Traversing a multidimensional structure and applying strip() to all strings

Question

I'm trying to apply string.strip() to all the leafs that are strings in a multidimensional collection, but my Python is a bit rusty (to say the least). The following is the best I've come up with, but I suspect there's a much better way to do it.

def strip_spaces( item ):
    if hasattr( item, "__iter__" ):
        if isinstance( item, list ):
            return [strip_spaces( value ) for value in item]
        elif isinstance( item, dict ):
            return dict([(value,strip_spaces(value)) for value in item])
        elif isinstance( item, tuple ):
            return tuple([ strip_spaces( value ) for value in item ])
    elif isinstance( item, str ) or isinstance( item, unicode ):
        item = item.strip()
    return item

Answer 1

I don't understand why you are checking for an __iter__ attribute, as you don't seem to use it. However I would recommend a couple of changes:

• Use Abstract Base Classes in the collections module to test duck types, such as "Iterable"
• Use types.StringTypes to detect string types

.

import collections
import types

def strip_spaces( item ):
    if isinstance( item, types.StringTypes ):
        return item.strip()

    if isinstance( item, collections.Iterable ):
        if isinstance( item, list ):
            return [ strip_spaces( value ) for value in item ]

        elif isinstance( item, dict ):
            return dict([ ((strip_spaces(key), strip_spaces(value)) \
                                    for key, value in item.iteritems() ])

        elif isinstance( item, tuple ):
            return tuple( [ strip_spaces( value ) for value in item ] )

    return item

Answer 2

elif isinstance( item, dict ):
    return dict([(value,strip_spaces(value)) for value in item])

This will transform { ' a ': ' b ' } into {' a ': 'a' }, which I suspect is not what you want. How about:

    return dict([(key, strip_spaces(value)) for key, value in item.items()])