Metadata

Metadata objects are the basic unit of metadata storage.

class emdfile.classes.Metadata(name: str | None = 'metadata', data: dict | None = None)

A Metadata instance holds an arbitrary collection of metadata items, nested to any depth. Nodes may contain arbitrarily many Metadata instances, accessible through their .metadata propery.

Metadata Instances

Calling

>>> md = Metadata()
>>> md['param'] = value
>>> v = meta['param']

creates a metadata instance, assigns a value to a key, and retrieves it, and

>>> md = Metadata(
>>>     name='md1',
>>>     data={'x':1,'y':2}
>>> )

creates a named Metadata instance already containing some items, and

>>> md2 = Metadata(
>>>     'm2',
>>>     {
>>>         'a' : 1,
>>>         'b' : {
>>>             'c' : 2,
>>>             'd' : 3
>>>         }
>>>     }

creates an instance with nesting. Values may take on datatypes including

• numbers

• strings

• arrays

• bools

• dicts

• None

• tuples

  • empty

  • of numbers

  • of tuples

  • of arrays

  • of strings

• lists

  • empty

  • of numbers

  • of arrays

  • of strings

Metadata instances include a

>>> md.copy
>>> md.keys

method and attribute, respectively.

Nodes and Metadata

Each Node instance may contain arbitrarily many Metadata instances. These are accesed with

>>> node.metadata

which, when called as above, returns a dictionary of all contained Metadata instances. New Metadata instances are added by assignement, so

>>> node.metadata = Metadata('md1',{'x':1,'y':2})
>>> node.metadata = Metadata('md2',{'a':1,'b':{'c':2,'d':3}})

will add both the ‘md1’ and ‘md2’ instances to the node, and

>>> node.metadata['md1']

will subsequently return Metadata instance ‘md1’. When saved to an HDF5 file, all the metadata instances returned by a node’s .metadata property are saved to that nodes metadatabundle group.

__init__(name: str | None = 'metadata', data: dict | None = None)

Parameters:

name (string)

copy(name=None)

classmethod from_h5(group)

Accepts an h5py Group which is open in read mode, confirms that it represents an EMD MetadataDict group, then loads and returns it as a Metadata instance.

Parameters:

group (HDF5 group)

Return type:

(Metadata)

to_h5(group)

Accepts an h5py Group which is open in write or append mode. Writes a new group with this object’s name and saves its metadata in it.

Parameters:

group (h5py Group)