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"""Base class for Sum subclasses and Product. |
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Blocks access to many built-in methods. |
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""" |
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import inspect |
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import typing |
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import weakref |
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from . import _annotations |
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_T = typing.TypeVar("_T") |
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def _should_include(name, static): |
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if name in SHADOWED_ATTRIBUTES and static is None: |
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return False |
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if isinstance(static, SumMember): |
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return False |
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return True |
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class ADTConstructor: |
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"""Base class for ADT Constructor classes.""" |
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__slots__ = () |
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def __dir__(self): |
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return [ |
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attribute |
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for attribute in super().__dir__() |
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if _should_include(attribute, inspect.getattr_static(self, attribute)) |
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] |
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__eq__ = object.__eq__ |
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__ne__ = object.__ne__ |
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__hash__ = object.__hash__ |
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SHADOWED_ATTRIBUTES = { |
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"__add__", |
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"__contains__", |
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"__getitem__", |
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"__iter__", |
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"__len__", |
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"__mul__", |
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"__rmul__", |
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"count", |
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"index", |
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"__lt__", |
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"__le__", |
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"__gt__", |
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"__ge__", |
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} |
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56
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for _attribute in SHADOWED_ATTRIBUTES: |
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setattr(ADTConstructor, _attribute, None) |
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60
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class SumMember: |
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"""Accessor for Sum subclass constructor, only accessible from the base.""" |
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def __init__(self, subcls: type): |
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self.subcls = subcls |
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def __get__(self, obj, cls): |
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if cls is ADT_BASES[self.subcls] and obj is None: |
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return self.subcls |
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raise AttributeError("Can only access adt members through base class.") |
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71
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72
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ADT_BASES: typing.MutableMapping[type, type] = weakref.WeakKeyDictionary() |
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74
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75
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def make_constructor(_cls, name: str, args: typing.Tuple, subclass_order): |
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"""Create a subclass of _cls with a constructor generated from args.""" |
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length = len(args) |
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79
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# pylint: disable=missing-docstring |
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class Constructor(_cls, ADTConstructor, tuple): # type: ignore |
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__doc__ = f"""Auto-generated subclass {name} of ADT {_cls.__qualname__}. |
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Takes {length} argument{'' if length == 1 else 's'}. |
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""" |
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86
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__slots__ = () |
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def __new__(cls, *args): |
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if len(args) != length: |
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raise ValueError |
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return super().__new__(cls, args) |
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93
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ADT_BASES[Constructor] = _cls |
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Constructor.__name__ = name |
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Constructor.__qualname__ = "{qualname}.{name}".format( |
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qualname=_cls.__qualname__, name=name |
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) |
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100
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setattr(_cls, name, SumMember(Constructor)) |
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subclass_order.append(Constructor) |
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103
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annotations = {f"_{index}": arg for (index, arg) in enumerate(args)} |
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parameters = [ |
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inspect.Parameter(name, inspect.Parameter.POSITIONAL_ONLY, annotation=arg) |
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for (name, arg) in annotations.items() |
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] |
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annotations["return"] = _cls.__qualname__ |
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110
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Constructor.__new__.__signature__ = inspect.Signature( # type: ignore |
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[inspect.Parameter("cls", inspect.Parameter.POSITIONAL_ONLY)] + parameters, |
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return_annotation=_cls.__qualname__, |
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) |
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Constructor.__new__.__annotations__ = annotations |
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115
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116
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117
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def make_constructors(cls): |
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118
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subclass_order: typing.List[typing.Type[_T]] = [] |
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119
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120
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for name, args in _annotations._sum_args_from_annotations(cls).items(): |
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make_constructor(cls, name, args, subclass_order) |
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122
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123
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return tuple(subclass_order) |
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125
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126
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__all__ = ["ADTConstructor", "make_constructor"] |
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mwchase /
python-structured-data
