Source code for asdf.extension
# Licensed under a 3-clause BSD style license - see LICENSE.rst
# -*- coding: utf-8 -*-
import abc
import warnings
from pkg_resources import iter_entry_points
import six
import importlib
from . import asdftypes
from . import resolver
from .util import get_class_name
from .exceptions import AsdfDeprecationWarning
__all__ = ['AsdfExtension', 'AsdfExtensionList']
[docs]@six.add_metaclass(abc.ABCMeta)
class AsdfExtension(object):
"""
Abstract base class defining an extension to ASDF.
"""
@classmethod
def __subclasshook__(cls, C):
if cls is AsdfExtension:
return (hasattr(C, 'types') and
hasattr(C, 'tag_mapping') and
hasattr(C, 'url_mapping'))
return NotImplemented
@abc.abstractproperty
def types(self):
"""
A list of `asdf.CustomType` subclasses that describe how to store
custom objects to and from ASDF.
"""
pass
@abc.abstractproperty
def tag_mapping(self):
"""
A list of 2-tuples or callables mapping YAML tag prefixes to JSON Schema
URL prefixes.
For each entry:
- If a 2-tuple, the first part of the tuple is a YAML tag
prefix to match. The second part is a string, where case
the following are available as Python formatting tokens:
- ``{tag}``: the complete YAML tag.
- ``{tag_suffix}``: the part of the YAML tag after the
matched prefix.
- ``{tag_prefix}``: the matched YAML tag prefix.
- If a callable, it is passed the entire YAML tag must return
the entire JSON schema URL if it matches, otherwise, return `None`.
Note that while JSON Schema URLs uniquely define a JSON
Schema, they do not have to actually exist on an HTTP server
and be fetchable (much like XML namespaces).
For example, to match all YAML tags with the
``tag:nowhere.org:custom` prefix to the
``http://nowhere.org/schemas/custom/`` URL prefix::
return [('tag:nowhere.org:custom/',
'http://nowhere.org/schemas/custom/{tag_suffix}')]
"""
pass
@abc.abstractproperty
def url_mapping(self):
"""
A list of 2-tuples or callables mapping JSON Schema URLs to
other URLs. This is useful if the JSON Schemas are not
actually fetchable at their corresponding URLs but are on the
local filesystem, or, to save bandwidth, we have a copy of
fetchable schemas on the local filesystem. If neither is
desirable, it may simply be the empty list.
For each entry:
- If a 2-tuple, the first part is a URL prefix to match. The
second part is a string, where the following are available
as Python formatting tokens:
- ``{url}``: The entire JSON schema URL
- ``{url_prefix}``: The matched URL prefix
- ``{url_suffix}``: The part of the URL after the prefix.
- If a callable, it is passed the entire JSON Schema URL and
must return a resolvable URL pointing to the schema content.
If it doesn't match, should return `None`.
For example, to map a remote HTTP URL prefix to files installed
alongside as data alongside Python module::
return [('http://nowhere.org/schemas/custom/1.0.0/',
asdf.util.filepath_to_url(
os.path.join(SCHEMA_PATH, 'stsci.edu')) +
'/{url_suffix}.yaml'
)]
"""
pass
[docs]class AsdfExtensionList(object):
"""
Manage a set of extensions that are in effect.
"""
def __init__(self, extensions):
tag_mapping = []
url_mapping = []
validators = {}
self._type_index = asdftypes.AsdfTypeIndex()
for extension in extensions:
if not isinstance(extension, AsdfExtension):
raise TypeError(
"Extension must implement asdftypes.AsdfExtension "
"interface")
tag_mapping.extend(extension.tag_mapping)
url_mapping.extend(extension.url_mapping)
for typ in extension.types:
self._type_index.add_type(typ, extension)
validators.update(typ.validators)
for sibling in typ.versioned_siblings:
self._type_index.add_type(sibling, extension)
validators.update(sibling.validators)
self._tag_mapping = resolver.Resolver(tag_mapping, 'tag')
self._url_mapping = resolver.Resolver(url_mapping, 'url')
self._validators = validators
@property
def tag_to_schema_resolver(self):
"""Deprecated. Use `tag_mapping` instead"""
warnings.warn(
"The 'tag_to_schema_resolver' property is deprecated. Use "
"'tag_mapping' instead.",
AsdfDeprecationWarning)
return self._tag_mapping
@property
def tag_mapping(self):
return self._tag_mapping
@property
def url_mapping(self):
return self._url_mapping
@property
def type_index(self):
return self._type_index
@property
def validators(self):
return self._validators
class BuiltinExtension(object):
"""
This is the "extension" to ASDF that includes all the built-in
tags. Even though it's not really an extension and it's always
available, it's built in the same way as an extension.
"""
@property
def types(self):
return asdftypes._all_asdftypes
@property
def tag_mapping(self):
return resolver.DEFAULT_TAG_TO_URL_MAPPING
@property
def url_mapping(self):
return resolver.DEFAULT_URL_MAPPING
class _DefaultExtensions:
def __init__(self):
self._extensions = []
self._extension_list = None
self._package_metadata = {}
def _load_installed_extensions(self, group='asdf_extensions'):
self._extensions = []
for entry_point in iter_entry_points(group=group):
ext = entry_point.load()
if not issubclass(ext, AsdfExtension):
warnings.warn("Found entry point {}, from {} but it is not a "
"subclass of AsdfExtension, as expected. It is "
"being ignored.".format(ext, entry_point.dist))
continue
dist = entry_point.dist
name = get_class_name(ext, instance=False)
self._package_metadata[name] = (dist.project_name, dist.version)
self._extensions.append(ext())
@property
def extensions(self):
# This helps avoid a circular dependency with external packages
if not self._extensions:
self._load_installed_extensions()
return self._extensions
@property
def extension_list(self):
if self._extension_list is None:
self._extension_list = AsdfExtensionList(self.extensions)
return self._extension_list
@property
def package_metadata(self):
return self._package_metadata
default_extensions = _DefaultExtensions()