Initialize UTC in the timezones cache

Not having it might cause spurious errors in particular cases, we see it
failing sometimes in the CI on Windows (which lacks the timezone
database) on Python 3.6 with a ridiculous:

    unknown PostgreSQL timezone: 'UTC'; will use UTC

The similar cache on the Python side is primed the same way.

diff --git a/psycopg_c/psycopg_c/types/datetime.pyx b/psycopg_c/psycopg_c/types/datetime.pyx
index 4f7d2257646e2d428c849157e0dcaf72a2f636bc..448ddd173b73d018cf83ec8607184f3f2b72cbb5 100644 (file)
--- a/psycopg_c/psycopg_c/types/datetime.pyx
+++ b/psycopg_c/psycopg_c/types/datetime.pyx
@@ -1105,13 +1105,17 @@ cdef object _timezone_from_seconds(int sec, __cache={}):
     return tz
 
 
-cdef object _timezone_from_connection(pq.PGconn pgconn, __cache={}):
+cdef _timezones = {}
+_timezones[None] = timezone_utc
+_timezones[b"UTC"] = timezone_utc
+
+cdef object _timezone_from_connection(pq.PGconn pgconn):
     """Return the Python timezone info of the connection's timezone."""
     if pgconn is None:
         return timezone_utc
 
-    tzname = libpq.PQparameterStatus(pgconn._pgconn_ptr, b"TimeZone")
-    cdef PyObject *ptr = PyDict_GetItem(__cache, tzname)
+    cdef bytes tzname = libpq.PQparameterStatus(pgconn._pgconn_ptr, b"TimeZone")
+    cdef PyObject *ptr = PyDict_GetItem(_timezones, tzname)
     if ptr != NULL:
         return <object>ptr
 
@@ -1130,7 +1134,7 @@ cdef object _timezone_from_connection(pq.PGconn pgconn, __cache={}):
         )
         zi = timezone_utc
 
-    __cache[tzname] = zi
+    _timezones[tzname] = zi
     return zi