Walking/iterating over a nested dictionary of arbitrary depth (the dictionary represents a directory tree)

Question

Python newbie at time of writing.

This came up because I want a user to be able to select a group of files from within a directory (and also any subdirectory), and unfortunately Tkinter's default ability for selecting multiple files in a file dialog is broken on Windows 7 (http://bugs.python.org/issue8010).

So I am attempting to represent a directory structure by an alternative method (still using Tkinter): constructing a facsimile of the directory structure, made of labeled and indented checkboxes (organized in a tree). So a directory like this:

\SomeRootDirectory
    \foo.txt
    \bar.txt
    \Stories
        \Horror
            \scary.txt
            \Trash
                \notscary.txt
        \Cyberpunk
    \Poems
        \doyoureadme.txt

will look something like this (where # represents a checkbutton):

SomeRootDirectory
    # foo.txt
    # bar.txt
    Stories
        Horror
            # scary.txt
            Trash
                # notscary.txt
        Cyberpunk
    Poems
        # doyoureadme.txt

Building the original dictionary from the directory structure is easy using a certain recipe I found at ActiveState (see below), but I hit a wall when I try to iterate over the nicely nested dictionary I am left with.

Answer 1

Here is a function that prints all your file names. It goes through all the keys in the dictionary, and if they map to things that are not dictionaries (in your case, the filename), we print out the name. Otherwise, we call the function on the dictionary that is mapped to.

def print_all_files(directory):

    for filename in directory.keys():
        if not isinstance(directory[filename], dict):
            print filename
        else:
            print_all_files(directory[filename])

So this code can be modified to do whatever you want, but it's just an example of how you can avoid fixing the depth through use of recursion.

The key thing to understand is that each time print_all_files gets called, it has no knowledge of how deep it is in the tree. It just looks at the files that are right there, and prints the names. If there are directores, it just runs itself on them.

Answer 2

This is a preliminary code. Go through it and tell me where you face problems.

Parents={-1:"Root"}
def add_dir(level, parent, index, k):
    print "Directory"
    print "Level=%d, Parent=%s, Index=%d, value=%s" % (level, Parents[parent], index, k)
def add_file(parent, index, k):
    print "File"
    print "Parent=%s, Index=%d, value=%s" %  (Parents[parent], index, k)
def f(level=0, parent=-1, index=0, di={}):
    for k in di:
        index +=1
        if di[k]:
            Parents[index]=k
            add_dir(level, parent, index, k)
            f(level+1, index, index, di[k])
        else:
            add_file(parent, index, k)

a={
    'SomeRootDirectory': {
        'foo.txt': None,
        'bar.txt': None,
        'Stories': {
            'Horror': {
                'scary.txt' : None,
                'Trash' : {
                    'notscary.txt' : None,
                    },
                },
            'Cyberpunk' : None
            },
        'Poems' : {
            'doyoureadme.txt' : None
        }
    }
}

f(di=a)