sql_db: Avoid using inspect.stack(), use failsafe alternative.

Inspecting the full stack just to learn the file:line info for debugging
purposes is both expensive and error-prone. Write an alternative function
in tools/func.py that will just go N frames back and try to get the info.

bzr revid: p_christ@hol.gr-20101123135742-2jp75f3uxyg3a6b6

bin/sql_db.py

@@ -51,11 +51,11 @@ psycopg2.extensions.register_type(psycopg2.extensions.new_type((700, 701, 1700,)
 
 
 import tools
-from tools.func import wraps
+from tools.func import wraps, frame_codeinfo
 from datetime import datetime as mdt
 from datetime import timedelta
 import threading
-from inspect import stack
+from inspect import currentframe
 
 import re
 re_from = re.compile('.* from "?([a-zA-Z_0-9]+)"? .*$');
@@ -93,7 +93,7 @@ class Cursor(object):
         self._obj = self._cnx.cursor(cursor_factory=psycopg1cursor)
         self.__closed = False   # real initialisation value
         self.autocommit(False)
-        self.__caller = tuple(stack()[2][1:3])
+        self.__caller = frame_codeinfo(currentframe(),2)
 
     def __del__(self):
         if not self.__closed:

bin/tools/func.py

@@ -93,3 +93,24 @@ def synchronized(lock_attr='_lock'):
     return decorator
 
 
+
+from inspect import getsourcefile
+
+def frame_codeinfo(fframe, back=0):
+    """ Return a (filename, line) pair for a previous frame .
+        @return (filename, lineno) where lineno is either int or string==''
+    """
+    
+    try:
+        if not fframe:
+            return ("<unknown>", '')
+        for i in range(back):
+            fframe = fframe.f_back
+        try:
+            fname = getsourcefile(fframe)
+        except TypeError:
+            fname = '<builtin>'
+        lineno = fframe.f_lineno or ''
+        return (fname, lineno)
+    except Exception:
+        return ("<unknown>", '')