Incompatible differences between versions 1.x and 2.x

Note

For versions 3.x (Python 3) documentation, see https://ncas-cms.github.io/cf-python

For those familiar with the cf-python API at version 1.x, some important, backwards incompatible changes were introduced at version 2.0.

Some of these changes could break code written at version 1.x, causing an exception to be raised. For others, those marked with a warning, version 1.x may work but could produce scientifically different results.

All of the changes have been designed to make the interface more consistent and intuitive to use and were introduced at version 2.0 to coincide with the updated CF data model structure.

attributes

Note

At version 2.x cf.Field.attributes is callable and allows the attributes to be updated inplace.

>>> cf.__version__
2.0
>>> f.attributes()
{'ncvar': 'tas'}

At version 1.x it wasn’t callable and returned a dict copy of the attributes.

axes

Note

At version 2.x cf.Field.axes returns, by default, a dict. If the ordered parameter is True then it returns an OrderedDict.

>>> cf.__version__
2.0
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>
>>> f.axes()
{'dim0': <CF DomainAxis: 12>,
 'dim1': <CF DomainAxis: 64>,
 'dim2': <CF DomainAxis: 128>,
 'dim3': <CF DomainAxis: 1>}
>>> f.axes(ordered=True)
OrderedDict([('dim3', <CF DomainAxis: 1>),
             ('dim0', <CF DomainAxis: 12>),
             ('dim1', <CF DomainAxis: 64>),
             ('dim2', <CF DomainAxis: 128>)])

At version 1.x it returned a set by default or, if the ordered parameter was True, it returned a list.

axis

Note

At version 2.x cf.Field.axis returns, by default, a cf.DomainAxis object. A domain axis identifier (such as “dim2”) may be returned by setting the key parameter to True.

>>> cf.__version__
2.0
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>
>>> f.axis('X')
<CF DomainAxis: 128>
>>> f.axis('X', key=True)
'dim2'

At version 1.x it always returned a domain axis identifier.

bounds

Warning

Running code written at version 1.x with the version 2.x library could produce scientifically different results.

Note

At version 2.x performing arithmetic on coordinates also modifies the coordinate bounds, if present.

>>> cf.__version__
2.0
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>
>>> t = f.coord('T')
>>> print t.array[0], t.bounds.array[0]
164569.0 [ 164554.  164584.]
>>> t -= 1000000
>>> print t.array[0], t.bounds.array[0]
-835431.0 [-835446. -835416.]

If the bounds are not to be changed, just the coordinate values, then the arithmetic may be applied to the coordinate object’s data array.

>>> t.data += 1000000
>>> print t.array[0], t.bounds.array[0]
164569.0 [-835446. -835416.]

At version 1.x performing arithmetic on coordinates did not modify the coordinate bounds - they had to be modified seperately.

collapse

Warning

Running code written at version 1.x with the version 2.x library could produce scientifically different results.

Note

At version 2.x cf.Field.collapse does not, by default, weight the calculations, i.e. the weights parameter defaults to None.

>>> cf.__version__
2.0
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>
>>> g = f.collapse('mean')
>>> g.datum()
279.1922
>>> g = f.collapse('mean', weights=None)
>>> g.datum()
279.1922

Non-equal weighting has to be specifically requested with the weights parameter.

>>> h = f.collapse('mean', axes=['X', 'Y', 'T'], weights=['T', 'area'])
>>> h.datum()
288.6733

At version 1.x the weights parameter defaulted to 'auto', meaning that calculations were were weighted according to metadata present in the field.

dump

Note

At version 2.x the output of cf.Field.dump has been reformatted.

FieldList

Warning

Running code written at version 1.x with the version 2.x library could produce scientifically different results.

Note

At version 2.x cf.FieldList is not a subclass of cf.Field, therefore cf.FieldList does not inherit any methods from cf.Field.

>>> cf.__version__
2.0
>>> fl
[<CF Field: specific_humidity(latitude(73), longitude(96)) K>,
 <CF Field: air_pressure(height(17), latitude(145), longitude(196)) K>]
>>> isinstance(fl, cf.Field)
False
>>> gl = fl.collapse('mean')
DeprecationError: collapse method has been removed from a field list. Use on individual fields.
>>> gl = cf.FieldList([f.collapse('mean') for f in fl])

At version 1.x cf.FieldList was a subclass of cf.Field and inherited all of the methods that returned a cf.Field when used on a field (such as collapse and squeeze).

read

Note

At version 2.x cf.read always returns a cf.FieldList.

>>> cf.__version__
2.0
>>> fl = cf.read('file[12].nc')
>>> fl
[<CF Field: specific_humidity(latitude(73), longitude(96)) K>,
 <CF Field: air_pressure(height(17), latitude(145), longitude(196)) K>]
>>> fl = cf.read('file3.nc')
>>> fl
[<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>]

The new function cf.read_field will always return a cf.Field if there is only one identified in the input file(s).

>>> f = cf.read_field('file3.nc')
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>

At version 1.x cf.read returned a cf.Field if only one field was found in the input files(s), otherwise it returned a cf.FieldList.

regridc

Note

At version 2.x cf.Field.regridc the regridding method must be specified. The method parameter does not have an 'auto' option.

>>> cf.__version__
2.0
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>
>>> g
<CF Field: specific_humidity(time(360), latitude(73), longitude(96)) K>
>>> h = f.regridc(g, 'time', 'nearest_stod')
>>> h
<CF Field: air_temperature(time(360), latitude(64), longitude(128)) K>

At version 1.x the regridding method defaulted to 'auto', meaning that the method was inferred according to metadata present in the field.

regrids

Note

At version 2.x cf.Field.regrids the regridding method must be specified. The method parameter does not have an 'auto' option.

>>> cf.__version__
2.0
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>
>>> g
<CF Field: specific_humidity(time(360), latitude(73), longitude(96)) K>
>>> h = f.regrids(g, 'conservative')
>>> h
<CF Field: air_temperature(time(12), latitude(73), longitude(96)) K>

At version 1.x the regridding method defaulted to 'auto', meaning that the method was inferred according to metadata present in the field.

properties

Note

At version 2.x cf.Field.properties is callable and allows the CF properties to be updated inplace.

>>> cf.__version__
2.0
>>> f.properties()
{'Conventions': 'CF-1.6',
 'experiment_id': 'pre-industrial control experiment',
 'project_id': 'IPCC Fourth Assessment',
 'realization': 1,
 'standard_name': 'air_temperature',
 'title': 'model output prepared for IPCC AR4'}

At version 1.x it wasn’t callable and returned a dict copy of the CF properties.

select

Note

At version 2.x cf.Field.select has been removed. Use cf.Field.match to see if an individual field meets given criteria.

>>> cf.__version__
2.0
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>
>>> f.match('air_temperature')
True

cf.FieldList.select always returns another field list.

>>> fl
[<CF Field: specific_humidity(latitude(73), longitude(96)) K>,
 <CF Field: air_pressure(height(17), latitude(145), longitude(196)) K>]
>>> fl.select('specific_humidity|air_pressure')
[<CF Field: specific_humidity(latitude(73), longitude(96)) K>,
 <CF Field: air_pressure(height(17), latitude(145), longitude(196)) K>]
>>> fl.select('specific_humidity')
[<CF Field: specific_humidity(latitude(73), longitude(96)) K>]
>>> fl.select('ocean_meridional_overturning_streamfunction')
[]

The new method cf.FieldList.select_field will always return a cf.Field if there is only one identified in the field list.

>>> fl.select_field('specific_humidity')
<CF Field: specific_humidity(latitude(73), longitude(96)) K>

At version 1.x cf.FieldList.select returned a cf.Field if only one field element was found in the field list, otherwise it returned a cf.FieldList. cf.Field.select either returned the field itself or an empty cf.FieldList.

Indexing a field

Warning

Running code written at version 1.x with the version 2.x library could produce scientifically different results.

Note

At version 2.x indexing on a field object returns a subspace of the field, in exactly the way that indexing the cf.Field.subspace attribute does.

>>> cf.__version__
2.0
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>
>>> g = f[::-2, 0, 28:]
>>> g
<CF Field: air_temperature(time(6), latitude(1), longitude(100)) K>
>>> h = f.subspace[::-2, 0, 28:]
>>> h
<CF Field: air_temperature(time(6), latitude(1), longitude(100)) K>
>>> g.equals(h)
True
>>> f.equals(f[0])
False

Assignment to a subspace of the data array may either be done to a subspace defined by direct indexing or to one defined by indexing the cf.Field.subspace attribute.

>>> g = f.copy()
>>> g[0] = -99
>>> h = f.copy()
>>> h.subspace[0] = -99
>>> g.equals(h)
True

At version 1.x direct indexing on a field returned the field itself, with no subspacing.

>>> cf.__version__
1.5
>>> f
<CF Field: air_temperature(time(12), latitude(64), longitude(128)) K>
>>> f.equals(f[0])
True