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"""The simplest patterns.""" |
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from __future__ import annotations |
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import keyword |
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import sys |
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import typing |
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9
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from .compound_match import CompoundMatch |
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DISCARD = object() |
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class Pattern(tuple): |
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"""A matcher that binds a value to a name. |
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A ``Pattern`` can be indexed with another matcher to produce an |
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``AsPattern``. When matched with a value, an ``AsPattern`` both binds the |
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value to the name, and uses the matcher to match the value, thereby |
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constraining it to have a particular shape, and possibly introducing |
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further bindings. |
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""" |
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__slots__ = () |
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def __new__(cls, name: str): |
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if name == "_": |
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return DISCARD |
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if not name.isidentifier(): |
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raise ValueError |
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if keyword.iskeyword(name): |
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raise ValueError |
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return super().__new__(cls, (sys.intern(name),)) # type: ignore |
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@property |
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def name(self) -> str: |
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"""Return the name of the matcher.""" |
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return tuple.__getitem__(self, 0) |
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def __getitem__(self, other) -> typing.Union[Pattern, AsPattern]: |
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return AsPattern.bind(self, other) |
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class AsPattern(CompoundMatch, tuple): |
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"""A matcher that contains further bindings.""" |
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__slots__ = () |
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def __new__(cls, pattern: Pattern, structure): |
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return super().__new__(cls, (pattern, structure)) # type: ignore |
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@classmethod |
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def bind(cls, pattern: Pattern, structure) -> typing.Union[Pattern, AsPattern]: |
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if structure is DISCARD: |
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return pattern |
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return cls(pattern, structure) |
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@property |
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def pattern(self) -> Pattern: |
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"""Return the left-hand-side of the as-match.""" |
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return self[0] |
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@property |
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def structure(self): |
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"""Return the right-hand-side of the as-match.""" |
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return self[1] |
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68
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def destructure(self, value): |
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"""Return a tuple of sub-values to check. |
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By default, return the value twice. |
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If ``isinstance(value, AsPattern)``, return two values: |
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First, the structure to match against. |
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Second, by default, the value itself, but if ``value is self``, |
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instead return the pattern to bind to. |
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The behavior of returning the full AsPattern when ``value is not self`` |
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is present because it makes it possible to sensically use an AsPattern |
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as a target, which I don't know if there's a good reason for, but it |
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was easy to implement. |
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""" |
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if isinstance(value, AsPattern): |
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# Letting mutmut touch this line thoroughly locked things up. |
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if value is self: # pragma: no mutate |
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return (self.structure, self.pattern) |
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return (value.structure, value) |
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return (value, value) |
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mwchase /
python-structured-data
