Decimal adapter registration moved from C to Python

Fixes Decimal adaptation in sub-interpreter, where the Decimal class has
a different identity from the one in the main interpreter.

Closes ticket #52.

NEWS

@@ -6,6 +6,8 @@ What's new in psycopg 2.4.3
   - Added support for arrays of hstores and composite types (ticket #66).
   - Fixed segfault in case of transaction started with connection lost
     (and possibly other events).
+  - Fixed adaptation of Decimal type in sub-interpreters, such as in
+    certain mod_wsgi configurations (ticket #52).
   - Rollback connections in transaction or in error before putting them
     back into a pool. Also discard broken connections (ticket #62).
   - Lazy import of the slow uuid module, thanks to Marko Kreen.

lib/__init__.py

@@ -85,5 +85,17 @@ import psycopg2.extensions as _ext
 _ext.register_adapter(tuple, _ext.SQL_IN)
 _ext.register_adapter(type(None), _ext.NoneAdapter)
 
+# Register the Decimal adapter here instead of in the C layer.
+# This way a new class is registered for each sub-interpreter.
+# See ticket #52
+try:
+    from decimal import Decimal
+except ImportError:
+    pass
+else:
+    from psycopg2._psycopg import Decimal as Adapter
+    _ext.register_adapter(Decimal, Adapter)
+    del Decimal, Adapter
+
 __all__ = filter(lambda k: not k.startswith('_'), locals().keys())
 

psycopg/psycopgmodule.c

@@ -322,7 +322,6 @@ static void
 psyco_adapters_init(PyObject *mod)
 {
     PyObject *call;
-    PyTypeObject *type;
 
     microprotocols_add(&PyFloat_Type, NULL, (PyObject*)&pfloatType);
 #if PY_MAJOR_VERSION < 3
@@ -353,9 +352,6 @@ psyco_adapters_init(PyObject *mod)
 
     microprotocols_add(&PyList_Type, NULL, (PyObject*)&listType);
 
-    if ((type = (PyTypeObject*)psyco_GetDecimalType()) != NULL)
-        microprotocols_add(type, NULL, (PyObject*)&pdecimalType);
-
     /* the module has already been initialized, so we can obtain the callable
        objects directly from its dictionary :) */
     call = PyMapping_GetItemString(mod, "DateFromPy");