Test fail with current packages about primap2

[JGuetschow]

Output from the original error I got from using primap2 in a different project

Traceback (most recent call last):
  File "UNFCCC_GHG_data/UNFCCC_CRF_reader/test_read_UNFCCC_CRF_for_year.py", line 23, in <module>
    read_year_to_test_specs(
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/UNFCCC_GHG_data/UNFCCC_CRF_reader/UNFCCC_CRF_reader_devel.py", line 106, in read_year_to_test_specs
    ds_table_pm2 = pm2.pm2io.from_interchange_format(ds_table_if)
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/primap2/pm2io/_interchange_format.py", line 390, in from_interchange_format
    data_xr.pr.ensure_valid()
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/primap2/_data_format.py", line 101, in ensure_valid
    ensure_valid_data_variables(self._ds)
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/primap2/_data_format.py", line 339, in ensure_valid_data_variables
    ensure_gwp_context_valid(str(key), da)
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/primap2/_data_format.py", line 393, in ensure_gwp_context_valid
    with ureg.context(gwp_context):
  File "/usr/lib/python3.8/contextlib.py", line 113, in __enter__
    return next(self.gen)
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/pint/facets/context/registry.py", line 301, in context
    self.enable_contexts(*names, **kwargs)
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/openscm_units/_unit_registry.py", line 366, in enable_contexts
    self._add_contexts()
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/openscm_units/_unit_registry.py", line 453, in _add_contexts
    self._add_metric_conversions()
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/openscm_units/_unit_registry.py", line 464, in _add_metric_conversions
    self._add_metric_conversions_from_df(metric_conversions)
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/openscm_units/_unit_registry.py", line 471, in _add_metric_conversions_from_df
    for label, val in metric_conversion.iteritems():
  File "/storage/data/data/PRIMAP/primap_2.0/datasets/UNFCCC_non-AnnexI_data/venv/lib/python3.8/site-packages/pandas/core/generic.py", line 5989, in __getattr__
    return object.__getattribute__(self, name)
AttributeError: 'Series' object has no attribute 'iteritems'

[mikapfl]

Shows how important #130 would be…