wehub-resource-sync
53 lines
2.0 KiB
Python
53 lines
2.0 KiB
Python
from collections import defaultdict
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from typing import Any, Callable
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class LambdaDefaultDict(defaultdict):
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"""A defaultdict that creates default values based on the associated key.
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Note that the standard defaultdict can only produce default values (via its factory)
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that are independent of the key under which they are stored.
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As opposed to that, the lambda functions used as factories for this
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`LambdaDefaultDict` class do accept a single argument: The missing key.
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If a missing key is accessed by the user, the provided lambda function is called
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with this missing key as its argument. The returned value is stored in the
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dictionary under that key and returned.
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Example:
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In this example, if you try to access a key that doesn't exist, it will call
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the lambda function, passing it the missing key. The function will return a
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string, which will be stored in the dictionary under that key.
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.. testcode::
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from ray.rllib.utils.lambda_defaultdict import LambdaDefaultDict
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default_dict = LambdaDefaultDict(lambda missing_key: f"Value for {missing_key}")
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print(default_dict["a"])
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.. testoutput::
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Value for a
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""" # noqa: E501
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def __init__(self, default_factory: Callable[[str], Any], *args, **kwargs):
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"""Initializes a LambdaDefaultDict instance.
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Args:
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default_factory: The default factory callable, taking a string (key)
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and returning the default value to use for that key.
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"""
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if not callable(default_factory):
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raise TypeError("First argument must be a Callable!")
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# We will handle the factory in __missing__ method.
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super().__init__(None, *args, **kwargs)
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self.default_factory = default_factory
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def __missing__(self, key):
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# Call default factory with the key as argument.
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self[key] = value = self.default_factory(key)
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return value
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