On Sun, Jul 15, 2012 at 9:51 PM, Chris Angelico <ros...@gmail.com> wrote: >> if bool(obj) and a==b: # Correct! >> if obj and a==b: # Incorrect! > > That still doesn't answer the question of what bool(obj) should do if > obj is not a bool, and why if can't do the exact same thing, since if, > by definition, is looking for a boolean state selector.
If can obviously do the exact same thing -- it does, in Python. I don't agree with the angle that Rick is spinning, so let me write my own: By forcing the objects in conditional to be booleans, you are forced to do something to non-booleans to convert them. By doing so, you will help inform the reader what the non-boolean is, which makes it easier for them to figure out the code. For example, instead of "if stack:" or "if bool(stack):", we could use "if stack.isempty():". This line tells us explicitly that stack is a container. Or instead of "if dist:" or "if bool(dist):" we could use "if dist == 0:". This tells us explicitly that stack is a number. Supposedly this makes it easier to read code. It certainly reads more like English! :) As far as I know, the only use of having a polymorphic boolean conversion is reducing the amount of typing we do. Generally objects with otherwise different interfaces are not interchangeable just because they can be converted to booleans, so you wouldn't lose much by being forced to explicitly convert to boolean with something interface-specific. -- Devin -- http://mail.python.org/mailman/listinfo/python-list