Source code for franz.openrdf.model.statement

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# pylint: disable-msg=C0103 

################################################################################
# Copyright (c) 2006-2017 Franz Inc.  
# All rights reserved. This program and the accompanying materials are
# made available under the terms of the MIT License which accompanies
# this distribution, and is available at http://opensource.org/licenses/MIT
################################################################################

from __future__ import absolute_import
from __future__ import unicode_literals
from past.builtins import basestring
from future.utils import python_2_unicode_compatible

from franz.openrdf.model.utils import parse_term
from .value import Value, URI


@python_2_unicode_compatible
class Statement(object):
    """
    Wraps a triple or a quad. Might also contain an id.
    """
    __slots__ = ('subject', 'predicate', 'object', 'context', 'id', '_hash')

    def __init__(self, subject, predicate, object, context=None, id=None):
        """
        Create a statement.

        Each component can be either a Value object or a string in N-Triples format.
        Strings will be parsed lazily the first time a component is accessed.
        Accessors will always return Value objects.

        :param subject: Subject component - URI, blank node or a string
                        in N-Triples format.
        :type subject: URI|BNode|str
        :param predicate: Predicate component. Either a URI or a string
                          in N-Triples format.
        :type predicate: URI|str
        :param object: Subject component. Either a Value or a string
                       in N-Triples format.
        :type object: Value|str
        :param context: Graph component (optional). Can be a URI or
                        a string in N-Triples format.
        :type context: URI|str
        :param id: Statement id (optional).
        :type id: int|str
        """
        self.subject = subject
        self.predicate = predicate
        self.object = object
        self.context = context
        self.id = id
        self._hash = None

    def __eq__(self, other):
        if not isinstance(other, Statement):
            return NotImplemented

        # The object is potentially the cheapest to check, as types
        # of these references might be different.
        # In general the number of different predicates in sets of
        # statements is the smallest, so predicate equality is checked
        # last.
        if self.getObject() == other.getObject() and self.getSubject() == other.getSubject() \
                and self.getPredicate() == other.getPredicate():
            if self.context:
                return self.getContext() == other.getContext()
            else:
                return not other.getContext()
        else:
            return False

    def __hash__(self):
        if self._hash is None:
            self._hash = hash((self.getSubject(), self.getPredicate(), self.getObject(), self.getContext()))
        return self._hash

    def __str__(self):
        elements = [self.getSubject(), self.getPredicate(), self.getObject(), self.getContext(), self.getTripleID()]
        while len(elements) > 3 and elements[-1] is None:
            elements.pop()
        return '(' + ', '.join(map(str, elements)) + ')'

    def __len__(self):
        return 3 if self.context is None else 4

    def __getitem__(self, index):
        if index == 0: return self.getSubject()
        elif index == 1: return self.getPredicate()
        elif index == 2: return self.getObject()
        elif index == 3: return self.getContext()
        else:
            raise IndexError('Illegal index (%d), must be < 4' % index)

    def getSubject(self):
        """
        Get the subject (the first element of the statement).

        :return: Subject.
        :rtype: Value
        """
        # Lazily parse and replace the value if needed.
        if isinstance(self.subject, basestring):
            self.subject = parse_term(self.subject)
        return self.subject
    
    def setSubject(self, subject):
        self.subject = subject
    
    def getPredicate(self):
        """
        Get the predicate (the second element of the statement).

        :return: Predicate.
        :rtype: URI
        """
        # Lazily parse and replace the value if needed.
        if isinstance(self.predicate, basestring):
            self.predicate = parse_term(self.predicate)
        return self.predicate
     
    def setPredicate(self, predicate):
        self.predicate = predicate
    
    def getObject(self):
        """
        Get the object (the third element of the statement).

        :return: Object.
        :rtype: Value
        """
        # Lazily parse and replace the value if needed.
        if isinstance(self.object, basestring):
            self.object = parse_term(self.object)
        return self.object
    
    def setObject(self, object):
        self.object = object
    
    def getContext(self):
        """
        Get the graph (the fourth, optional element of the statement).

        :return: Graph URI.
        :rtype: URI
        """
        # Lazily parse and replace the value if needed.
        if isinstance(self.context, basestring):
            self.context = parse_term(self.context)
        return self.context
    
    def setContext(self, context):
        self.context = context

    def getTripleID(self):
        """
        Get the statement id.

        Note that this field might not present, depending on the way in which
        the statement has been created.

        :return: A numerical id.
        :rtype: int
        """
        # Lazily parse and replace the value if needed.
        if isinstance(self.id, basestring):
            self.id = int(self.id)
        return self.id