flatisfy/flatisfy/filters/cache.py

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