# -*- coding: utf-8 -*- """ @see: U{SPARQL Specification} @authors: U{Ivan Herman}, U{Sergio Fernández}, U{Carlos Tejo Alonso} @organization: U{World Wide Web Consortium} and U{Foundation CTIC}. @license: U{W3C® SOFTWARE NOTICE AND LICENSE} @requires: U{RDFLib} package. """ import SPARQLWrapper from SPARQLWrapper.Wrapper import JSON, SELECT import urllib2 from types import * ###################################################################################### class Value(object): """ 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(object): """ 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} 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 list or type(key) is tuple: # 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, basestring) or not k in self.variables: return False return True def _nonSliceCase(key) : if isinstance(key, basestring) and key != "" and key in self.variables : # unicode or string: return [key] elif type(key) is list or type(key) is tuple: 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 slice : # 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}, it is returned as a result by L{SPARQLWrapper2.query}, just like L{QueryResult} is returned by L{SPARQLWrapper.SPARQLWrapper.query}. Consequently, having an empty C{convert} method to imitate L{QueryResult's convert method} may avoid unnecessary problems. """ return self ############################################################################################################## class SPARQLWrapper2(SPARQLWrapper.SPARQLWrapper): """Subclass of L{Wrapper} 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} superclass, the return format cannot be set (it is defaulted to L{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 """ super(SPARQLWrapper2, self).__init__(baseURI, returnFormat=JSON, defaultGraph=defaultGraph) def setReturnFormat(self, format): """Set the return format (overriding the L{inherited method}). 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}. @return: query result @rtype: L{Bindings} instance """ res = super(SPARQLWrapper2, self).query() 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}. @return: the converted query result. """ if self.queryType == SELECT: return self.query() else: return super(SPARQLWrapper2, self).queryAndConvert()