Elegant way to remove fields from nested dictionaries

Question

Hi! I had to remove some fields from a dictionary, the keys of this fields are on a list. So I write this function:

def delete_keys_from_dict(dict_del, lst_keys):
    """
    Delete the keys present in the lst_keys from the dictionary.
    Loops recursively over nested dictionaries.
    """
    dict_foo = dict_del.copy()#Used as iterator to avoid the 'DictionaryHasChanged' error
    for field in dict_foo.keys():
        if field in lst_keys:
            del dict_del[field]
        if type(dict_foo[field]) == dict:
            delete_keys_from_dict(dict_del[field], lst_keys)
    return dict_del

This code works, but it's not very elegant and I'm sure that you can code a better solution. Thaks in advance.

Answer 1

def delete_keys_from_dict(dict_del, lst_keys):
    for k in lst_keys:
        try:
            del dict_del[k]
        except KeyError:
            pass
    for v in dict_del.values():
        if isinstance(v, dict):
            delete_keys_from_dict(v, lst_keys)

    return dict_del

Answer 2

Since you already need to loop through every element in the dict, I'd stick with a single loop and just make sure to use a set for looking up the keys to delete

def delete_keys_from_dict(dict_del, the_keys):
    """
    Delete the keys present in the lst_keys from the dictionary.
    Loops recursively over nested dictionaries.
    """
    # make sure the_keys is a set to get O(1) lookups
    if type(the_keys) is not set:
        the_keys = set(the_keys)
    for k,v in dict_del.items():
        if k in the_keys:
            del dict_del[k]
        if isinstance(v, dict):
            delete_keys_from_dict(v, the_keys)
    return dict_del