multiplicity.py

from enum import Enum
from math import inf


class Multiplicity(Enum):
    """
    Defines multiplicities.

    >>> Multiplicity.OPTIONAL.min
    0
    >>> Multiplicity.OPTIONAL.max
    1
    >>> Multiplicity.REQUIRED.min
    1
    >>> Multiplicity.REQUIRED.max
    1
    >>> Multiplicity.VARIADIC.min
    0
    >>> Multiplicity.VARIADIC.max
    inf
    >>> Multiplicity.POLYADIC.min
    1
    >>> Multiplicity.POLYADIC.max
    inf
    >>> Multiplicity.alias("?") == Multiplicity.OPTIONAL
    True
    >>> Multiplicity.alias("1") == Multiplicity.REQUIRED
    True
    >>> Multiplicity.alias("*") == Multiplicity.VARIADIC
    True
    >>> Multiplicity.alias("+") == Multiplicity.POLYADIC
    True
    >>> Multiplicity.alias("X")
    Traceback (most recent call last):
    ...
    AttributeError: No such alias defined for multiplicities: X
    """

    #: Indicates `0` or `1` multiplicity (`?`).
    OPTIONAL = (0, 1)

    #: Indicates `1` multiplicity (`1`).
    REQUIRED = (1, 1)

    #: Indicates `0 or more` multiplicity (`*`).
    VARIADIC = (0, inf)

    #: Indicates `1 or more` multiplicity (`+`) (Though the name implies 2 or more in maths literature).
    POLYADIC = (1, inf)

    #: Defines regular expression like aliases for multiplicities.
    __ALIASES__ = {
        "?": "OPTIONAL",
        "1": "REQUIRED",
        "*": "VARIADIC",
        "+": "POLYADIC"
    }

    @property
    def min(self):
        return self.value[0]

    @property
    def max(self):
        return self.value[1]

    @classmethod
    def alias(cls, symbol: str) -> "Multiplicity":
        """
        Returns the multiplicity for the given regular expression like alias.

        :param symbol: The regular expression like alias.
        :return: The multiplicity for the given alias.
        """
        ## If we don't have the symbol in the aliases, raise attribure error.
        if symbol not in cls.__ALIASES__:
            raise AttributeError("No such alias defined for multiplicities: {}".format(symbol))

        ## Return the multiplicity for the given symbol.
        return cls[cls.__ALIASES__[symbol]]