Merge pull request #658 from joernhees/turtle_infty_nan

improve serialization of inf/nan, closes #655 

2 files changed, 102 insertions, 0 deletions

diff --git a/rdflib/term.py b/rdflib/term.py
index e2dd387d..37c0e84a 100644
--- a/rdflib/term.py
+++ b/rdflib/term.py
@@ -38,6 +38,7 @@ __all__ = [
 import logging
 logger = logging.getLogger(__name__)
 import warnings
+import math
 
 import base64
 import xml.dom.minidom
@@ -1195,6 +1196,15 @@ class Literal(Identifier):
         '''
         if use_plain and self.datatype in _PLAIN_LITERAL_TYPES:
             if self.value is not None:
+                # If self is inf or NaN, we need a datatype
+                # (there is no plain representation)
+                if self.datatype in _NUMERIC_INF_NAN_LITERAL_TYPES:
+                    try:
+                        v = float(self)
+                        if math.isinf(v) or math.isnan(v):
+                            return self._literal_n3(False, qname_callback)
+                    except ValueError:
+                        return self._literal_n3(False, qname_callback)
 
                 # this is a bit of a mess -
                 # in py >=2.6 the string.format function makes this easier
@@ -1221,6 +1231,20 @@ class Literal(Identifier):
                 quoted_dt = qname_callback(datatype)
             if not quoted_dt:
                 quoted_dt = "<%s>" % datatype
+            if datatype in _NUMERIC_INF_NAN_LITERAL_TYPES:
+                try:
+                    v = float(self)
+                    if math.isinf(v):
+                        # py string reps: float: 'inf', Decimal: 'Infinity"
+                        # both need to become "INF" in xsd datatypes
+                        encoded = encoded.replace('inf', 'INF').replace(
+                            'Infinity', 'INF')
+                    if math.isnan(v):
+                        encoded = encoded.replace('nan', 'NaN')
+                except ValueError:
+                    # if we can't cast to float something is wrong, but we can
+                    # still serialize. Warn user about it
+                    warnings.warn("Serializing weird numerical %r" % self)
 
         language = self.language
         if language:
@@ -1388,6 +1412,13 @@ _PLAIN_LITERAL_TYPES = (
     _XSD_DECIMAL,
 )
 
+# these have special INF and NaN XSD representations
+_NUMERIC_INF_NAN_LITERAL_TYPES = (
+    URIRef(_XSD_PFX + 'float'),
+    _XSD_DOUBLE,
+    _XSD_DECIMAL,
+)
+
 
 def _castPythonToLiteral(obj):
     """
diff --git a/test/test_issue655.py b/test/test_issue655.py
new file mode 100644
index 00000000..1c640709
--- /dev/null
+++ b/test/test_issue655.py
@@ -0,0 +1,71 @@
+from decimal import Decimal
+import unittest
+from rdflib import Graph, Namespace, URIRef, Literal, XSD
+from rdflib.compare import to_isomorphic
+
+
+class TestIssue655(unittest.TestCase):
+
+    def test_issue655(self):
+        # make sure that inf and nan are serialized correctly
+        dt = XSD['double'].n3()
+        self.assertEqual(
+            Literal(float("inf"))._literal_n3(True),
+            '"INF"^^%s' % dt
+        )
+        self.assertEqual(
+            Literal(float("-inf"))._literal_n3(True),
+            '"-INF"^^%s' % dt
+        )
+        self.assertEqual(
+            Literal(float("nan"))._literal_n3(True),
+            '"NaN"^^%s' % dt
+        )
+
+        dt = XSD['decimal'].n3()
+        self.assertEqual(
+            Literal(Decimal("inf"))._literal_n3(True),
+            '"INF"^^%s' % dt
+        )
+        self.assertEqual(
+            Literal(Decimal("-inf"))._literal_n3(True),
+            '"-INF"^^%s' % dt
+        )
+        self.assertEqual(
+            Literal(Decimal("nan"))._literal_n3(True),
+            '"NaN"^^%s' % dt
+        )
+
+        self.assertEqual(
+            Literal("inf", datatype=XSD['decimal'])._literal_n3(True),
+            '"INF"^^%s' % dt
+        )
+
+        # assert that non-numerical aren't changed
+        self.assertEqual(
+            Literal('inf')._literal_n3(True),
+            '"inf"'
+        )
+        self.assertEqual(
+            Literal('nan')._literal_n3(True),
+            '"nan"'
+        )
+
+        PROV = Namespace('http://www.w3.org/ns/prov#')
+
+        bob = URIRef("http://example.org/object/Bob")
+
+        # g1 is a simple graph with an infinite and a nan values
+        g1 = Graph()
+        g1.add((bob, PROV.value, Literal(float("inf"))))
+        g1.add((bob, PROV.value, Literal(float("nan"))))
+
+        # Build g2 out of the deserialisation of g1 serialisation
+        g2 = Graph()
+        g2.parse(data=g1.serialize(format='turtle'), format='turtle')
+
+        self.assertTrue(to_isomorphic(g1) == to_isomorphic(g2))
+
+
+if __name__ == "__main__":
+    unittest.main()