>>> import quantities as pq
>>> pq.__version__
'0.16.1'
>>> aa = pq.UnitQuantity("liter", pq.L, "liter")
>>> pq.CompoundUnit("1/liter")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/hjorth/HBP/Snudda/snudda_env/lib/python3.11/site-packages/quantities/unitquantity.py", line 376, in __new__
    return UnitQuantity.__new__(cls, name, unit_registry[name])
                                           ~~~~~~~~~~~~~^^^^^^
  File "/home/hjorth/HBP/Snudda/snudda_env/lib/python3.11/site-packages/quantities/registry.py", line 73, in __getitem__
    return self.__registry[label]
           ~~~~~~~~~~~~~~~^^^^^^^
  File "/home/hjorth/HBP/Snudda/snudda_env/lib/python3.11/site-packages/quantities/registry.py", line 30, in __getitem__
    raise RuntimeError(f"String parsing error for `{string}`. Enter a string accepted by quantities")
RuntimeError: String parsing error for `1/liter`. Enter a string accepted by quantities

Type "help", "copyright", "credits" or "license" for more information.
>>> import quantities as pq
>>> pq.__version__
'0.14.1'
>>> aa = pq.UnitQuantity("liter", pq.L, "liter")
>>> pq.CompoundUnit("1/liter")
1 (1/liter)
>>> 

>>> import quantities as pq
>>> pq.__version__
'0.16.1'
>>> aa = pq.UnitQuantity("liter", pq.L, "litter")
>>> pq.CompoundUnit("1/litter")
1 (1/litter)
>>>