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1from config import AWS_KEY, SECRET_KEY
2from amazonproduct import API
3
4import os
5from StringIO import StringIO
6
7try: # make it python2.4 compatible!
8    from hashlib import md5
9except ImportError: # pragma: no cover
10    from md5 import new as md5
11
12class ResponseCachingAPI (API):
13
14    CACHEDIR = 'cache'
15
16    def _fetch(self, url):
17        """
18        Monkey patch for the _fetch method of amazon API.
19        Preserve url of the last call and cache response into the file
20        (no cache invalidation yet)
21        """
22        self._last_url = url
23
24        if self.enable_cache:
25            path = os.path.join(self.CACHEDIR, self._cachename)
26            if os.path.isfile(path):
27                print 'Reading response from %s...' % path
28                f = open(path, 'r')
29                return f
30        
31        print 'Fetching response from %s...' % url
32        resp = StringIO(API._fetch(self, url).read())
33        
34        if self.enable_cache:
35            print 'Storing response in %s...' % path
36            f = open(path, 'w+')
37            f.write(resp.read())
38            resp.seek(0)
39            f.close()
40
41        return resp
42
43    def __init__(self, access_key_id, secret_access_key, locale,
44                 associate_tag=None, processor=None, enable_cache=True):
45        """
46        Monkey patch for the __init__ method of amazon API
47        Takes one more param, enable_cache and store it and tries to create
48        cache dir if needed
49        """
50        API.__init__(self, access_key_id, secret_access_key, locale,
51                     associate_tag, processor)
52
53        self.enable_cache = enable_cache
54        if self.enable_cache and not os.path.isdir(self.CACHEDIR):
55            os.mkdir(self.CACHEDIR)
56
57    def _build_url(self, **qargs):
58        """
59        Saving hash of meaningful part of the url to use it as cache key
60        """
61        url = API._build_url(self, **qargs)
62        cachename = "&".join([chunk for chunk in url.split('&') \
63            if chunk.find('Timestamp') != 0 and chunk.find('Signature') != 0])
64            
65        m = md5()
66        m.update(cachename)
67        self._cachename = m.hexdigest()
68            
69        return url
70
71if __name__ == '__main__':    
72    api = ResponseCachingAPI(AWS_KEY, SECRET_KEY, 'de')
73    api.item_search('Books', Author='Terry Pratchett')
74    api.item_search('Books', Author='Terry Pratchett')