"""
Support for Converter, the new API for serializing custom
types. Will eventually replace the `asdf.types` module.
"""
import abc
from ..util import get_class_name, uri_match
[docs]class Converter(abc.ABC):
"""
Abstract base class for plugins that convert nodes from the
parsed YAML tree into custom objects, and vice versa.
Implementing classes must provide the `tags` and `types`
properties and `to_yaml_tree` and `from_yaml_tree` methods.
The `select_tag` method is optional.
"""
@classmethod
def __subclasshook__(cls, C):
if cls is Converter:
return (
hasattr(C, "tags")
and hasattr(C, "types")
and hasattr(C, "to_yaml_tree")
and hasattr(C, "from_yaml_tree")
)
return NotImplemented # pragma: no cover
@property
@abc.abstractmethod
def tags(self):
"""
Get the YAML tags that this converter is capable of
handling. URI patterns are permitted, see
`asdf.util.uri_match` for details.
Returns
-------
iterable of str
Tag URIs or URI patterns.
"""
pass # pragma: no cover
@property
@abc.abstractmethod
def types(self):
"""
Get the Python types that this converter is capable of
handling.
Returns
-------
iterable of str or type
If str, the fully qualified class name of the type.
"""
pass # pragma: no cover
[docs] def select_tag(self, obj, tags, ctx):
"""
Select the tag to use when converting an object to YAML.
Typically only one tag will be active in a given context, but
converters that map one type to many tags must provide logic
to choose the appropriate tag.
Parameters
----------
obj : object
Instance of the custom type being converted. Guaranteed
to be an instance of one of the types listed in the
`types` property.
tags : list of str
List of active tags to choose from. Guaranteed to match
one of the tag patterns listed in the 'tags' property.
ctx : asdf.asdf.SerializationContext
Context of the current serialization request.
Returns
-------
str
The selected tag. Should be one of the tags passed
to this method in the `tags` parameter.
"""
return tags[0]
[docs] @abc.abstractmethod
def to_yaml_tree(self, obj, tag, ctx):
"""
Convert an object into a node suitable for YAML serialization.
This method is not responsible for writing actual YAML; rather, it
converts an instance of a custom type to a built-in Python object type
(such as dict, list, str, or number), which can then be automatically
serialized to YAML as needed.
For container types returned by this method (dict or list),
the children of the container need not themselves be converted.
Any list elements or dict values will be converted by subsequent
calls to to_yaml_tree implementations.
The returned node must be an instance of `dict`, `list`, or `str`.
Children may be any type supported by an available Converter.
Parameters
----------
obj : object
Instance of a custom type to be serialized. Guaranteed to
be an instance of one of the types listed in the `types`
property.
tag : str
The tag identifying the YAML type that ``obj`` should be
converted into. Selected by a call to this converter's
select_tag method.
ctx : asdf.asdf.SerializationContext
The context of the current serialization request.
Returns
-------
dict or list or str
The YAML node representation of the object.
"""
pass # pragma: no cover
[docs] @abc.abstractmethod
def from_yaml_tree(self, node, tag, ctx):
"""
Convert a YAML node into an instance of a custom type.
For container types received by this method (dict or list),
the children of the container will have already been converted
by prior calls to from_yaml_tree implementations.
Note on circular references: trees that reference themselves
among their descendants must be handled with care. Most
implementations need not concern themselves with this case, but
if the custom type supports circular references, then the
implementation of this method will need to return a generator.
Consult the documentation for more details.
Parameters
----------
node : dict or list or str
The YAML node to convert.
tag : str
The YAML tag of the object being converted.
ctx : asdf.asdf.SerializationContext
The context of the current deserialization request.
Returns
-------
object
An instance of one of the types listed in the `types` property,
or a generator that yields such an instance.
"""
pass # pragma: no cover
[docs]class ConverterProxy(Converter):
"""
Proxy that wraps a `Converter` and provides default
implementations of optional methods.
"""
def __init__(self, delegate, extension):
if not isinstance(delegate, Converter):
raise TypeError("Converter must implement the asdf.extension.Converter interface")
self._delegate = delegate
self._extension = extension
self._class_name = get_class_name(delegate)
# Sort these out up-front so that errors are raised when the extension is loaded
# and not in the middle of the user's session. The extension will fail to load
# and a warning will be emitted, but it won't crash the program.
relevant_tags = set()
for tag in delegate.tags:
if isinstance(tag, str):
relevant_tags.update(t.tag_uri for t in extension.tags if uri_match(tag, t.tag_uri))
else:
raise TypeError("Converter property 'tags' must contain str values")
if len(relevant_tags) > 1 and not hasattr(delegate, "select_tag"):
raise RuntimeError(
"Converter handles multiple tags for this extension, but does not implement a select_tag method."
)
self._tags = sorted(relevant_tags)
self._types = []
for typ in delegate.types:
if isinstance(typ, (str, type)):
self._types.append(typ)
else:
raise TypeError("Converter property 'types' must contain str or type values")
@property
def tags(self):
"""
Get the list of tag URIs that this converter is capable of
handling.
Returns
-------
list of str
"""
return self._tags
@property
def types(self):
"""
Get the Python types that this converter is capable of
handling.
Returns
-------
list of type or str
"""
return self._types
[docs] def select_tag(self, obj, ctx):
"""
Select the tag to use when converting an object to YAML.
Parameters
----------
obj : object
Instance of the custom type being converted.
ctx : asdf.asdf.SerializationContext
Serialization parameters.
Returns
-------
str
Selected tag.
"""
method = getattr(self._delegate, "select_tag", None)
if method is None:
return self._tags[0]
else:
return method(obj, self._tags, ctx)
[docs] def to_yaml_tree(self, obj, tag, ctx):
"""
Convert an object into a node suitable for YAML serialization.
Parameters
----------
obj : object
Instance of a custom type to be serialized.
tag : str
The tag identifying the YAML type that ``obj`` should be
converted into.
ctx : asdf.asdf.SerializationContext
Serialization parameters.
Returns
-------
object
The YAML node representation of the object.
"""
return self._delegate.to_yaml_tree(obj, tag, ctx)
[docs] def from_yaml_tree(self, node, tag, ctx):
"""
Convert a YAML node into an instance of a custom type.
Parameters
----------
tree : dict or list or str
The YAML node to convert.
tag : str
The YAML tag of the object being converted.
ctx : asdf.asdf.SerializationContext
Serialization parameters.
Returns
-------
object
"""
return self._delegate.from_yaml_tree(node, tag, ctx)
@property
def delegate(self):
"""
Get the wrapped converter instance.
Returns
-------
asdf.extension.Converter
"""
return self._delegate
@property
def extension(self):
"""
Get the extension that provided this converter.
Returns
-------
asdf.extension.ExtensionProxy
"""
return self._extension
@property
def package_name(self):
"""
Get the name of the Python package of this converter's
extension. This may not be the same package that implements
the converter's class.
Returns
-------
str or None
Package name, or `None` if the extension was added at runtime.
"""
return self.extension.package_name
@property
def package_version(self):
"""
Get the version of the Python package of this converter's
extension. This may not be the same package that implements
the converter's class.
Returns
-------
str or None
Package version, or `None` if the extension was added at runtime.
"""
return self.extension.package_version
@property
def class_name(self):
"""
Get the fully qualified class name of this converter.
Returns
-------
str
"""
return self._class_name
def __eq__(self, other):
if isinstance(other, ConverterProxy):
return other.delegate is self.delegate and other.extension is self.extension
else:
return False
def __hash__(self):
return hash((id(self.delegate), id(self.extension)))
def __repr__(self):
if self.package_name is None:
package_description = "(none)"
else:
package_description = f"{self.package_name}=={self.package_version}"
return f"<ConverterProxy class: {self.class_name} package: {package_description}>"