On Nov 1, 4:55 pm, stef mientki <[EMAIL PROTECTED]> wrote: > Chris Mellon wrote: > > On Nov 1, 2007 3:18 PM, stef mientki <[EMAIL PROTECTED]> wrote: > > >> hello, > > >> I would like to use instance parameters as a default value, like this: > > >> class PlotCanvas(wx.Window): > >> def __init__(self) > >> self.Buf_rp = 0 > >> self.Buf_wp = 0 > > >> def Draw ( self, x1 = self.Buf_rp, x2 = self.Buf_wp ) : > > >> is something like this possible ? > > > No, because self is not in scope at the time that default arguments > > are evaluated. The traditional workaround is to use x1=None, and if x1 > > is None: x1 = self.Buf_rp. > > thanks Chris, > I was afraid of that ;-) > > cheers, > Stef
That's the standard approach but if you use it a lot, the recipe at http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/502206 for arbitrary default expressions evaluated at call time (rather than definition time) may come in handy: class PlotCanvas(wx.Window): def __init__(self): self.Buf_rp = 0 self.Buf_wp = 0 @revaluatable def Draw(self, x1 = Deferred('self.Buf_rp'), x2 = Deferred('self.Buf_wp')): return (x1,x2) p = PlotCanvas() p.Buf_rp = 2 p.Buf_wp = -1 print p.Draw(), p.Draw(x2='foo') HTH, George -- http://mail.python.org/mailman/listinfo/python-list
