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.. _intro_to_parsing:
======================
Loading and saving RDF
======================
Reading an NT file
-------------------
RDF data has various syntaxes (``xml``, ``n3``, ``ntriples``, ``trix``, etc) that you might want to read. The simplest format is ``ntriples``, a line-based format. Create the file :file:`demo.nt` in the current directory with these two lines:
.. code-block:: n3
<http://bigasterisk.com/foaf.rdf#drewp> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/Person> .
<http://bigasterisk.com/foaf.rdf#drewp> <http://example.com/says> "Hello world" .
You need to tell RDFLib what format to parse, use the ``format`` keyword-parameter to :meth:`~rdflib.graph.Graph.parse`, you can pass either a mime-type or the name (a :doc:`list of available parsers <plugin_parsers>` is available).
If you are not sure what format your file will be, you can use :func:`rdflib.util.guess_format` which will guess based on the file extension.
In an interactive python interpreter, try this:
.. code-block:: pycon
>>> from rdflib import Graph
>>> g = Graph()
>>> g.parse("demo.nt", format="nt")
<Graph identifier=HCbubHJy0 (<class 'rdflib.graph.Graph'>)>
>>> len(g)
2
>>> import pprint
>>> for stmt in g:
... pprint.pprint(stmt)
...
(rdflib.term.URIRef('http://bigasterisk.com/foaf.rdf#drewp'),
rdflib.term.URIRef('http://example.com/says'),
rdflib.term.Literal(u'Hello world'))
(rdflib.term.URIRef('http://bigasterisk.com/foaf.rdf#drewp'),
rdflib.term.URIRef('http://www.w3.org/1999/02/22-rdf-syntax-ns#type'),
rdflib.term.URIRef('http://xmlns.com/foaf/0.1/Person'))
The final lines show how RDFLib represents the two statements in the file. The statements themselves are just length-3 tuples; and the subjects, predicates, and objects are all rdflib types.
Reading remote graphs
---------------------
Reading graphs from the net is just as easy:
.. code-block:: pycon
>>> g.parse("http://bigasterisk.com/foaf.rdf")
>>> len(g)
42
The format defaults to ``xml``, which is the common format for .rdf files you'll find on the net.
RDFLib will also happily read RDF from any file-like object, i.e. anything with a ``.read`` method.
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