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context.py
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/
context.py
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# -*- coding: utf-8 -*-
"""
Implementation of the JSON-LD Context structure. See:
http://json-ld.org/
"""
from rdflib.namespace import RDF
from .keys import (BASE, CONTAINER, CONTEXT, GRAPH, ID, INDEX, LANG, LIST,
REV, SET, TYPE, VALUE, VOCAB)
from . import errors
from .util import source_to_json, urljoin, urlsplit, split_iri, norm_url
NODE_KEYS = set([LANG, ID, TYPE, VALUE, LIST, SET, REV, GRAPH])
class Defined(int): pass
UNDEF = Defined(0)
class Context(object):
def __init__(self, source=None, base=None):
self.language = None
self.vocab = None
self.base = base
self.doc_base = base
self.terms = {}
self._alias = {}
self._lookup = {}
self._prefixes = {}
self.active = False
if source:
self.load(source)
@property
def base(self):
return self._base
@base.setter
def base(self, base):
if base:
hash_index = base.find('#')
if hash_index > -1:
base = base[0:hash_index]
self._base = base
self._basedomain = '%s://%s' % urlsplit(base)[0:2] if base else None
def subcontext(self, source):
# IMPROVE: to optimize, implement SubContext with parent fallback support
ctx = Context()
ctx.language = self.language
ctx.vocab = self.vocab
ctx.base = self.base
ctx.doc_base = self.doc_base
ctx._alias = self._alias.copy()
ctx.terms = self.terms.copy()
ctx._lookup = self._lookup.copy()
ctx._prefixes = self._prefixes.copy()
ctx.load(source)
return ctx
def get_id(self, obj):
return self._get(obj, ID)
def get_type(self, obj):
return self._get(obj, TYPE)
def get_language(self, obj):
return self._get(obj, LANG)
def get_value(self, obj):
return self._get(obj, VALUE)
def get_graph(self, obj):
return self._get(obj, GRAPH)
def get_list(self, obj):
return self._get(obj, LIST)
def get_set(self, obj):
return self._get(obj, SET)
def get_rev(self, obj):
return self._get(obj, REV)
def _get(self, obj, key):
return obj.get(self._alias.get(key)) or obj.get(key)
def get_key(self, key):
return self._alias.get(key, key)
lang_key = property(lambda self: self.get_key(LANG))
id_key = property(lambda self: self.get_key(ID))
type_key = property(lambda self: self.get_key(TYPE))
value_key = property(lambda self: self.get_key(VALUE))
list_key = property(lambda self: self.get_key(LIST))
rev_key = property(lambda self: self.get_key(REV))
graph_key = property(lambda self: self.get_key(GRAPH))
def add_term(self, name, idref, coercion=UNDEF, container=UNDEF,
language=UNDEF, reverse=False):
term = Term(idref, name, coercion, container, language, reverse)
self.terms[name] = term
self._lookup[(idref, coercion or language, container, reverse)] = term
self._prefixes[idref] = name
def find_term(self, idref, coercion=None, container=UNDEF,
language=None, reverse=False):
lu = self._lookup
if coercion is None:
coercion = language
if coercion is not UNDEF and container:
found = lu.get((idref, coercion, container, reverse))
if found: return found
if coercion is not UNDEF:
found = lu.get((idref, coercion, UNDEF, reverse))
if found: return found
if container:
found = lu.get((idref, coercion, container, reverse))
if found: return found
elif language:
found = lu.get((idref, UNDEF, LANG, reverse))
if found: return found
else:
found = lu.get((idref, coercion or UNDEF, SET, reverse))
if found: return found
return lu.get((idref, UNDEF, UNDEF, reverse))
def resolve(self, curie_or_iri):
iri = self.expand(curie_or_iri, False)
if self.isblank(iri):
return iri
return self.resolve_iri(iri)
def resolve_iri(self, iri):
return norm_url(self._base, iri)
def isblank(self, ref):
return ref.startswith('_:')
def expand(self, term_curie_or_iri, use_vocab=True):
if use_vocab:
term = self.terms.get(term_curie_or_iri)
if term:
return term.id
is_term, pfx, local = self._prep_expand(term_curie_or_iri)
if pfx == '_':
return term_curie_or_iri
if pfx is not None:
ns = self.terms.get(pfx)
if ns and ns.id:
return ns.id + local
elif is_term and use_vocab:
if self.vocab:
return self.vocab + term_curie_or_iri
return None
return self.resolve_iri(term_curie_or_iri)
def shrink_iri(self, iri):
ns, name = split_iri(unicode(iri))
pfx = self._prefixes.get(ns)
if pfx:
return u":".join((pfx, name))
elif self._base:
if unicode(iri) == self._base:
return ""
elif iri.startswith(self._basedomain):
return iri[len(self._basedomain):]
return iri
def to_symbol(self, iri):
iri = unicode(iri)
term = self.find_term(iri)
if term:
return term.name
ns, name = split_iri(iri)
if ns == self.vocab:
return name
pfx = self._prefixes.get(ns)
if pfx:
return u":".join((pfx, name))
return iri
def load(self, source, base=None):
self.active = True
sources = []
source = source if isinstance(source, list) else [source]
self._prep_sources(base, source, sources)
for source_url, source in sources:
self._read_source(source, source_url)
def _prep_sources(self, base, inputs, sources, referenced_contexts=None,
in_source_url=None):
referenced_contexts = referenced_contexts or set()
for source in inputs:
if isinstance(source, basestring):
source_url = urljoin(base, source)
if source_url in referenced_contexts:
raise errors.RECURSIVE_CONTEXT_INCLUSION
referenced_contexts.add(source_url)
source = source_to_json(source_url)
if CONTEXT not in source:
raise errors.INVALID_REMOTE_CONTEXT
else:
source_url = in_source_url
if isinstance(source, dict):
if CONTEXT in source:
source = source[CONTEXT]
source = source if isinstance(source, list) else [source]
if isinstance(source, list):
self._prep_sources(base, source, sources, referenced_contexts, source_url)
else:
sources.append((source_url, source))
def _read_source(self, source, source_url=None):
self.vocab = source.get(VOCAB, self.vocab)
for key, value in source.items():
if key == LANG:
self.language = value
elif key == VOCAB:
continue
elif key == BASE:
if source_url:
continue
self.base = value
else:
self._read_term(source, key, value)
def _read_term(self, source, name, dfn):
if isinstance(dfn, dict):
#term = self._create_term(source, key, value)
rev = dfn.get(REV)
idref = rev or dfn.get(ID, UNDEF)
if idref == TYPE:
idref = unicode(RDF.type)
elif idref is not UNDEF:
idref = self._rec_expand(source, idref)
elif ':' in name:
idref = self._rec_expand(source, name)
elif self.vocab:
idref = self.vocab + name
coercion = dfn.get(TYPE, UNDEF)
if coercion and coercion not in (ID, TYPE, VOCAB):
coercion = self._rec_expand(source, coercion)
self.add_term(name, idref, coercion,
dfn.get(CONTAINER, UNDEF), dfn.get(LANG, UNDEF), bool(rev))
else:
idref = self._rec_expand(source, dfn)
self.add_term(name, idref)
if idref in NODE_KEYS:
self._alias[idref] = name
def _rec_expand(self, source, expr, prev=None):
if expr == prev or expr in NODE_KEYS:
return expr
is_term, pfx, nxt = self._prep_expand(expr)
if pfx:
iri = self._get_source_id(source, pfx) or self.expand(pfx)
if iri is None:
nxt = expr
else:
nxt = iri + nxt
else:
nxt = self._get_source_id(source, nxt) or nxt
if ':' not in nxt and self.vocab:
return self.vocab + nxt
return self._rec_expand(source, nxt, expr)
def _prep_expand(self, expr):
if ':' not in expr:
return True, None, expr
pfx, local = expr.split(':', 1)
if not local.startswith('//'):
return False, pfx, local
else:
return False, None, expr
def _get_source_id(self, source, key):
# .. from source dict or if already defined
term = source.get(key)
if term is None:
dfn = self.terms.get(key)
if dfn:
term = dfn.id
elif isinstance(term, dict):
term = term.get(ID)
return term
class Term(object):
def __init__(self, idref, name, coercion=UNDEF, container=UNDEF,
language=UNDEF, reverse=False):
self.name = name
self.id = idref
self.type = coercion
self.container = container
self.language = language
self.reverse = reverse