match statement in python

Topics

• idiomatic python

Destructuring is the core strength of match. It allows you to unpack the contents of an object (like a tuple, list, or dataclass) directly within the case statement:

point = (0, 1)
match point:
    case (0, 0):
        print("Origin")
    case (0, y):
        # this is executed
        print(f"Y={y}")
    case (x, 0):
        print(f"X={x}")
    case (x, y):
        print(f"X={x}, Y={y}")
    case _:
        print("Not a point")
 
# Output: Y=1

In this example, the match statement attempts to match the point tuple against different patterns. The case (0, y) pattern destructures the tuple, assigning the second element to the variable y if the first element is 0.

@dataclass
class Point:
    x: int
    y: int
 
point = Point(1, 2)
 
match point:
    case Point(x=0, y=0):
        print("Origin")
    case Point(x=x_coord, y=y_coord):
        print(f"{x_coord=}, {y_coord=}")
 
# Output: x_coord=1, y_coord=2

This example destructures a dataclass. You can match against specific attribute values (e.g., x=0, y=0) or extract attribute values into variables (e.g., x_coord, y_coord).

Tip

It is recommended to consider match for destructuring in flow control, but avoid it when simple if statements are sufficient.

Use cases:

• when we need to simultaneously check the structure and extract parts of the data
• e.g: processing messages from external sources (like JSON), interpreting command structures, or handling different types of events etc

command = "pick up this box"
command_parts = command.split()
 
match command_parts:
    case ["north"] | ["go", "north"]:
        print("Moving north")
    case ["pick", "up", *args, obj] | ["pick", *args, obj, "up"]:
        print(f"Attempting to pick up {obj}")
    case _:
        print("Unrecognized action.")
 
# Output: Attempting to pick up box

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