Raise error when dump is called with non-finite floats

pytoml/writer.py

 from __future__ import unicode_literals
-import io, datetime, sys
+import io, datetime, math, sys
 
 if sys.version_info[0] == 3:
     long = int
@@ -61,7 +61,10 @@ def _format_value(v):
     if isinstance(v, int) or isinstance(v, long):
         return unicode(v)
     if isinstance(v, float):
-        return repr(v)
+        if math.isnan(v) or math.isinf(v):
+            raise ValueError("{0} is not a valid TOML value".format(v))
+        else:
+            return repr(v)
     elif isinstance(v, unicode) or isinstance(v, bytes):
         return _escape_string(v)
     elif isinstance(v, datetime.datetime):

test/test_writer.py

+from __future__ import unicode_literals
+
+import pytest
+
+import pytoml as toml
+
+
+@pytest.mark.parametrize("value", [
+    float("NaN"),
+    float("Inf"),
+    -float("Inf"),
+])
+def test_attempting_to_write_non_number_floats_raises_error(value):
+    error = pytest.raises(ValueError, lambda: toml.dumps({"value": value}))
+    assert str(error.value) == "{0} is not a valid TOML value".format(value)