keep attrs of get_bitinformation

[aaronspring]

closes #154

• changes units to bitinfo_units
• changes long_name to bitinfo_long_name
• keep input attrs

[observingClouds]

Could you please explain why you would like to have the original units and long_name from the dataset? Do we loose these attributes when writing to netCDF/zarr?
The unit of the data that info_per_bit = xb.get_bitinformation(ds) contains is 1 and not e.g. ms-1 if the input data was wind speed.

[aaronspring]

I want to keep long_name and all other attrs for context. Now we only have the variable name and no context from the input data. Original unit might not be very important

[aaronspring]

Now the bitinformation of z, in reference to what z actually is, is easier to understand IMO.

[observingClouds]

The attributes are preserved in ds_bitrounded:

In [11]: ds_bitrounded.u
Out[11]: 
<xarray.DataArray 'u' (month: 2, level: 3, latitude: 241, longitude: 480)>
array([[[[ 1.250000e+00,  1.250000e+00,  1.250000e+00, ...,
         [ 3.500000e+00,  3.500000e+00,  3.500000e+00, ...,
           3.750000e+00,  3.500000e+00,  3.500000e+00]]]], dtype=float32)
Coordinates:
  * longitude  (longitude) float32 -180.0 -179.2 -178.5 ... 177.8 178.5 179.2
  * latitude   (latitude) float32 90.0 89.25 88.5 87.75 ... -88.5 -89.25 -90.0
  * level      (level) int32 200 500 850
  * month      (month) int32 1 7
Attributes:
    number_of_significant_digits:                2
    units:                                       m s**-1
    long_name:                                   U component of wind
    standard_name:                               eastward_wind
    _QuantizeBitRoundNumberOfSignificantDigits:  3

[aaronspring]

I know. I just refered to info_per_bit the output from get_bitinformation

[observingClouds]

I don't really like this PR yet, mainly because the units, long_name and standard_name attributes are cf-conventions conform attributes that describe the attributes of the variable and not the ones they are derived from.
A compromise could be to prefix the attributes from the input dataset with e.g. source_, so that there would be source_units = m**2 s**-2, source_standard_name = geopotential etc. So instead of prefixing the bitinformation attributes, the original dataset attributes get a prefix. Would that help?

[aaronspring]

I like the source idea