MetaData#

class astropy.utils.metadata.MetaData(doc='', copy=True, *, default_factory=<class 'collections.OrderedDict'>)[source]#

Bases: object

A descriptor for classes that have a meta property.

This can be set to any valid Mapping.

Parameters:

docstr, optional: Documentation for the attribute of the class. Default is "".

Added in version 1.2.
copybool, optional: If True the value is deepcopied before setting, otherwise it is saved as reference. Default is True.

Added in version 1.2.
default_factoryCallable[[], Mapping], optional keyword-only: The factory to use to create the default value of the meta attribute. This must be a callable that returns a Mapping object. Default is OrderedDict, creating an empty OrderedDict.

Added in version 6.0.

Examples

MetaData can be used as a descriptor to define a meta attribute`.

>>> class Foo:
...     meta = MetaData()
...     def __init__(self, meta=None):
...         self.meta = meta

Foo can be instantiated with a meta argument.

>>> foo = Foo(meta={'a': 1, 'b': 2})
>>> foo.meta
{'a': 1, 'b': 2}

The default value of meta is an empty OrderedDict. This can be set by passing None to the meta argument.

>>> foo = Foo()
>>> foo.meta
OrderedDict()

If an OrderedDict is not a good default metadata type then the default_factory keyword can be used to set the default to a different Mapping type, when the class is defined.’

>>> class Bar:
...     meta = MetaData(default_factory=dict)
...     def __init__(self, meta=None):
...         self.meta = meta

>>> Bar().meta
{}

When accessed from the class .meta returns None since metadata is on the class’ instances, not the class itself.

>>> print(Foo.meta)
None

Attributes Summary

default_factory

Attributes Documentation

default_factory#