Editing Pickled Data

I need to save a complex piece of data:

list = ["Animals", {"Cats":4, "Dogs":5}, {"x":[], "y":[]}]

I was planning on saving several of these lists within the same file, and I was also planning on using the pickle module to save this data. I also want to be able to access the pickled data and add items to the lists in the 2nd dictionary. So after I unpickle the data and edit, the list might look like this:

list = ["Animals", {"Cats":4, "Dogs":5}, {"x"=[1, 2, 3], "y":[]}]

Preferable, I want to be able to save this list (using pickle) in the same file I took that piece of data from. However, if I simply re-pickle the data to the same file (lets say I originally saved it to "File"), I'll end up with two copies of the same list in that file:

a = open("File", "ab")
pickle.dump(list, a)
a.close()

Is there a way to replace the edited list in the file using pickle rather than adding a second (updated) cop开发者_如何转开发y? Or, is there another method I should consider for saving this data?

I think you want the shelve module. It creates a file (uses pickle under the hood) that contains the contents of a variable accessible by key (think persistent dictionary).

You could open the file for writing instead of appending -- then the changes would overwrite previous data. This is however a problem if there is more data stored in that file. If what you want really is to selectively replace data in a pickled file, I'm afraid this won't work with pickle. If this is a common operation, check if something like a sqlite database helps you to this end.