There's some absolutely obscure things here, e.g. h5netcdf.core.BaseVariable._lookup_dimensions:

For 0 datasets:

``` Timer unit: 1e-06 s

Total time: 0.005034 s File: .../python3.8/site-packages/h5netcdf/core.py Function: _lookup_dimensions at line 86

Line # Hits Time Per Hit % Time Line Contents

86                                               def _lookup_dimensions(self):
87         2        633.0    316.5     12.6          attrs = self._h5ds.attrs
88         2         53.0     26.5      1.1          if '_Netcdf4Coordinates' in attrs:
89                                                       order_dim = _reverse_dict(self._parent._dim_order)
90                                                       return tuple(order_dim[coord_id]
91                                                                    for coord_id in attrs['_Netcdf4Coordinates'])
92                                           
93         2        471.0    235.5      9.4          child_name = self.name.split('/')[-1]
94         2         51.0     25.5      1.0          if child_name in self._parent.dimensions:
95                                                       return (child_name,)
96                                           
97         2          4.0      2.0      0.1          dims = []
98         7       1671.0    238.7     33.2          for axis, dim in enumerate(self._h5ds.dims):
99                                                       # TODO: read dimension labels even if there is no associated

100 # scale? it's not netCDF4 spec, but it is unambiguous... 101 # Also: the netCDF lib can read HDF5 datasets with unlabeled 102 # dimensions. 103 5 355.0 71.0 7.1 if len(dim) == 0: 104 raise ValueError('variable %r has no dimension scale ' 105 'associated with axis %s' 106 % (self.name, axis)) 107 5 1772.0 354.4 35.2 name = _name_from_dimension(dim) 108 5 18.0 3.6 0.4 dims.append(name) 109 2 6.0 3.0 0.1 return tuple(dims) ```

For 200 datasets:

``` Timer unit: 1e-06 s

Total time: 2.34179 s File: .../python3.8/site-packages/h5netcdf/core.py Function: _lookup_dimensions at line 86

Line # Hits Time Per Hit % Time Line Contents

86                                               def _lookup_dimensions(self):
87       400      66185.0    165.5      2.8          attrs = self._h5ds.attrs
88       400       6106.0     15.3      0.3          if '_Netcdf4Coordinates' in attrs:
89                                                       order_dim = _reverse_dict(self._parent._dim_order)
90                                                       return tuple(order_dim[coord_id]
91                                                                    for coord_id in attrs['_Netcdf4Coordinates'])
92                                           
93       400      45176.0    112.9      1.9          child_name = self.name.split('/')[-1]
94       400       5006.0     12.5      0.2          if child_name in self._parent.dimensions:
95                                                       return (child_name,)
96                                           
97       400        317.0      0.8      0.0          dims = []
98      1400     168708.0    120.5      7.2          for axis, dim in enumerate(self._h5ds.dims):
99                                                       # TODO: read dimension labels even if there is no associated

100 # scale? it's not netCDF4 spec, but it is unambiguous... 101 # Also: the netCDF lib can read HDF5 datasets with unlabeled 102 # dimensions. 103 1000 35653.0 35.7 1.5 if len(dim) == 0: 104 raise ValueError('variable %r has no dimension scale ' 105 'associated with axis %s' 106 % (self.name, axis)) 107 1000 2012597.0 2012.6 85.9 name = _name_from_dimension(dim) 108 1000 1640.0 1.6 0.1 dims.append(name) 109 400 400.0 1.0 0.0 return tuple(dims) ```