frozen.py

"""
frozen (immutable) data structures to support MultiIndexing

These are used for:

- .names (FrozenList)

"""

from pandas.core.base import PandasObject

from pandas.io.formats.printing import pprint_thing


class FrozenList(PandasObject, list):
    """
    Container that doesn't allow setting item *but*
    because it's technically non-hashable, will be used
    for lookups, appropriately, etc.
    """

    # Side note: This has to be of type list. Otherwise,
    #            it messes up PyTables type checks.

    def union(self, other) -> "FrozenList":
        """
        Returns a FrozenList with other concatenated to the end of self.

        Parameters
        ----------
        other : array-like
            The array-like whose elements we are concatenating.

        Returns
        -------
        diff : FrozenList
            The collection difference between self and other.
        """
        if isinstance(other, tuple):
            other = list(other)
        return type(self)(super().__add__(other))

    def difference(self, other) -> "FrozenList":
        """
        Returns a FrozenList with elements from other removed from self.

        Parameters
        ----------
        other : array-like
            The array-like whose elements we are removing self.

        Returns
        -------
        diff : FrozenList
            The collection difference between self and other.
        """
        other = set(other)
        temp = [x for x in self if x not in other]
        return type(self)(temp)

    # TODO: Consider deprecating these in favor of `union` (xref gh-15506)
    __add__ = __iadd__ = union

    def __getitem__(self, n):
        if isinstance(n, slice):
            return self.__class__(super().__getitem__(n))
        return super().__getitem__(n)

    def __radd__(self, other):
        if isinstance(other, tuple):
            other = list(other)
        return self.__class__(other + list(self))

    def __eq__(self, other):
        if isinstance(other, (tuple, FrozenList)):
            other = list(other)
        return super().__eq__(other)

    __req__ = __eq__

    def __mul__(self, other):
        return self.__class__(super().__mul__(other))

    __imul__ = __mul__

    def __reduce__(self):
        return self.__class__, (list(self),)

    def __hash__(self):
        return hash(tuple(self))

    def _disabled(self, *args, **kwargs):
        """This method will not function because object is immutable."""
        raise TypeError(
            "'{cls}' does not support mutable operations.".format(
                cls=self.__class__.__name__
            )
        )

    def __str__(self) -> str:
        return pprint_thing(self, quote_strings=True, escape_chars=("\t", "\r", "\n"))

    def __repr__(self) -> str:
        return f"{self.__class__.__name__}({str(self)})"

    __setitem__ = __setslice__ = __delitem__ = __delslice__ = _disabled
    pop = append = extend = remove = sort = insert = _disabled