Field.domain_axis(identity, key=False, default=ValueError())[source]

Return a domain axis construct, or its key.

New in version 3.0.0.


Select the domain axis construct by one of:

  • An identity or key of a 1-d coordinate construct that whose data spans the domain axis construct.
  • A domain axis construct identity or key.
  • The position of the domain axis construct in the field construct’s data.

A construct identity is specified by a string (e.g. 'latitude', 'long_name=time', 'ncvar%lat', etc.); or a compiled regular expression (e.g. re.compile('^atmosphere')) that selects the relevant constructs whose identities match via

Each construct has a number of identities, and is selected if any of them match any of those provided. A construct’s identities are those returned by its identities method. In the following example, the construct x has six identities:

>>> x.identities()
['time', 'long_name=Time', 'foo=bar', 'standard_name=time', 'ncvar%t', 'T']

A construct key may optionally have the 'key%' prefix. For example 'dimensioncoordinate2' and 'key%dimensioncoordinate2' are both acceptable keys.

A position of a domain axis construct in the field construct’s data is specified by an integer index.

Note that in the output of a print call or dump method, a construct is always described by one of its identities, and so this description may always be used as an identity argument.

Parameter example:


Parameter example:


Parameter example:


Parameter example:


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key: `bool, optional

If True then return the selected construct key. By default the construct itself is returned.

default: optional

Return the value of the default parameter if a construct can not be found. If set to an Exception instance then it will be raised instead.

DomainAxis or str

The selected domain axis construct, or its key.