PL/Python: Avoid lossiness in float conversion

PL/Python uses str() to convert Python values back to PostgreSQL, but
str() is lossy for float values, so use repr() instead in that case.

Author: Marko Kreen <markokr@gmail.com>

src/pl/plpython/expected/plpython_types.out

@@ -354,6 +354,14 @@ CONTEXT:  PL/Python function "test_type_conversion_float8"
                             
 (1 row)
 
+SELECT * FROM test_type_conversion_float8(100100100.654321);
+INFO:  (100100100.654321, <type 'float'>)
+CONTEXT:  PL/Python function "test_type_conversion_float8"
+ test_type_conversion_float8 
+-----------------------------
+            100100100.654321
+(1 row)
+
 CREATE FUNCTION test_type_conversion_oid(x oid) RETURNS oid AS $$
 plpy.info(x, type(x))
 return x

src/pl/plpython/plpy_typeio.c

@@ -760,6 +760,18 @@ PLyObject_ToDatum(PLyObToDatum *arg, int32 typmod, PyObject *plrv)
 
 	if (PyUnicode_Check(plrv))
 		plrv_bo = PLyUnicode_Bytes(plrv);
+	else if (PyFloat_Check(plrv))
+	{
+		/* use repr() for floats, str() is lossy */
+#if PY_MAJOR_VERSION >= 3
+		PyObject   *s = PyObject_Repr(plrv);
+
+		plrv_bo = PLyUnicode_Bytes(s);
+		Py_XDECREF(s);
+#else
+		plrv_bo = PyObject_Repr(plrv);
+#endif
+	}
 	else
 	{
 #if PY_MAJOR_VERSION >= 3

src/pl/plpython/sql/plpython_types.sql

@@ -122,6 +122,7 @@ SELECT * FROM test_type_conversion_float8(100);
 SELECT * FROM test_type_conversion_float8(-100);
 SELECT * FROM test_type_conversion_float8(5000000000.5);
 SELECT * FROM test_type_conversion_float8(null);
+SELECT * FROM test_type_conversion_float8(100100100.654321);
 
 
 CREATE FUNCTION test_type_conversion_oid(x oid) RETURNS oid AS $$