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Python:Match

"Structural Pattern Matching" 은 파이썬 3.10 부터 도입된 문법이다. match ~ case 문 이다.

Introduced in Python 3.10, Structural Pattern Matching gives Python developers a powerful alternative to traditional conditional logic.

  • Unpacking
  • Starred unpacking
  • Partial assignment
  • Class & Class attribute matching
  • Complex pattern with wildcard
  • Guard

Examples

At its most basic, the syntax looks like this: 

match value:
    case pattern1:
        # code if value matches pattern1
    case pattern2:
        # code if value matches pattern2
    case _:
        # wildcard case (default)

The real power comes with destructuring! Match patterns break down complex data structures and extract values in a single step. 

# Destructuring and matching tuples
match point:
    case (0, 0):
        return "Origin"
    case (0, y):
        return f"Y-axis at {y}"
    case (x, 0):
        return f"X-axis at {x}"
    case (x, y):
        return f"Point at ({x}, {y})"

# Using OR pattern (|) to match multiple patterns
match day:
    case ("Monday"
          | "Tuesday"
          | "Wednesday"
          | "Thursday"
          | "Friday"):
        return "Weekday"
    case "Saturday" | "Sunday":
        return "Weekend"

# Guard clauses with inline 'if' statements
match temperature:
    case temp if temp < 0:
        return "Freezing"
    case temp if temp < 20:
        return "Cold"
    case temp if temp < 30:
        return "Warm"
    case _:
        return "Hot"



# Capture entire collections using asterisk (*)
match numbers:
    case [f]:
        return f"First: {f}"
    case [f, l]:
        return f"First: {f}, Last: {l}"
    case [f, *m, l]:
        return f"First: {f}, Middle: {m}, Last: {l}"
    case []:
        return "Empty list"

You can also combine match-case with other Python features like walrus operators to create even more powerful patterns. 

# Check if a packet is valid or not
packet: list[int] = [0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07]

match packet:
    case [c1, c2, *data, footer] if (  # Deconstruct packet into header, data, and footer
        (checksum := c1 + c2) == sum(data) and  # Check that the checksum is correct
        len(data) == footer  # Check that the data length is correct
    ):
        print(f"Packet received: {data} (Checksum: {checksum})")
    case [c1, c2, *data]:  # Failure case where structure is correct but checksum is wrong
        print(f"Packet received: {data} (Checksum Failed)")
    case [_, *__]:  # Failure case where packet is too short
        print("Invalid packet length")
    case []:  # Failure case where packet is empty
        print("Empty packet")
    case _:  # Failure case where packet is invalid
        print("Invalid packet")

See also

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