python-sparqlwrapper 1.4.1-2 / usr / share / pyshared / SPARQLWrapper / SmartWrapper.py

# -*- coding: utf-8 -*-

"""
@see: U{SPARQL Specification<http://www.w3.org/TR/rdf-sparql-query/>}
@authors: U{Ivan Herman<http://www.ivan-herman.net>}, U{Sergio Fernández<http://www.wikier.org>}, U{Carlos Tejo Alonso<http://www.dayures.net>}
@organization: U{World Wide Web Consortium<http://www.w3.org>} and U{Foundation CTIC<http://www.fundacionctic.org/>}.
@license: U{W3C® SOFTWARE NOTICE AND LICENSE<href="http://www.w3.org/Consortium/Legal/copyright-software">}
@requires: U{RDFLib<http://rdflib.net>} package.
"""

import SPARQLWrapper
from SPARQLWrapper.Wrapper import JSON, SELECT
import urllib2
from types import *


######################################################################################

class Value :
	"""
	Class encapsulating a single binding for a variable.

	@cvar URI: the string denoting a URI variable
	@cvar Literal: the string denoting a Literal variable
	@cvar TypedLiteral: the string denoting a typed literal variable
	@cvar BNODE: the string denoting a blank node variable

	@ivar variable: The original variable, stored for an easier reference
	@type variable: string
	@ivar value: Value of the binding
	@type value: string
	@ivar type: Type of the binding
	@type type: string; one of  L{Value.URI}, L{Value.Literal}, L{Value.TypedLiteral}, or L{Value.BNODE}
	@ivar lang: Language tag of the binding, or C{None} if not set
	@type lang: string
	@ivar datatype: Datatype of the binding, or C{None} if not set
	@type datatype: string (URI)
	"""
	URI          = "uri"
	Literal      = "literal"
	TypedLiteral = "typed-literal"
	BNODE        = "bnode"

	def __init__(self,variable,binding) :
		"""
		@param variable: the variable for that binding. Stored for an easier reference
		@param binding: the binding dictionary part of the return result for a specific binding
		"""
		self.variable  = variable
		self.value     = binding['value']
		self.type      = binding['type']
		self.lang      = None
		self.datatype  = None
		try :
			self.lang = binding['xml:lang']
		except :
			# no lang is set
			pass
		try :
			self.datatype = binding['datatype']
		except :
			pass

######################################################################################

class Bindings :
	"""
	Class encapsulating one query result, based on the JSON return format. It decodes the
	return values to make it a bit more usable for a standard usage. The class consumes the
	return value and instantiates a number of attributes that can be consulted directly. See
	the list of variables.

	The U{Serializing SPARQL Query Results in JSON<http://www.w3.org/TR/rdf-sparql-json-res/>} explains the details of the
	JSON return structures. Very succintly: the return data has "bindings", which means a list of dictionaries. Each
	dictionary is a possible binding of the SELECT variables to L{Value} instances. This structure is made a bit
	more usable by this class.

	@ivar fullResult: The original dictionary of the results, stored for an easier reference
	@ivar head: Header part of the return, see the JSON return format document for details
	@ivar variables: List of unbounds (variables) of the original query. It is an array of strings. None in the case of an ASK query
	@ivar bindings: The final bindings: array of dictionaries, mapping variables to L{Value} instances.
	(If unbound, then no value is set in the dictionary; that can be easily checked with
	C{var in res.bindings[..]}, for example.)
	@ivar askResult: by default, set to False; in case of an ASK query, the result of the query
	@type askResult: Boolean
	"""
	def __init__(self,retval) :
		"""
		@param retval: the query result, instance of a L{Wrapper.QueryResult}
		"""
		self.fullResult  = retval._convertJSON()
		self.head        = self.fullResult['head']
		self.variables   = None
		try :
			self.variables   = self.fullResult['head']['vars']
		except :
			pass

		self.bindings    = []
		try :
			for b in self.fullResult['results']['bindings'] :
				#  this is a single binding.  It is a dictionary per variable; each value is a dictionary again that has to be
				# converted into a Value instance
				newBind = {}
				for key in self.variables :
					if key in b :
						# there is a real binding for this key
						newBind[key] = Value(key,b[key])
				self.bindings.append(newBind)
		except :
			pass

		self.askResult = False
		try :
			self.askResult = self.fullResult["boolean"]
		except :
			pass

	def getValues(self,key) :
		"""A shorthand for the retrieval of all bindings for a single key. It is
		equivalent to "C{[b[key] for b in self[key]]}"
		@param key: possible variable
		@return: list of L{Value} instances
		"""
		try :
			return [b[key] for b in self[key]]
		except :
			return []

	def __contains__(self,key) :
		"""Emulation of the "C{key in obj}" operator. Key can be a string for a variable or an array/tuple
		of strings.

		If C{key} is a variable, the return value is C{True} if there is at least one binding where C{key} is
		bound. If C{key} is an array or tuple, the return value is C{True} if there is at least one binding
		where I{all} variables in C{key} are bound.

		@param key: possible variable, or array/tuple of variables
		@return: whether there is a binding of the variable in the return
		@rtype: Boolean
		"""
		if len(self.bindings) == 0 : return False
		if type(key) is ListType or type(key) is TupleType :
			# check first whether they are all really variables
			if False in [ k in self.variables for k in key ]: return False
			for b in self.bindings :
				# try to find a binding where all key elements are present
				if False in [ k in b for k in key ] :
					# this is not a binding for the key combination, move on...
					continue
				else :
					# yep, this one is good!
					return True
			return False
		else :
			if key not in self.variables : return False
			for b in self.bindings :
				if key in b : return True
			return False

	def __getitem__(self,key) :
		"""Emulation of the C{obj[key]} operator.  Slice notation is also available.
		The goal is to choose the right bindings among the available ones. The return values are always
		arrays  of bindings, ie, arrays of dictionaries mapping variable keys to L{Value} instances.
		The different value settings mean the followings:

		 - C{obj[key]} returns the bindings where C{key} has a valid value
		 - C{obj[key1,key2,...]} returns the bindings where I{all} C{key1,key2,...} have valid values
		 - C{obj[(key1,key2,...):(nkey1,nkey2,...)]} returns the bindings where all C{key1,key2,...} have
		 valid values and I{none} of the C{nkey1,nkey2,...} have valid values
		 - C{obj[:(nkey1,nkey2,...)]} returns the bindings where I{none} of the C{nkey1,nkey2,...} have valid values

		In all cases complete bindings are returned, ie, the values for other variables, not present among
		the keys in the call, may or may not be present depending on the query results.

		@param key: possible variable or array/tuple of keys with possible slice notation
		@return: list of bindings
		@rtype: array of variable -> L{Value}  dictionaries
		"""
		def _checkKeys(keys) :
			if len(keys) == 0 : return False
			for k in keys :
				if not isinstance(k,StringTypes) or not k in self.variables: return False
			return True

		def _nonSliceCase(key) :
			if isinstance(key,StringTypes) and key != "" and key in self.variables :
				# unicode or string:
				return [key]
			elif type(key) is ListType or type(key) is TupleType :
				if _checkKeys(key) :
					return key
			return False

		# The arguments should be reduced to arrays of variables, ie, unicode strings
		yes_keys = []
		no_keys  = []
		if type(key) is SliceType :
			# Note: None for start or stop is all right
			if key.start :
				yes_keys = _nonSliceCase(key.start)
				if not yes_keys: raise TypeError
			if key.stop :
				no_keys  = _nonSliceCase(key.stop)
				if not no_keys: raise TypeError
		else :
			yes_keys = _nonSliceCase(key)

		# got it right, now get the right binding line with the constraints
		retval = []
		for b in self.bindings :
			# first check whether the 'yes' part is all there:
			if False in [k in b for k in yes_keys] : continue
			if True  in [k in b for k in no_keys]  : continue
			# if we got that far, we shouild be all right!
			retval.append(b)
		# if retval is of zero length, no hit; an exception should be raised to stay within the python style
		if len(retval) == 0 :
			raise IndexError
		return retval

	def convert(self) :
		"""This is just a convenience method, returns C{self}.

		Although C{Binding} is not a subclass of L{QueryResult<SPARQLWrapper.Wrapper.QueryResult>}, it is returned as a result by
		L{SPARQLWrapper2.query}, just like L{QueryResult<SPARQLWrapper.Wrapper.QueryResult>} is returned by
		L{SPARQLWrapper.SPARQLWrapper.query}. Consequently,
		having an empty C{convert} method to imitate L{QueryResult's convert method<SPARQLWrapper.Wrapper.QueryResult.convert>} may avoid unnecessary problems.
		"""
		return self

##############################################################################################################

class SPARQLWrapper2(SPARQLWrapper.SPARQLWrapper) :
	"""Subclass of L{Wrapper<SPARQLWrapper.SPARQLWrapper>} that works with a JSON SELECT return result only. The query result 
    is automatically set to a L{Bindings} instance. Makes the average query processing a bit simpler..."""
	def __init__(self,baseURI,defaultGraph=None) :
		"""
		Class encapsulating a full SPARQL call. In contrast to the L{SPARQLWrapper<SPARQLWrapper.SPARQLWrapper>} superclass, the return format
		cannot be set (it is defaulted to L{JSON<Wrapper.JSON>}).
		@param baseURI: string of the SPARQL endpoint's URI
		@type baseURI: string
		@keyword defaultGraph: URI for the default graph. Default is None, can be set via an explicit call, too
		@type defaultGraph: string
		"""
		SPARQLWrapper.SPARQLWrapper.__init__(self,baseURI,returnFormat=JSON,defaultGraph=defaultGraph)

	def setReturnFormat(self,format) :
		"""Set the return format (overriding the L{inherited method<SPARQLWrapper.SPARQLWrapper.setReturnFormat>}).
		This method does nothing; this class instance should work with JSON only. The method is defined
		just to avoid possible errors by erronously setting the return format.
		When using this class, the user can safely ignore this call.
		@param format: return format
		"""
		pass

	def query(self) :
		"""
			Execute the query and do an automatic conversion.

			Exceptions can be raised if either the URI is wrong or the HTTP sends back an error.
			The usual urllib2 exceptions are raised, which cover possible SPARQL errors, too.

			If the query type is I{not} SELECT, the method falls back to the
			L{corresponding method in the superclass<SPARQLWrapper.query>}.

			@return: query result
			@rtype: L{Bindings} instance
		"""
		res = SPARQLWrapper.SPARQLWrapper.query(self)
		if self.queryType == SELECT :
			return Bindings(res)
		else :
			return res

	def queryAndConvert(self) :
		"""This is here to override the inherited method; it is equivalent to L{query}.

		If the query type is I{not} SELECT, the method falls back to the
		L{corresponding method in the superclass<SPARQLWrapper.queryAndConvert>}.

		@return: the converted query result.
		"""
		if self.queryType == SELECT :
			return self.query()
		else :
			return SPARQLWrapper.SPARQLWrapper.queryAndConvert(self)