On Sep 29, 2015, at 09:58, Emile van Sebille <emile@fenx.com> wrote:
On 9/29/2015 9:20 AM, Rob Cliffe wrote: Why not
def __init__(self, vertices=None, edges=None, weights=None, source_nodes=None): self.vertices = vertices if vertices is not None else [] self.edges = edges if edges is not None else [] self.weights = weights if weights is not None else {} self.source_nodes = source_nodes if source_nodes is not None else []
I don't understand why not:
self.vertices = vertices or [] self.edges = edges or [] self.weights = weights or {} self.source_nodes = source_nodes or []
Because empty containers are just as falsey as None. So, if I pass in a shared list, your "vertices or []" will replace it with a new, unshared list; if I pass a tuple because I need an immutable graph, you'll replace it with a mutable list; if I pass in a blist.sortedlist, you'll replace it with a plain list. Worse, this will only happen if the argument I pass happens to be empty, which I may not have thought to test for. This is the same reason you don't use "if spam:" when you meant "if spam is not None:", which is explained in PEP 8. Also, I believe the PEP for ternary if-else explains why this is an "attractive nuisance" misuse of or, as one of the major arguments for why a ternary expression should be added.