Rick van Hattem
72 lines
2.3 KiB
Python
72 lines
2.3 KiB
Python
import inspect
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class Dataclass(type):
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def _get_signature(namespace):
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# Get the annotations from the class
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annotations = namespace.get('__annotations__', dict())
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# Signatures are immutable so we need to build the
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# parameter list before creating the signature
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parameters = []
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for name, annotation in annotations.items():
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# Create Parameter shortcut for readability
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Parameter = inspect.Parameter
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# Create the parameter with the correct type
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# annotation and default. You could also choose to
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# make the arguments keyword/positional only here
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parameters.append(Parameter(
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name=name,
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kind=Parameter.POSITIONAL_OR_KEYWORD,
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default=namespace.get(name, Parameter.empty),
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annotation=annotation,
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))
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return inspect.Signature(parameters)
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def _create_init(namespace, signature):
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# If init exists we don't need to do anything
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if '__init__' in namespace:
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return
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# Create the __init__ method and use the signature to
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# process the arguments
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def __init__(self, *args, **kwargs):
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bound = signature.bind(*args, **kwargs)
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bound.apply_defaults()
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for key, value in bound.arguments.items():
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# Convert to the annotation to enforce types
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parameter = signature.parameters[key]
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# Set the casted value
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setattr(self, key, parameter.annotation(value))
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# Override the signature for __init__ so help() works
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__init__.__signature__ = signature
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namespace['__init__'] = __init__
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def _create_repr(namespace, signature):
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def __repr__(self):
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arguments = []
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for key, value in vars(self).items():
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arguments.append(f'{key}={value!r}')
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arguments = ', '.join(arguments)
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return f'{self.__class__.__name__}({arguments})'
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namespace['__repr__'] = __repr__
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def __new__(metaclass, name, bases, namespace):
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signature = metaclass._get_signature(namespace)
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metaclass._create_init(namespace, signature)
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metaclass._create_repr(namespace, signature)
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cls = super().__new__(metaclass, name, bases, namespace)
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return cls
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