Confusion regarding constructor as default value

[aine_canby at yahoo.com]

Why are the following different?

def AddRow(self, rowName, tableRow=TableRow(ReleaseDate(""),
ExpiryDate(""))):
		# check to see if the row already exists, if not add it to the
container

		if not self.dict.has_key(rowName):
			self.dict[rowName] = tableRow

def AddRow(self, rowName, tableRow):
		# check to see if the row already exists, if not add it to the
container

		if not self.dict.has_key(rowName):
			self.dict[rowName] = TableRow(ReleaseDate(""), ExpiryDate(""))

It seems that when I use the first function that I'm getting duplicate
objects in self.dict

Thanks for your help,

Aine.