79 lines
2.1 KiB
Python
79 lines
2.1 KiB
Python
# Copyright 2017 Massachusetts Open Cloud
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import uuid
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class CachedProperty(object):
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"""A decorator that converts a function into a lazy property.
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Taken from : https://github.com/nshah/python-memoize
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The function wrapped is called the first time to retrieve the result
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and then that calculated result is used the next time you access
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the value:
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class Foo(object):
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@CachedProperty
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def bar(self):
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# calculate something important here
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return 42
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"""
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def __init__(self, func, name=None, doc=None):
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self.func = func
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self.__name__ = name or func.__name__
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self.__doc__ = doc or func.__doc__
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def __get__(self, obj, owner):
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if obj is None:
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return self
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value = self.func(obj)
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setattr(obj, self.__name__, value)
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return value
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def safe_get(a, i, default=None):
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"""Return the i-th element if it exists, or default."""
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try:
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return a[i]
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except IndexError:
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return default
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def safe_pop(a, i=0, default=None):
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"""Pops the i-th element, if any, otherwise returns default"""
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try:
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return a.pop(i)
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except (IndexError, KeyError):
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return default
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def is_uuid(value):
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"""Return true if value is a valid uuid."""
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try:
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uuid.UUID(value, version=4)
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return True
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except (ValueError, TypeError):
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return False
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def pop_if_uuid(a):
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"""Pops the first element of the list only if it is a uuid."""
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if is_uuid(safe_get(a, 0)):
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return safe_pop(a)
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else:
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return None
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