attaching new patch. this implements the memoryview solution suggested by pitrou. but it does contain this thing:

if not request.has_header('Content-length'):
    if (not hasattr(data, '__read__') and 
        isinstance(data, collections.Iterable)):
        print(data,"is an iterable")
        try:
            m = memoryview(data)
            print(m.itemsize * len(m))
            request.add_unredirected_header(
                'Content-length', '%d' % (len(m) * m.itemsize))
        except TypeError:
            try:
                request.add_unredirected_header(
                    'Content-length', '%d' % len(data))
            except TypeError:
                raise ValueError(
                    "No Content-Length specified for iterable body")

why is it so nested? because data can support 3 different interfaces:

1) Buffer interface, in that case use memoryview to count bytes
2) Can call len but not buffer: assume len == #bytes
3) Iterable but cannot call len or memoryview: raise ValueError

I hope there is a simpler way...