Python - How to update a multi-dimensional dict

Question

Follow up of my previous question: http://stackoverflow.com/questions/3680464/python-how-to-recursively-add-a-folders-content-in-a-dict.

When I build the information dict for each file and folder, I need to merge it to the main tree dict. The only way I have found so far is the write the dict as a text string and have it interpreted into a dict object and then merge it. The issue is that the root object is always the same so it gets overwritten by the new dict and I lose the content.

def recurseItem(Files, Item):
    global Settings
    ROOT = Settings['path']
    dbg(70, "Scanning " + Item)
    indices = path2indice(Item)
    ItemAnalysis = Analyse(Item)
    Treedict = ""#{'" + ROOT + "': "
    i=0
    for indice in indices:
        Treedict = Treedict + "{'" + indice + "': "
        i=i+1
    Treedict = Treedict + repr(ItemAnalysis)
    while i>0:
        Treedict = Treedict + "}"
        i=i-1
    Files = dict(Files.items() + Treedict.items())
return Files

Is there a way to avoid the messy indices construct (i.e. Files[ROOT][fileName][fileName2][fileName3][fileName4] ) which can't be generated on the fly? I need to be able to update a key's content without overwriting the root key. Any idea would be much welcomed !

Answer 1

I'm not entirely sure I understand what you're asking for, but it seems like a textbook case for recursion. I think something like this might be of use (as a replacement for your current method):

import os

FILES = ...
def process(directory):
    dir_dict = {}
    for file in os.listdir(directory):
        filename = os.path.join(directory, file)
        if os.path.isdir(file):
            dir_dict[file] = process(filename)
        else: # assuming it needs to be processed as a file
            dir_dict[file] = Analyse(filename)
    return dir_dict

(based on phihag's answer to your other question) Basically this constructs a dict for each directory containing the analyzed information about the files in that directory, and inserts that dict into the dict for the parent directory.

If it's not this, I think dict.update and/or the collections.defaultdict class may need to be involved.

Answer 2

Of course you can create nested dictionaries on-the-fly. What about this:

# Example path, I guess something like this is produced by path2indice?!
indices = ("home", "username", "Desktop")

tree = {}

d = tree
for indice in indices[:-1]:
    if indice not in d:
        d[indice] = {}

    d = d[indice]

d[indices[-1]] = "some value"

print tree # this will print {'home': {'username': {'Desktop': 'some value'}}}