structured_data._match.patterns.basic_patterns

Complexity

Total Complexity

13

Size/Duplication

Total Lines	87
Duplicated Lines	0 %

Importance

Changes

0

7 Methods

Rating	Name	Duplication	Size	Complexity
A	AsPattern.__new__()	0	6	2
A	Pattern.name()	0	4	1
A	Pattern.__getitem__()	0	2	1
A	AsPattern.destructure()	0	21	3
A	AsPattern.pattern()	0	4	1
A	Pattern.__new__()	0	8	4
A	AsPattern.structure()	0	4	1

"""The simplest patterns."""

from __future__ import annotations

import keyword
import sys
import typing

from .compound_match import CompoundMatch

DISCARD = object()


class Pattern(tuple):
    """A matcher that binds a value to a name.

    A ``Pattern`` can be indexed with another matcher to produce an
    ``AsPattern``. When matched with a value, an ``AsPattern`` both binds the
    value to the name, and uses the matcher to match the value, thereby
    constraining it to have a particular shape, and possibly introducing
    further bindings.
    """

    __slots__ = ()

    def __new__(cls, name: str):
        if name == "_":
            return DISCARD
        if not name.isidentifier():
            raise ValueError
        if keyword.iskeyword(name):
            raise ValueError
        return super().__new__(cls, (sys.intern(name),))  # type: ignore

    @property
    def name(self) -> str:
        """Return the name of the matcher."""
        return tuple.__getitem__(self, 0)

    def __getitem__(self, other) -> AsPattern:
        return AsPattern(self, other)


class AsPattern(CompoundMatch, tuple):
    """A matcher that contains further bindings."""

    __slots__ = ()

    def __new__(  # type: ignore
        cls, pattern: Pattern, structure
    ) -> typing.Union[Pattern, AsPattern]:
        if structure is DISCARD:
            return pattern
        return super().__new__(cls, (pattern, structure))  # type: ignore

    @property
    def pattern(self) -> Pattern:
        """Return the left-hand-side of the as-match."""
        return self[0]

    @property
    def structure(self):
        """Return the right-hand-side of the as-match."""
        return self[1]

    def destructure(self, value):
        """Return a tuple of sub-values to check.

        By default, return the value twice.

        If ``isinstance(value, AsPattern)``, return two values:
        First, the structure to match against.
        Second, by default, the value itself, but if ``value is self``,
        instead return the pattern to bind to.

        The behavior of returning the full AsPattern when ``value is not self``
        is present because it makes it possible to sensically use an AsPattern
        as a target, which I don't know if there's a good reason for, but it
        was easy to implement.
        """
        if isinstance(value, AsPattern):
            # Letting mutmut touch this line thoroughly locked things up.
            if value is self:  # pragma: no mutate
                return (self.structure, self.pattern)
            return (value.structure, value)
        return (value, value)