89 lines
2.2 KiB
Python
89 lines
2.2 KiB
Python
# coding: utf-8
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"""
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Caching function for pictures.
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"""
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from __future__ import absolute_import, print_function, unicode_literals
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import requests
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class MemoryCache(object):
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"""
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A cache in memory.
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"""
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@staticmethod
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def on_miss(key):
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"""
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Method to be called whenever an object is requested from the cache but
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was not already cached. Typically, make a HTTP query to fetch it.
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:param key: Key of the requested object.
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:return: The object content.
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"""
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raise NotImplementedError
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def __init__(self):
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self.hits = 0
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self.misses = 0
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self.map = {}
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def get(self, key):
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"""
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Get an element from cache. Eventually call ``on_miss`` if the item is
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not already cached.
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:param key: Key of the element to retrieve.
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:return: Requested element.
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"""
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cached = self.map.get(key, None)
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if cached is not None:
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self.hits += 1
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return cached
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item = self.map[key] = self.on_miss(key)
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self.misses += 1
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return item
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def total(self):
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"""
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Get the total number of calls (with hits to the cache, or miss and
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fetching with ``on_miss``) to the cache.
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:return: Total number of item accessing.
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"""
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return self.hits + self.misses
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def hit_rate(self):
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"""
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Get the hit rate, that is the rate at which we requested an item which
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was already in the cache.
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:return: The hit rate, in percents.
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"""
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assert self.total() > 0
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return 100 * self.hits // self.total()
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def miss_rate(self):
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"""
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Get the miss rate, that is the rate at which we requested an item which
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was not already in the cache.
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:return: The miss rate, in percents.
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"""
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assert self.total() > 0
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return 100 * self.misses // self.total()
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class ImageCache(MemoryCache):
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"""
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A cache for images, stored in memory.
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"""
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@staticmethod
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def on_miss(url):
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"""
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Helper to actually retrieve photos if not already cached.
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"""
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return requests.get(url)
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