Meta

class Meta(*args, **kwargs)

The Meta structure should be included as the first member of a Buffer metadata structure. The structure defines the API of the metadata and should be accessible to all elements using the metadata.

A metadata API is registered with api_type_register() which takes a name for the metadata API and some tags associated with the metadata. With api_type_has_tag() one can check if a certain metadata API contains a given tag.

Multiple implementations of a metadata API can be registered. To implement a metadata API, register() should be used. This function takes all parameters needed to create, free and transform metadata along with the size of the metadata. The function returns a MetaInfo structure that contains the information for the implementation of the API.

A specific implementation can be retrieved by name with get_info().

See Buffer for how the metadata can be added, retrieved and removed from buffers.

Methods

class Meta
api_type_get_tags(api: type) → list[str]

Added in version 1.2.

Parameters:

api – an API

api_type_has_tag(api: type, tag: int) → bool

Check if api was registered with tag.

Parameters:

  • api – an API

  • tag – the tag to check

api_type_register(api: str, tags: Sequence[str]) → type

Register and return a GType for the api and associate it with tags.

Parameters:

  • api – an API to register

  • tags – tags for api

compare_seqnum(meta2: Meta) → int

Meta sequence number compare function. Can be used as CompareFunc or a CompareDataFunc.

Added in version 1.16.

Parameters:

meta2 – a Meta

get_info(impl: str) → MetaInfo | None

Lookup a previously registered meta info structure by its implementation name impl.

Parameters:

impl – the name

get_seqnum() → int

Gets seqnum for this meta.

Added in version 1.16.

register(api: type, impl: str, size: int, init_func: Callable[[Meta, None, Buffer], bool], free_func: Callable[[Meta, Buffer], None], transform_func: Callable[[Buffer, Meta, Buffer, int, None], bool]) → MetaInfo

Register a new Meta implementation.

The same info can be retrieved later with get_info() by using impl as the key.

Parameters:

  • api – the type of the Meta API

  • impl – the name of the Meta implementation

  • size – the size of the Meta structure

  • init_func – a MetaInitFunction

  • free_func – a MetaFreeFunction

  • transform_func – a MetaTransformFunction

register_custom(name: str, tags: Sequence[str], transform_func: Callable[[...], bool] | None = None, *user_data: Any) → MetaInfo

Register a new custom Meta implementation, backed by an opaque structure holding a Structure.

The registered info can be retrieved later with get_info() by using name as the key.

The backing Structure can be retrieved with get_structure(), its mutability is conditioned by the writability of the buffer the meta is attached to.

When transform_func is None, the meta and its backing Structure will always be copied when the transform operation is copy, other operations are discarded, copy regions are ignored.

Added in version 1.20.

Parameters:

  • name – the name of the Meta implementation

  • tags – tags for api

  • transform_func – a MetaTransformFunction

  • user_data – user data passed to transform_func

Fields

class Meta
flags

Extra flags for the metadata

info

Pointer to the MetaInfo