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"""Utilities for destructuring values using matchables and match targets. |
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Given a value to destructure, called ``value``: |
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- Construct a matchable: ``matchable = Matchable(value)`` |
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- The matchable is initially falsy, but it will become truthy if it is passed a |
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**match target** that matches ``value``: |
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``assert matchable(some_pattern_that_matches)`` (Matchable returns itself |
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from the call, so you can put the calls in an if-elif block, and only make a |
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given call at most once.) |
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- When the matchable is truthy, it can be indexed to access bindings created by |
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the target. |
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""" |
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import collections |
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import operator |
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import typing |
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from ._attribute_constructor import AttributeConstructor |
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from ._destructure import DESTRUCTURERS |
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from ._match_failure import MatchFailure |
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from ._not_in import not_in |
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from ._patterns.basic_patterns import DISCARD |
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from ._patterns.basic_patterns import Pattern |
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from ._patterns.bind import Bind |
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from ._patterns.guard import Guard |
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from ._patterns.mapping_match import AttrPattern |
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from ._patterns.mapping_match import DictPattern |
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from ._stack_iter import Action |
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from ._stack_iter import Extend |
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from ._stack_iter import Yield |
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from ._stack_iter import stack_iter |
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def names(target) -> typing.List[str]: |
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"""Return every name bound by a target.""" |
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return DESTRUCTURERS.names(target) |
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def _as_name(key): |
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if isinstance(key, Pattern): |
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return key.name |
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return key |
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def _multi_index(dct, key): |
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if isinstance(key, tuple): |
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return tuple(dct[sub_key] for sub_key in key) |
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if isinstance(key, dict): |
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return {name: dct[value] for (name, value) in key.items()} |
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raise KeyError(key) |
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class MatchDict(collections.abc.MutableMapping): |
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def __init__(self) -> None: |
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self.data: typing.Dict[str, typing.Any] = {} |
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def __getitem__(self, key): |
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key = _as_name(key) |
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if isinstance(key, str): |
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return self.data[key] |
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return _multi_index(self, key) |
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def __setitem__(self, key, value): |
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key = _as_name(key) |
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if not isinstance(key, str): |
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raise TypeError |
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self.data[key] = value |
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def __delitem__(self, key): |
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del self.data[_as_name(key)] |
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def __iter__(self): |
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yield from self.data |
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def __len__(self): |
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return len(self.data) |
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80
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def _stack_iteration(item) -> typing.Optional[Action]: |
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target, value = item |
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if target is DISCARD: |
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return |
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if isinstance(target, Pattern): |
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return Yield((target, value)) |
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destructurer = DESTRUCTURERS.get_destructurer(target) |
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if destructurer: |
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return Extend(zip(destructurer(target), destructurer(value))) |
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elif target != value: |
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raise MatchFailure |
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92
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93
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def _match(target, value) -> MatchDict: |
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match_dict = MatchDict() |
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for target, value in stack_iter((target, value), _stack_iteration): |
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not_in(match_dict, target.name) |
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match_dict[target.name] = value |
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return match_dict |
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101
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class Matchable: |
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"""Given a value, attempt to match against a target.""" |
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104
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def __init__(self, value): |
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self.value = value |
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self.matches = None |
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108
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def match(self, target) -> "Matchable": |
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"""Match against target, generating a set of bindings.""" |
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try: |
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self.matches = _match(target, self.value) |
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except MatchFailure: |
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self.matches = None |
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return self |
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116
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def __call__(self, target): |
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return self.match(target) |
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119
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def __getitem__(self, key): |
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if self.matches is None: |
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raise ValueError |
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return self.matches[key] |
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123
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124
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def __bool__(self): |
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return self.matches is not None |
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126
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127
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128
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pat = AttributeConstructor(Pattern) |
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129
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130
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TRUTHY = Guard(operator.truth) |
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131
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FALSY = Guard(operator.not_) |
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132
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133
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134
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__all__ = [ |
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135
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"AttrPattern", |
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"Bind", |
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137
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"DictPattern", |
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"FALSY", |
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"Guard", |
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"Matchable", |
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"Pattern", |
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"TRUTHY", |
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"names", |
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"pat", |
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] |
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mwchase /
python-structured-data
