Source code for asdf.extension._converter

"""
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 "<ConverterProxy class: {} package: {}>".format( self.class_name, package_description, )