CODEWITHSUNDEEP
python
SRC
SRC

Reputation: 2271

append in a list causing value overwrite

I am facing a peculiar problem. I will describe in brief bellow Suppose i have this piece of code -

class MyClass:

   __postBodies = []
    .
    .
    .
for the_file in os.listdir("/dir/path/to/file"):
      file_path = os.path.join(folder, the_file)
      params = self.__parseFileAsText(str(file_path)) #reads the file and gets some parsed data back
      dictData = {'file':str(file_path), 'body':params}
      self.__postBodies.append(dictData)
      print self.__postBodies
      dictData = None
      params = None

Problem is, when i print the params and the dictData everytime for different files it has different values (the right thing), but as soon as the append occurs, and I print __postBodies a strange thing happens. If there are thee files, suppose A,B,C, then

first time __postBodies has the content = [{'body':{A dict with some data related to file A}, 'file':'path/of/A'}]

second time it becomes = [{'body':{A dict with some data relaed to file B}, 'file':'path/of/A'}, {'body':{A dict with some data relaed to file B}, 'file':'path/of/B'}]

AND third time = [{'body':{A dict with some data relaed to file C}, 'file':'path/of/A'}, {'body':{A dict with some data relaed to file C}, 'file':'path/of/B'}, {'body':{A dict with some data relaed to file C}, 'file':'path/of/C'}]

So, you see the 'file' key is working very fine. Just strangely the 'body' key is getting overwritten for all the entries with the one last appended.

Am i making any mistake? is there something i have to? Please point me to a direction.

Sorry if I am not very clear.

EDIT ------------------------

The return from self.__parseFileAsText(str(file_path)) call is a dict that I am inserting as 'body' in the dictData.

EDIT2 ----------------------------

as you asked, this is the code, but i have checked that params = self.__parseFileAsText(str(file_path)) call is returning a diff dict everytime.

def __parseFileAsText(self, fileName):

        i = 0
        tempParam = StaticConfig.PASTE_PARAMS

        tempParam[StaticConfig.KEY_PASTE_PARAM_NAME] = ""
        tempParam[StaticConfig.KEY_PASTE_PARAM_PASTEFORMAT] = "text"
        tempParam[StaticConfig.KEY_PASTE_PARAM_EXPIREDATE] = "N"
        tempParam[StaticConfig.KEY_PASTE_PARAM_PRIVATE] = ""
        tempParam[StaticConfig.KEY_PASTE_PARAM_USER] = ""
        tempParam[StaticConfig.KEY_PASTE_PARAM_DEVKEY] = ""
        tempParam[StaticConfig.KEY_PASTE_FORMAT_PASTECODE] = ""

        for line in fileinput.input([fileName]):
            temp = str(line)
            temp2 = temp.strip()
            if i == 0:              
                postValues = temp2.split("|||")

                if int(postValues[(len(postValues) - 1)]) == 0 or int(postValues[(len(postValues) - 1)]) == 2:
                    tempParam[StaticConfig.KEY_PASTE_PARAM_NAME] = str(postValues[0])

                    if str(postValues[1]) == '':                                        
                        tempParam[StaticConfig.KEY_PASTE_PARAM_PASTEFORMAT] = 'text'
                    else:
                        tempParam[StaticConfig.KEY_PASTE_PARAM_PASTEFORMAT] = postValues[1]

                    if str(postValues[2]) != "N":
                        tempParam[StaticConfig.KEY_PASTE_PARAM_EXPIREDATE] = str(postValues[2])

                    tempParam[StaticConfig.KEY_PASTE_PARAM_PRIVATE] = str(postValues[3])
                    tempParam[StaticConfig.KEY_PASTE_PARAM_USER] = StaticConfig.API_USER_KEY
                    tempParam[StaticConfig.KEY_PASTE_PARAM_DEVKEY] = StaticConfig.API_KEY

                else:
                    tempParam[StaticConfig.KEY_PASTE_PARAM_USER] = StaticConfig.API_USER_KEY
                    tempParam[StaticConfig.KEY_PASTE_PARAM_DEVKEY] = StaticConfig.API_KEY
                i = i+1
            else:
                if tempParam[StaticConfig.KEY_PASTE_FORMAT_PASTECODE] != "" :           
                    tempParam[StaticConfig.KEY_PASTE_FORMAT_PASTECODE] = str(tempParam[StaticConfig.KEY_PASTE_FORMAT_PASTECODE])+"\n"+temp2
                else:
                    tempParam[StaticConfig.KEY_PASTE_FORMAT_PASTECODE] = temp2

        return tempParam

Upvotes: 1

Views: 571

Answers (2)

Pierre GM
Pierre GM

Reputation: 20339

What if __postBodies wasn't a class attribute, as it is defined now, but just an instance attribute?

Upvotes: 0

Andrew Clark
Andrew Clark

Reputation: 208495

You are likely returning the same dictionary with every call to MyClass.__parseFileAsText(), a couple of common ways this might be happening:

  • __parseFileAsText() accepts a mutable default argument (the dict that you eventually return)
  • You modify an attribute of the class or instance and return that instead of creating a new one each time

Making sure that you are creating a new dictionary on each call to __parseFileAsText() should fix this problem.

Edit: Based on your updated question with the code for __parseFileAsText(), your issue is that you are reusing the same dictionary on each call:

tempParam = StaticConfig.PASTE_PARAMS
...
return tempParam

On each call you are modifying StaticConfig.PASTE_PARAMS, and the end result is that all of the body dictionaries in your list are actually references to StaticConfig.PASTE_PARAMS. Depending on what StaticConfig.PASTE_PARAMS is, you should change that top line to one of the following:

# StaticConfig.PASTE_PARAMS is an empty dict
tempParam = {}

# All values in StaticConfig.PASTE_PARAMS are immutable
tempParam = dict(StaticConfig.PASTE_PARAMS)

If any values in StaticConfig.PASTE_PARAMS are mutable, you could use copy.deepcopy but it would be better to populate tempParam with those default values on your own.

Upvotes: 2

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