Don't import psycopg2.tz into the C extension

This makes possible to import _psycopg directly, after adding the
package directory to the pythonpath. This enables hacks such as:

    sys.path.insert(0, '/path/to/psycopg2')
    import _psycopg
    sys.modules['psycopg2._psycopg'] = _psycopg
    sys.path.pop(0)

which can work around e.g. the problem of #201, freeze that cannot
freeze psycopg2. Well, freeze cannot freeze it because it's just not
designed to deal with C extensions. At least now the frozen application
can hack the pythonpath and work around the limitation by importing
_psycopg as above and then doing the rest of the imports normally.

Keeping long-lived references to python objects is bad anyway: the
tz module couldn't be reloaded before.

psycopg/adapter_datetime.c

@@ -35,9 +35,6 @@
 #include <string.h>
 
 
-extern HIDDEN PyObject *pyPsycopgTzModule;
-extern HIDDEN PyObject *pyPsycopgTzLOCAL;
-
 int
 psyco_adapter_datetime_init(void)
 {
@@ -430,6 +427,8 @@ psyco_TimeFromTicks(PyObject *self, PyObject *args)
 PyObject *
 psyco_TimestampFromTicks(PyObject *self, PyObject *args)
 {
+    PyObject *m = NULL;
+    PyObject *tz = NULL;
     PyObject *res = NULL;
     struct tm tm;
     time_t t;
@@ -438,18 +437,25 @@ psyco_TimestampFromTicks(PyObject *self, PyObject *args)
     if (!PyArg_ParseTuple(args, "d", &ticks))
         return NULL;
 
+    /* get psycopg2.tz.LOCAL from pythonland */
+    if (!(m = PyImport_ImportModule("psycopg2.tz"))) { goto exit; }
+    if (!(tz = PyObject_GetAttrString(m, "LOCAL"))) { goto exit; }
+
     t = (time_t)floor(ticks);
     ticks -= (double)t;
-    if (localtime_r(&t, &tm)) {
+    if (!localtime_r(&t, &tm)) {
+        PyErr_SetString(InterfaceError, "failed localtime call");
+        goto exit;
+    }
+
     res = _psyco_Timestamp(
         tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
         tm.tm_hour, tm.tm_min, (double)tm.tm_sec + ticks,
-            pyPsycopgTzLOCAL);
-    }
-	else {
-		PyErr_SetString(InterfaceError, "failed localtime call");
-	}
+        tz);
 
+exit:
+    Py_DECREF(tz);
+    Py_XDECREF(m);
     return res;
 }
 

psycopg/cursor_type.c

@@ -39,9 +39,6 @@
 #include <stdlib.h>
 
 
-extern PyObject *pyPsycopgTzFixedOffsetTimezone;
-
-
 /** DBAPI methods **/
 
 /* close method - close the cursor */
@@ -1842,8 +1839,17 @@ cursor_setup(cursorObject *self, connectionObject *conn, const char *name)
     self->tuple_factory = Py_None;
 
     /* default tzinfo factory */
-    Py_INCREF(pyPsycopgTzFixedOffsetTimezone);
-    self->tzinfo_factory = pyPsycopgTzFixedOffsetTimezone;
+    {
+        PyObject *m = NULL;
+        if ((m = PyImport_ImportModule("psycopg2.tz"))) {
+            self->tzinfo_factory = PyObject_GetAttrString(
+                    m, "FixedOffsetTimezone");
+            Py_DECREF(m);
+        }
+        if (!self->tzinfo_factory) {
+            return -1;
+        }
+    }
 
     Dprintf("cursor_setup: good cursor object at %p, refcnt = "
         FORMAT_CODE_PY_SSIZE_T,

psycopg/psycopgmodule.c

@@ -58,11 +58,6 @@
 #include "psycopg/adapter_datetime.h"
 HIDDEN PyObject *pyDateTimeModuleP = NULL;
 
-/* pointers to the psycopg.tz classes */
-HIDDEN PyObject *pyPsycopgTzModule = NULL;
-HIDDEN PyObject *pyPsycopgTzLOCAL = NULL;
-HIDDEN PyObject *pyPsycopgTzFixedOffsetTimezone = NULL;
-
 HIDDEN PyObject *psycoEncodings = NULL;
 
 #ifdef PSYCOPG_DEBUG
@@ -859,18 +854,6 @@ INIT_MODULE(_psycopg)(void)
     Py_TYPE(&pydatetimeType) = &PyType_Type;
     if (PyType_Ready(&pydatetimeType) == -1) goto exit;
 
-    /* import psycopg2.tz anyway (TODO: replace with C-level module?) */
-    pyPsycopgTzModule = PyImport_ImportModule("psycopg2.tz");
-    if (pyPsycopgTzModule == NULL) {
-        Dprintf("initpsycopg: can't import psycopg2.tz module");
-        PyErr_SetString(PyExc_ImportError, "can't import psycopg2.tz module");
-        goto exit;
-    }
-    pyPsycopgTzLOCAL =
-        PyObject_GetAttrString(pyPsycopgTzModule, "LOCAL");
-    pyPsycopgTzFixedOffsetTimezone =
-        PyObject_GetAttrString(pyPsycopgTzModule, "FixedOffsetTimezone");
-
     /* initialize the module and grab module's dictionary */
 #if PY_MAJOR_VERSION < 3
     module = Py_InitModule("_psycopg", psycopgMethods);