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# -*- coding: utf-8 -*-
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# Natural Language Toolkit: JSON Encoder/Decoder Helpers
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#
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# Copyright (C) 2001-2020 NLTK Project
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# Author: Steven Xu <xxu@student.unimelb.edu.au>
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#
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# URL: <http://nltk.org/>
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# For license information, see LICENSE.TXT
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"""
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Register JSON tags, so the nltk data loader knows what module and class to look for.
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NLTK uses simple '!' tags to mark the types of objects, but the fully-qualified
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"tag:nltk.org,2011:" prefix is also accepted in case anyone ends up
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using it.
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"""
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import json
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json_tags = {}
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TAG_PREFIX = "!"
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def register_tag(cls):
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"""
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Decorates a class to register it's json tag.
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"""
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json_tags[TAG_PREFIX + getattr(cls, "json_tag")] = cls
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return cls
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class JSONTaggedEncoder(json.JSONEncoder):
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def default(self, obj):
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obj_tag = getattr(obj, "json_tag", None)
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if obj_tag is None:
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return super(JSONTaggedEncoder, self).default(obj)
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obj_tag = TAG_PREFIX + obj_tag
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obj = obj.encode_json_obj()
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return {obj_tag: obj}
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class JSONTaggedDecoder(json.JSONDecoder):
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def decode(self, s):
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return self.decode_obj(super(JSONTaggedDecoder, self).decode(s))
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@classmethod
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def decode_obj(cls, obj):
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# Decode nested objects first.
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if isinstance(obj, dict):
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obj = dict((key, cls.decode_obj(val)) for (key, val) in obj.items())
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elif isinstance(obj, list):
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obj = list(cls.decode_obj(val) for val in obj)
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# Check if we have a tagged object.
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if not isinstance(obj, dict) or len(obj) != 1:
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return obj
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obj_tag = next(iter(obj.keys()))
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if not obj_tag.startswith("!"):
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return obj
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if obj_tag not in json_tags:
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raise ValueError("Unknown tag", obj_tag)
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obj_cls = json_tags[obj_tag]
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return obj_cls.decode_json_obj(obj[obj_tag])
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__all__ = ["register_tag", "json_tags", "JSONTaggedEncoder", "JSONTaggedDecoder"]
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