Patch for python implementation of amazonproduct API to enable caching and preserve some debug info.

amazonproduct_patch.py

from amazonproduct import API
import os
from hashlib import md5


old_fetch = API._fetch
old_build_url = API._build_url
old_init = API.__init__

def new_fetch(self, url):
    """
    Monkey patch for the _fetch method of amazon API.
    Preserve url of the last call  and cache response into the file
    (no cache invalidation yet)
    """
    self._last_url = url

    if self.enable_cache:
        path = os.path.join(self.CACHEDIR, self._cachename)
        if os.path.isfile(path):
            f = open(path, 'r')
            return f
    
    resp = old_fetch(self, url)
    
    if self.enable_cache:
        f = open(path, 'w+')
        f.write(resp.read())
        resp.seek(0)
        f.close()

    return resp

def new_init(self, access_key_id, secret_access_key, locale,
             associate_tag=None, processor=None, enable_cache=True):
    """
    Monkey patch for the __init__ method of amazon API
    Takes one more param, enable_cache and store it and tries to create
    cache dir if needed
    """
    self.enable_cache = enable_cache

    if self.enable_cache and not os.path.isdir(self.CACHEDIR):
        os.mkdir(self.CACHEDIR)

    return old_init(self, access_key_id, secret_access_key, locale,
                    associate_tag, processor)
                    
def new_build_url(self, **qargs):
    """
    Saving hash of meaningful part of the url to use it as cache key
    """
    url = old_build_url(self, **qargs)
    cachename = "&".join([chunk for chunk in url.split('&') \
        if chunk.find('Timestamp') != 0 and chunk.find('Signature') != 0])
        
    m = md5()
    m.update(cachename)
    self._cachename = m.hexdigest()
        
    return url

API.CACHEDIR = 'cache'
    
API._fetch = new_fetch
API.__init__ = new_init
API._build_url = new_build_url