</Sarcasm>
But seriously, I think there's no one way to do things anymore especially if it holds up productivity and effectiveness. Let the pattern matching begin.
[foo(y, y) for x in xs for y in [f(x)]]
Is this Pythonic? Perhaps not, but mainly because multiline list comprehensions are frowned on in general. I think people tend to get too dogmatic about that.Python does that with tuples:
a, b = b, a
But it just stops there. To be fair, I don't know how much power it would gain by going further either. Never made that question.Pattern matching is normally (in functional languages like Scala and Haskell anyway) defined as a way of taking a union type and handling each one safely. It's a sort of functional alternative to polymorphism.
That is, polymorphic code
class Dog(Animal):
def make_noise(self):
return "bork bork"
class Duck(Animal):
def make_noise(self):
return "quack"
would, with pattern matching be (in pseudo haskell I hope) make_noise :: Animal -> str
make_noise Duck = "quack"
make_noise Dog = "bork bork"
In other words, in an oop style you delegate to the object that it implements all methods. Whereas with pattern matching you can have a type delegate to each of the functions that can operate on it to handle it correctly. (This explanation is a disservice to functional styles, its a lot more elegant than what I describe if you do it correctly).So a maybe type (equivalent to an Optional) is simply a sum over just and nothing (the two components). If you fall to handle nothing, the program won't compile.
Animal would work the same way. Add "Cow" as an animal, and your program won't compile until everything sanely handles Cow.
So more like a switch case over a set of options where the compiler prevents you from forgetting any.
With PEP 572 it wasn't like that. There wasn't a Pythonic way to do list comprehensions which used the same expensive to evaluate expression two times in it and it was I think the only glaring syntax weakness in comparison to languages which have a way to do that (like WHERE keyword in Haskell).