Question

您好我有以下代码。当我运行getDetails函数时，尝试：确实有效，但异常无法正常显示。

data_dict = {}
dict_list = []
def createNameDict(filename):
  path = "C:\Users\user\Desktop"
  basename = "ParkingData_Part2.txt"
  filename = path + "//" + basename
  file = open(filename)
  contents = file.read()
  print contents,"\n"


  data_list = [lines.split(",") for lines in contents.split("\n")]



  for line in data_list:
    regNumber = line[0]
    details = (line[1],line[2],line[3])

    data_dict[regNumber] = details
  print data_dict,"\n"
  print data_dict.items(),"\n"

def getDetails(regNumber):
  #if regNumber in data_dict: 
    try:
      if regNumber in data_dict:
        print data_dict[regNumber]

        #print data_dict.get(regNumber)
    except:
      printNow(regNumber, "not in dictionary")
    return
def addRegistration(regNumber, details):
  try:
     data_dict[regNumber] = details


  except:
    print regNumber, "Key Already exist"

 #data_dict.update({regNumber:(details)})
  return data_dict

我的输出是：

======= Loading Progam =======
>>> createNameDict("C:\Users\user\Desktop//ParkingData_Part2.txt")
EDF768, Bill Meyer, 2456, Vet_Parking
TY5678, Jane Miller, 8987, AgHort_Parking
GEF123, Jill Black, 3456, Creche_Parking
ABC234, Fred Greenside, 2345, AgHort_Parking
GH7682, Clara Hill, 7689, AgHort_Parking
JU9807, Jacky Blair, 7867, Vet_Parking
KLOI98, Martha Miller, 4563, Vet_Parking
ADF645, Cloe Freckle, 6789, Vet_Parking
DF7800, Jacko Frizzle, 4532, Creche_Parking
WER546, Olga Grey, 9898, Creche_Parking
HUY768, Wilbur Matty, 8912, Creche_Parking 

{'HUY768': (' Wilbur Matty', ' 8912', ' Creche_Parking'), 'GH7682': (' Clara Hill', ' 7689', ' AgHort_Parking'), 'GEF123': (' Jill Black', ' 3456', ' Creche_Parking'), 'WER546': (' Olga Grey', ' 9898', ' Creche_Parking'), 'TY5678': (' Jane Miller', ' 8987', ' AgHort_Parking'), 'ABC234': (' Fred Greenside', ' 2345', ' AgHort_Parking'), 'KLOI98': (' Martha Miller', ' 4563', ' Vet_Parking'), 'EDF768': (' Bill Meyer', ' 2456', ' Vet_Parking'), 'JU9807': (' Jacky Blair', ' 7867', ' Vet_Parking'), 'DF7800': (' Jacko Frizzle', ' 4532', ' Creche_Parking'), 'ADF645': (' Cloe Freckle', ' 6789', ' Vet_Parking')} 

[('HUY768', (' Wilbur Matty', ' 8912', ' Creche_Parking')), ('GH7682', (' Clara Hill', ' 7689', ' AgHort_Parking')), ('GEF123', (' Jill Black', ' 3456', ' Creche_Parking')), ('WER546', (' Olga Grey', ' 9898', ' Creche_Parking')), ('TY5678', (' Jane Miller', ' 8987', ' AgHort_Parking')), ('ABC234', (' Fred Greenside', ' 2345', ' AgHort_Parking')), ('KLOI98', (' Martha Miller', ' 4563', ' Vet_Parking')), ('EDF768', (' Bill Meyer', ' 2456', ' Vet_Parking')), ('JU9807', (' Jacky Blair', ' 7867', ' Vet_Parking')), ('DF7800', (' Jacko Frizzle', ' 4532', ' Creche_Parking')), ('ADF645', (' Cloe Freckle', ' 6789', ' Vet_Parking'))] 

>>> getDetails("GFT245")

>>> getDetails("HUY768")

(' Wilbur Matty', ' 8912', ' Creche_Parking')
>>> getDetails("JU9807")

(' Jacky Blair', ' 7867', ' Vet_Parking')

>>> getDetails("GH7682")

(' Clara Hill', ' 7689', ' AgHort_Parking')
>>>

如果GFT245不在词典中，它应该显示 GFT245不在字典中但是当我执行程序

时它不会那样

Answer 1

问题出在这里：

if regNumber in data_dict:
    print data_dict[regNumber]

当您询问字典中是否存在regNumber时，由于regNumber不存在而您不会尝试对其进行索引，因此永远不会引发异常，因此不会引发KeyError例外。

如果您想要引发异常，那么只需执行：

print data_dict[regNumber]

Answer 2

在您的getDetails函数中，except部分永远不会触发，因为您在访问之前明确检查密钥是否在字典中，您可能希望将其重写为

if key in dict:
    # The key exists and do something
else:
    # The key doesn't exist, notify the user

或

try:
    print dict[key]
except KeyError:
    # The key doesn't exist, notify the user

我更喜欢第一种的样式，因为异常是昂贵的，当然如果你知道你只有少量的字典中不存在的键并且会导致异常，那么你可以优化第二种方式

应重新编写addRegistration函数以测试密钥是否已存在并通知用户，否则添加数据，因为如果密钥已存在，它将不会发出警告或引发异常，只会更新/替换该密钥的数据。

Answer 3

if regNumber in data_dict:
  print data_dict[regNumber]

在访问data_dict之前，您有条件。如果regNumber不在dict，那么它就不会尝试访问它。因此没有抛出异常。

Answer 4

def getDetails(regNumber):
  #if regNumber in data_dict: 
    try:
      if regNumber in data_dict:
        print data_dict[regNumber]

        #print data_dict.get(regNumber)
    except:
      printNow(regNumber, "not in dictionary")
    return

try块中没有任何内容实际上失败。

为什么呢？由于if regNumber in data_dict测试。如果代码不在字典中，它将永远不会尝试查找它。

也许你的意思是：

def getDetails(regNumber):
    if regNumber in data_dict:
        print data_dict[regNumber]
    else:
        printNow(regNumber, "not in dictionary")

Answer 5

问题是

try:
  if regNumber in data_dict:
    print data_dict[regNumber]

    #print data_dict.get(regNumber)
except:
  printNow(regNumber, "not in dictionary")

如果regNumber不在data_dict，则不会发生异常。将其更改为：

try:
    print data_dict[regNumber]
except:
  printNow(regNumber, "not in dictionary")

尝试，除了不工作

5 个答案: