
                roots.append(generator.gi_frame.f_locals['root'])
            roots.append(frame.f_locals['root'])
            raise FlattenerError(e, roots, extract_tb(exc_info()[2]))
        else:
            if isinstance(element, Deferred):
                def cbx(originalAndToFlatten):
                    (original, toFlatten) = originalAndToFlatten
                    stack.append(toFlatten)
                    return original
                (yield element.addCallback(cbx))
            else:
                stack.append(element)