1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
|
Utilities & convenience functions
=================================
For RDF programming, RDFLib and Python may be the fastest tools,
but we try hard to make them the easiest and most convenient to use and thus the *fastest* overall!
This is a collection of hints and pointers for hassle-free RDF coding.
Functional properties
---------------------
Use :meth:`~rdflib.graph.Graph.value` and
:meth:`~rdflib.graph.Graph.set` to work with :term:`functional
property` instances, i.e. properties than can only occur once for a resource.
.. code-block:: python
from rdflib import Graph, URIRef, Literal, BNode
from rdflib.namespace import FOAF, RDF
g = Graph()
g.bind("foaf", FOAF)
# Add demo data
bob = URIRef("http://example.org/people/Bob")
g.add((bob, RDF.type, FOAF.Person))
g.add((bob, FOAF.name, Literal("Bob")))
g.add((bob, FOAF.age, Literal(38)))
# To get a single value, use 'value'
print(g.value(bob, FOAF.age))
# prints: 38
# To change a single of value, use 'set'
g.set((bob, FOAF.age, Literal(39)))
print(g.value(bob, FOAF.age))
# prints: 39
Slicing graphs
--------------
Python allows slicing arrays with a ``slice`` object, a triple of
``start``, ``stop`` and ``step-size``:
.. code-block:: python
for i in range(20)[2:9:3]:
print(i)
# prints:
# 2, 5, 8
RDFLib graphs override ``__getitem__`` and we pervert the slice triple
to be a RDF triple instead. This lets slice syntax be a shortcut for
:meth:`~rdflib.graph.Graph.triples`,
:meth:`~rdflib.graph.Graph.subject_predicates`,
:meth:`~rdflib.graph.Graph.contains`, and other Graph query-methods:
.. code-block:: python
from rdflib import Graph, URIRef, Literal, BNode
from rdflib.namespace import FOAF, RDF
g = Graph()
g.bind("foaf", FOAF)
# Add demo data
bob = URIRef("http://example.org/people/Bob")
bill = URIRef("http://example.org/people/Bill")
g.add((bob, RDF.type, FOAF.Person))
g.add((bob, FOAF.name, Literal("Bob")))
g.add((bob, FOAF.age, Literal(38)))
g.add((bob, FOAF.knows, bill))
print(g[:])
# same as
print(iter(g))
print(g[bob])
# same as
print(g.predicate_objects(bob))
print(g[bob: FOAF.knows])
# same as
print(g.objects(bob, FOAF.knows))
print(g[bob: FOAF.knows: bill])
# same as
print((bob, FOAF.knows, bill) in g)
print(g[:FOAF.knows])
# same as
print(g.subject_objects(FOAF.knows))
See :mod:`examples.slice` for a complete example.
.. note:: Slicing is convenient for run-once scripts for playing around
in the Python ``REPL``, however since slicing returns
tuples of varying length depending on which parts of the
slice are bound, you should be careful using it in more
complicated programs. If you pass in variables, and they are
``None`` or ``False``, you may suddenly get a generator of
different length tuples back than you expect.
SPARQL Paths
------------
`SPARQL property paths
<http://www.w3.org/TR/sparql11-property-paths/>`_ are possible using
overridden operators on URIRefs. See :mod:`examples.foafpaths` and
:mod:`rdflib.paths`.
Serializing a single term to N3
-------------------------------
For simple output, or simple serialisation, you often want a nice
readable representation of a term. All terms (URIRef, Literal etc.) have a
``n3``, method, which will return a suitable N3 format:
.. code-block:: python
from rdflib import Graph, URIRef, Literal
from rdflib.namespace import FOAF
# A URIRef
person = URIRef("http://xmlns.com/foaf/0.1/Person")
print(person.n3())
# prints: <http://xmlns.com/foaf/0.1/Person>
# Simplifying the output with a namespace prefix:
g = Graph()
g.bind("foaf", FOAF)
print(person.n3(g.namespace_manager))
# prints foaf:Person
# A typed literal
l = Literal(2)
print(l.n3())
# prints "2"^^<http://www.w3.org/2001/XMLSchema#integer>
# Simplifying the output with a namespace prefix
# XSD is built in, so no need to bind() it!
l.n3(g.namespace_manager)
# prints: "2"^^xsd:integer
Parsing data from a string
--------------------------
You can parse data from a string with the ``data`` param:
.. code-block:: python
from rdflib import Graph
g = Graph().parse(data="<a:> <p:> <p:>.")
for r in g.triples((None, None, None)):
print(r)
# prints: (rdflib.term.URIRef('a:'), rdflib.term.URIRef('p:'), rdflib.term.URIRef('p:'))
Commandline-tools
-----------------
RDFLib includes a handful of commandline tools, see :mod:`rdflib.tools`.
|
