回的四种写法

# method 1
          # 采用异常捕捉来处理KeyError
          # 查询1次
          try:
              v = data[k]
          except KeyError:
              v = 12
          
          # method 2
          # 取值前先进行条件判断
          # 查询2次
          if data.has_key(k):
              v = data[k]
          else:
              v = 12
          
          # method 3
          # 和method2类似，只是利用in取代函数调用
          # 查询2次
          if k in data:
              v = data[k]
          else:
              v = 12
          
          # method 4
          # 函数调用
          # 查询1次
          v = data.get(k)
          if v == None:
              v = 12
          

#!/usr/bin/env python
          #-*- coding:utf-8 -*-
          import time, json
          
          def test(data, k, count):
              times = []
          
              start = time.time()
              for i in range(count):
                  #method 1
                  try:
                      v = data[k]
                  except KeyError:
                      v = 12
              end = time.time()
              print "method 1 spend time: %f s." % (end - start)
              times.append(end - start)
          
              start = time.time()
              for i in range(count):
                  #method 2
                  if data.has_key(k):
                      v = data[k]
                  else:
                      v = 12
              end = time.time()
              print "method 2 spend time: %f s." % (end - start)
              times.append(end - start)
          
              start = time.time()
              for i in range(count):
                  #method 3
                  if k in data:
                      v = data[k]
                  else:
                      v = 12
              end = time.time()
              print "method 3 spend time: %f s." % (end - start)
              times.append(end - start)
          
              start = time.time()
              for i in range(count):
                  #method 4
                  v = data.get(k)
                  if v == None:
                      v = 12
              end = time.time()
              print "method 4 spend time: %f s." % (end - start)
              times.append(end - start)
          
              return times
          
          def main():
              print "test hit"
              data = {'a': 12}
              k = 'a'
              times1 = test(data, k, 1000000)
              print
          
              print "test not hit"
              data = {'a': 12}
              k = 'ab'
              times2 = test(data, k, 1000000)
              print
          
              print "test data IO"
              data = {'a': 12}
              k = 'a'
              fd = FileDict(data)
              times3 = test(fd, k, 5000)
              print
          
              import numpy as np
              import matplotlib.pyplot as plt
          
              ind = np.arange(4)
              p1 = plt.bar(ind, times1, width=0.2, color='r')
              p2 = plt.bar(ind+0.2, times2, width=0.2, color='g')
              p3 = plt.bar(ind+0.4, times3, width=0.2, color='b')
              plt.xticks(ind, ('method 1', 'method 2', 'method 3', 'method 4') )
              plt.legend( (p1[0], p2[0], p3[0]), ('hit', 'not hit', 'IO') )
              plt.show()
          
          class FileDict:
              def __init__(self, data):
                  open('temp.txt','w').write(json.dumps(data))
          
              def get(self, key):
                  return json.load(open('temp.txt'))[key]
              __getitem__ = get
          
              def has_key(self, key):
                  return json.load(open('temp.txt')).has_key(key)
              __contains__ = has_key
          
          if __name__=="__main__":
              main()