ExtensionType

class asdf.types.ExtensionType

Bases: object

The base class of all custom types in the tree.

Besides the attributes defined below, most subclasses will also override to_tree and from_tree.

Attributes Summary

handle_dynamic_subclasses
name
organization
requires
standard
supported_versions
types
validators
version
yaml_tag

Methods Summary

from_tree(tree, ctx)	Converts basic types representing YAML trees into custom types.
from_tree_tagged(tree, ctx)	Converts from tagged tree into custom type.
incompatible_version(version)	Indicates if given version is known to be incompatible with this type.
make_yaml_tag(name[, versioned])	Given the name of a type, returns a string representing its YAML tag.
names()	Returns the name(s) represented by this tag type as a list.
tag_base()	Returns the base of the YAML tag for types represented by this class.
to_tree(node, ctx)	Converts instances of custom types into YAML representations.
to_tree_tagged(node, ctx)	Converts instances of custom types into tagged objects.

Attributes Documentation

handle_dynamic_subclasses = False

name = None

organization = 'stsci.edu'

requires = []

standard = 'asdf'

supported_versions = {}

types = []

validators = {}

version = (1, 0, 0)

yaml_tag = None

Methods Documentation

classmethod from_tree(tree, ctx)

Converts basic types representing YAML trees into custom types.

This method should be overridden by custom extension classes in order to define how custom types are deserialized from the YAML representation back into their original types. Typically the method will return an instance of the original custom type. It is also permitted to return a generator, which yields a partially constructed result, then completes construction once the generator is drained. This is useful when constructing objects that contain reference cycles.

This method is called as part of the process of reading an ASDF file in order to construct an asdf.AsdfFile object. Whenever a YAML subtree is encountered that has a tag that corresponds to the yaml_tag property of this class, this method will be used to deserialize that tree back into an instance of the original custom type.

Parameters:

treeobject representing YAML tree

An instance of a basic Python type (possibly nested) that corresponds to a YAML subtree.

ctxasdf.AsdfFile

An instance of the asdf.AsdfFile object that is being constructed.

Returns:

An instance of the custom type represented by this extension class,

or a generator that yields that instance.

classmethod from_tree_tagged(tree, ctx)

Converts from tagged tree into custom type.

It is more common for extension classes to override from_tree instead of this method. This method should only be overridden if it is necessary to access the _tag property of the Tagged object directly.

Parameters:

treeasdf.tagged.Tagged object representing YAML tree

ctxasdf.AsdfFile

An instance of the asdf.AsdfFile object that is being constructed.

Returns:

An instance of the custom type represented by this extension class.

classmethod incompatible_version(version)

Indicates if given version is known to be incompatible with this type.

If this tag class explicitly identifies compatible versions then this checks whether a given version is compatible or not (see supported_versions). Otherwise, all versions are assumed to be compatible.

Child classes can override this method to affect how version compatibility for this type is determined.

Parameters:

versionstr or AsdfVersion

The version to test for compatibility.

classmethod make_yaml_tag(name, versioned=True)

Given the name of a type, returns a string representing its YAML tag.

Parameters:

namestr

The name of the type. In most cases this will correspond to the name attribute of the tag type. However, it is passed as a parameter since some tag types represent multiple custom types.

versionedbool

If True, the tag will be versioned. Otherwise, a YAML tag without a version will be returned.

Returns:

str representing the YAML tag

classmethod names()

Returns the name(s) represented by this tag type as a list.

While some tag types represent only a single custom type, others represent multiple types. In the latter case, the name attribute of the extension is actually a list, not simply a string. This method normalizes the value of name by returning a list in all cases.

Returns:

list of names represented by this tag type

classmethod tag_base()

Returns the base of the YAML tag for types represented by this class.

This method returns the portion of the tag that represents the standard and the organization of any type represented by this class.

Returns:

str representing the base of the YAML tag

classmethod to_tree(node, ctx)

Converts instances of custom types into YAML representations.

This method should be overridden by custom extension classes in order to define how custom types are serialized into YAML. The method must return a single Python object corresponding to one of the basic YAML types (dict, list, str, or number). However, the types can be nested and combined in order to represent more complex custom types.

This method is called as part of the process of writing an asdf.AsdfFile object. Whenever a custom type (or a subclass of that type) that is listed in the types attribute of this class is encountered, this method will be used to serialize that type.

The name to_tree refers to the act of converting a custom type into part of a YAML object tree.

Parameters:

nodeobject

Instance of a custom type to be serialized. Will be an instance (or an instance of a subclass) of one of the types listed in the types attribute of this class.

ctxasdf.AsdfFile

An instance of the asdf.AsdfFile object that is being written out.

Returns:

A basic YAML type (dict, list, str, int, float, or

complex) representing the properties of the custom type to be

serialized. These types can be nested in order to represent more

complex custom types.

classmethod to_tree_tagged(node, ctx)

Converts instances of custom types into tagged objects.

It is more common for custom tag types to override to_tree instead of this method. This method should be overridden if it is necessary to modify the YAML tag that will be used to tag this object.

Parameters:

nodeobject

Instance of a custom type to be serialized. Will be an instance (or an instance of a subclass) of one of the types listed in the types attribute of this class.

ctxasdf.AsdfFile

An instance of the asdf.AsdfFile object that is being written out.

Returns:

An instance of asdf.tagged.Tagged.