61 lines
1.9 KiB
Python
61 lines
1.9 KiB
Python
"""A registry for finding classes based on tags in the class."""
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class TagRegistry(object):
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"""
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A registry mapping tags to handlers.
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(A dictionary with some extra error checking.)
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"""
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def __init__(self):
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self._mapping = {}
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def register(self, cls):
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"""
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Register cls as a supported tag type. It is expected to define cls.tags as a list of tags
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that it implements.
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If an already-registered type has registered one of those tags, will raise ValueError.
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If there are no tags in cls.tags, will also raise ValueError.
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"""
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# Do all checks and complain before changing any state.
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if len(cls.tags) == 0:
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raise ValueError("No tags specified for class {0}".format(cls.__name__))
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for tag in cls.tags:
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if tag in self._mapping:
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other_cls = self._mapping[tag]
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if cls == other_cls:
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# registering the same class multiple times seems silly, but ok
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continue
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raise ValueError(
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"Tag {0} already registered by class {1}."
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" Can't register for class {2}".format(
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tag,
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other_cls.__name__,
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cls.__name__,
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)
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)
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# Ok, should be good to change state now.
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for t in cls.tags:
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self._mapping[t] = cls
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# Returning the cls means we can use this as a decorator.
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return cls
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def registered_tags(self):
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"""
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Get a list of all the tags that have been registered.
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"""
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return list(self._mapping.keys())
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def get_class_for_tag(self, tag):
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"""
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For any tag in registered_tags(), returns the corresponding class. Otherwise, will raise
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KeyError.
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"""
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return self._mapping[tag]
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