What colon (:) in Python mean in this case?

[deanhystad]

I guess it can be type notation for a class variable. Syntactically that is correct. Logically it doesn't make any sense.

So we have our class Point, a singleton that requires we make instances so they can be passed to where_is() to demonstrate how match works.

class Point():
    x: int
    y: int

def where_is(point):
    match point:
        case Point(x=0, y=0):
            print("Origin")
        case Point(x=0, y=y):
            print(f"Y={y}")
        case Point(x=x, y=0):
            print(f"X={x}")
        case Point():
            print("Somewhere else")
        case _:
            print("Not a point")

point = Point()
where_is(point)
Point.x, Point.y = 0, 0
where_is(point)
Point.x, Point.y = 0, 1
where_is(point)
Point.x, Point.y = 1, 0
where_is(point)
where_is((0, 0))

That is just ugly. If the ": int" really is type annotation for class variables, this is a bad example.

It works better, but is longer, if x and y are properties.

class Point():
    def __init__(self, x=None, y=None):
        self._x, self._y = x, y

    @property
    def x(self) -> int:
        return self._x

    @x.setter
    def x(self, value: int):
        self._x = value

    @property
    def y(self) -> int:
        return self._y

    @y.setter
    def y(self, value: int) :
        self._y = value

 
def where_is(point):
    match point:
        case Point(x=0, y=0):
            print("Origin")
        case Point(x=0, y=y):
            print(f"Y={y}")
        case Point(x=x, y=0):
            print(f"X={x}")
        case Point():
            print("Somewhere else")
        case _:
            print("Not a point")
 
where_is(Point(0, 0))
where_is(Point(0, 1))
where_is(Point(1, 0))
where_is(Point())
where_is((0, 0))