[Google App Engine][Python]Amazon Product Advertising APIをリファクタリング

ちょこちょこ作り続けているGoogle App EngineのPythonでAmazon Product Advertising APIをコールするクラスですが、itemsearchとitemlookupで同じ処理が2回呼ばれている部分があり保守性が悪かったので下記のようにリファクタリングしました。

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright 2007 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

from urlparse import urlparse
from google.appengine.api import urlfetch
from lxml import etree

import os
import urllib
import datetime
import hashlib
import base64
import logging
import hmac
import xmltodict

class AmazonProductAdvertisingAPI(object):
  def __init__(self,access_key_id,secret_access_key,associate_tag = None,locale = "US"):

    self._access_key_id = access_key_id
    self._secret_access_key = secret_access_key
    self._associate_tag = associate_tag

    self._validate_certificate = True
    _environ = os.environ
    _http_host = _environ["HTTP_HOST"]
    if _http_host.find("localhost") > -1:
      self._validate_certificate = False

    _wsgi_url_scheme = _environ["wsgi.url_scheme"]
    self._endpoint = {
      "JP":_wsgi_url_scheme + "://webservices.amazon.co.jp/onca/xml",
      "US":_wsgi_url_scheme + "://webservices.amazon.com/onca/xml",
      "FR":_wsgi_url_scheme + "://webservices.amazon.fr/onca/xml",
      "IN":_wsgi_url_scheme + "://webservices.amazon.in/onca/xml",
      "IT":_wsgi_url_scheme + "://webservices.amazon.it/onca/xml",
      "UK":_wsgi_url_scheme + "://webservices.amazon.co.uk/onca/xml"
    }

    if self._endpoint.has_key(locale):
      self._product_advertising_url = self._endpoint[locale]
    else:
      self._product_advertising_url = self._endpoint["US"]

    self._service = "AWSECommerceService"

    #self._method = ""
    #self._prms = {}

  #タイムスタンプを設定
  def _timestamp(self,prms):

    prms["Timestamp"] = datetime.datetime.utcnow().strftime("%Y-%m-%dT%H:%M:%SZ")

  #URLエンコード
  def _urlencode_rfc3986(self,s):
    _s = urllib.quote(s)
    _s = _s.replace("%7E", "~")
    return _s

  #アクセストークン用の文字列作成
  def _canonical_string(self,prms):

    _keys = sorted(prms)
    _canonical_string = ""
    for _k in _keys:
      _canonical_string = _canonical_string + "&" + self._urlencode_rfc3986(_k) + "=" + self._urlencode_rfc3986(prms[_k])
    else:
      _canonical_string = _canonical_string[1:]

    return _canonical_string

  #問い合わせURLの作成
  def _request_url(self,prms,method):

    _url_info = urlparse(self._product_advertising_url)

    _canonical_string = self._canonical_string(prms)

    _signature = method + "\n" + _url_info.hostname + "\n" + _url_info.path +"\n" + _canonical_string
    _signature = hmac.new(self._secret_access_key, _signature, hashlib.sha256).digest()
    _signature = base64.b64encode(_signature)

    _url = self._product_advertising_url + "?" + _canonical_string + "&Signature=" + self._urlencode_rfc3986(_signature)

    return _url

  #itemsearch
  def itemsearch(self,searchindex,browsenode=None,availability="Available",responsegroup="Small",itempage=1,keywords=None,minimumprice=None,maximumprice=None,isremoveadult=True,sort=None):

    _prms = {}

    _prms["Service"] = self._service
    _prms["AWSAccessKeyId"] = self._access_key_id

    if self._associate_tag is not None:
      _prms["AssociateTag"] = self._associate_tag

    _prms["Operation"] = "ItemSearch"
    self._timestamp(_prms)
    
    if availability is None:
      return None

    for i in ["Available"]:
      if i == availability:
        _prms["Availability"] = availability
        break
    else:
      return None

    if searchindex is None:
      return None

    if searchindex == u"":
      return None

    _prms["SearchIndex"] = searchindex

    if responsegroup is None:
      return None

    if responsegroup == "":
      return None

    _prms["ResponseGroup"] = responsegroup

    if browsenode is not None:
      _prms["BrowseNode"] = browsenode

    if itempage is not None:
      _prms["ItemPage"] = str(itempage)

    if keywords is not None:
      #logging.info()
      if isinstance(keywords,unicode):
        #logging.info(keywords)
        _prms["Keywords"] = keywords.encode('utf-8')
      else:
        _prms["Keywords"] = keywords
      #_prms["Keywords"] = keywords

    if maximumprice is not None:
      _prms["MaximumPrice"] = str(maximumprice)

    if minimumprice is not None:
      _prms["MinimumPrice"] = str(minimumprice)

    if sort is not None:
      _prms["Sort"] = sort


    _url = self._request_url(_prms,"GET")
    #logging.info(_url)
    _result = self._request(_url)
    return _result

  #itemlookup
  def itemlookup(self,asin,responsegroup="Small"):
    _prms = {}

    _prms["Service"] = self._service
    _prms["AWSAccessKeyId"] = self._access_key_id

    if self._associate_tag is not None:
      _prms["AssociateTag"] = self._associate_tag

    _prms["Operation"] = "ItemLookup"
    self._timestamp(_prms)

    if asin is None:
      return None

    if asin == "":
      return None

    _prms["ItemId"] = asin

    if responsegroup is None:
      return None

    if responsegroup == "":
      return None

    _prms["ResponseGroup"] = responsegroup

    _url = self._request_url(_prms,"GET")
    _result = self._request(_url)
    return _result

  def _request(self,url):
    try:
      _result = urlfetch.fetch(url,validate_certificate = self._validate_certificate)
      _status_code = _result.status_code
      #logging.info(_status_code)

      if _status_code == 200:

        _content = _result.content
        _root = etree.fromstring(_content)
        _ns = _root.xpath('namespace-uri(.)')
        _namespace = {"ns":_ns}
        _errorTags = _root.findall('.//ns:Error',namespaces=_namespace)
        #logging.info(_content)
        if len(_errorTags) > 0:
          _errorTag = _errorTags[0]
          _code  = _errorTag.findall('.//ns:Code',namespaces=_namespace)
          _message = _errorTag.findall('.//ns:Message',namespaces=_namespace)
          logging.error(u"code: " + _code[0].text + " message: " + _message[0].text)
        else:
          return _root
      else:
        logging.error(u"status code: " + str(_status_code) + " content:" + _content)
        
    except urlfetch.DeadlineExceededError:
      logging.error(u"urlfetch DeadlineExceededError")

    except urlfetch.ResponseTooLargeError, response:
      logging.error(u"urlfetch ResponseTooLargeError" + response)

    except urlfetch.InternalTransientError:
      logging.error(u"urlfetch InternalTransientError")

    except urlfetch.InvalidURLError:
      logging.error(u"urlfetch InvalidURLError")

    except urlfetch.Error:
      logging.error(u"urlfetch Error")

    return None