posmatch 0.5.0

Positional sub-pattern matching for custom classes.

posmatch

Positional sub-pattern matching for custom classes.

Requirements

Python 3.9 or higher.

Note: Although this package can be installed and used in Python 3.9+, its usage only makes sense with the pattern matching feature introduced in Python 3.10. All code snippets below require Python 3.10+.

Installation

pip install posmatch

Usage

The pos_match decorator

from posmatch import pos_match

@pos_match
class Color:

    def __init__(self, r, g, b):
        self.r = r
        self.g = g
        self.b = b

color = Color(64, 64, 64)

match color:
    case Color(0, 0, _):
        print('Shade of blue')
    case Color(red, green, blue) if red == green == blue:
        print('Shade of grey')

Output:

Shade of grey

The PosMatchMeta metaclass

from posmatch import PosMatchMeta

class Date(metaclass=PosMatchMeta):

    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day = day

date = Date(2121, 1, 1)

match date:
    case Date(_, m, d) if m == 5 and d == 1:
        print('May Day')
    case Date(y) if y > 2100:
        print('Distant future')

Output:

Distant future

The PosMatchMixin mix-in class

from posmatch import PosMatchMixin

class Rectangle(PosMatchMixin):

    def __init__(self, width, height):
        self.width = width
        self.height = height

shape = Rectangle(16, 16)

match shape:
    case Rectangle(w, h) if w == h:
        print('Square')
    case Rectangle(x, y) if x > y:
        print('Landscape')

Output:

Square