Let me be more precise:
My suggestion is not to remove `unconsumed_tail` entirely, but I think its value needs to be defined only when the end of the compressed stream has been reached.
In other words, you could still do:
while not decomp.eof
# ...
if decomp.unconsumed_tail:
raise RuntimeError('unexpected data after end of compressed stream')
but as long as decomp.eof is True, decomp.unconsumed_tail could (as far as I can tell) be None, no matter if there is uncompressed data in the internal buffer or not.