You can use a sentinel if you want to allow None as an argument. More on that, along with a way to use mutable defaults productively: http://effbot.org/zone/de

You can use a sentinel if you want to allow None as an argument. More on that, along with a way to use mutable defaults productively: http://effbot.org/zone/default-values.htm http://effbot.org/zone/default-values.htm