No subject

Thu Mar 8 10:26:06 GMT 2007

1.	algorithms and design
2.	attribute lookups
3.	function calls
4.	python-c boundary crosses

There's nothing you can do about the first one in this case, but you can try 
to minimize the others.

In the case of  "self.key( col, ascending ).toInt( )" it's two attribute 
lookups, two function calls, and one extension call.  Disassembling this 
confirms it:

[1] >>> def compare(self, item, column, ascending):
   ...:     x = self.key(column, ascending).toInt()

[2] >>> import dis
[3] >>> dis.dis(compare)
  2           0 LOAD_FAST                0 (self)
              3 LOAD_ATTR                1 (key)
              6 LOAD_FAST                2 (column)
              9 LOAD_FAST                3 (ascending)
             12 CALL_FUNCTION            2
             15 LOAD_ATTR                4 (toInt)
             18 CALL_FUNCTION            0
             21 STORE_FAST               4 (x)
             24 LOAD_CONST               0 (None)
             27 RETURN_VALUE

(the boundary cross isn't there, of course)

>     # C++ Prototype
>     # int MyListViewItem::compare( QListViewItem *i, int col,
>     #                             bool ascending ) const
>     def compare( self, i, col, ascending ):
>         x = self.key( col, ascending ).toInt( );
>         y = i.key( col, ascending).toInt( );
>         return x[0]-y[0];

Now, you've already implemented 'compare()' in python, so one thing  you want 
to avoid is crossing the extension boundary again, as pyqt has already called 
into your python code.  Instead of calling key() twice,  then toInt() twice, 
you could do:

    def compare(self, item, column, ascending):
            a = int(str(self.text(column))) 
        except (ValueError, ):
            a = self.text(column)
            b = int(str(item.text(column)))
            b = item.text(column)
        return cmp(a, b)

I've tested this on a list view of mine, and it works with small data sets.  
Could you try it and see if it's better or worse with your data?  You might 
try timing the header click slot.

Troy Melhase, troy at
I have sworn upon the altar of God eternal hostility against every form of 
tyranny over the mind of man. - Thomas Jefferson

More information about the PyQt mailing list