Python recursively replace character in keys of nested dictionary?

Question

I'm trying to create a generic function that replaces dots in keys of a nested dictionary. I have a non-generic function that goes 3 levels deep, but there must be a way to do this generic. Any help is appreciated! My code so far:

output = {'key1': {'key2': 'value2', 'key3': {'key4 with a .': 'value4', 'key5 with a .': 'value5'}}} 

def print_dict(d):
    new = {}
    for key,value in d.items():
        new[key.replace(".", "-")] = {}
        if isinstance(value, dict):
            for key2, value2 in value.items():
                new[key][key2] = {}
                if isinstance(value2, dict):
                    for key3, value3 in value2.items():
                        new[key][key2][key3.replace(".", "-")] = value3
                else:
                    new[key][key2.replace(".", "-")] = value2
        else:
            new[key] = value
    return new

print print_dict(output)

UPDATE: to answer my own question, I made a solution using json object_hooks:

import json

def remove_dots(obj):
    for key in obj.keys():
        new_key = key.replace(".","-")
        if new_key != key:
            obj[new_key] = obj[key]
            del obj[key]
    return obj

output = {'key1': {'key2': 'value2', 'key3': {'key4 with a .': 'value4', 'key5 with a .': 'value5'}}}
new_json = json.loads(json.dumps(output), object_hook=remove_dots) 

print new_json

Solution 1

Yes, there exists better way:

def print_dict(d):
    new = {}
    for k, v in d.iteritems():
        if isinstance(v, dict):
            v = print_dict(v)
        new[k.replace('.', '-')] = v
    return new

(Edit: It's recursion, more on Wikipedia.)

Solution 2

Actually all of the answers contain a mistake that may lead to wrong typing in the result.

I'd take the answer of @ngenain and improve it a bit below.

My solution will take care about the types derived from dict (OrderedDict, defaultdict, etc) and also about not only list, but set and tuple types.

I also do a simple type check in the beginning of the function for the most common types to reduce the comparisons count (may give a bit of speed in the large amounts of the data).

Works for Python 3. Replace obj.items() with obj.iteritems() for Py2.

def change_keys(obj, convert):
    """
    Recursively goes through the dictionary obj and replaces keys with the convert function.
    """
    if isinstance(obj, (str, int, float)):
        return obj
    if isinstance(obj, dict):
        new = obj.__class__()
        for k, v in obj.items():
            new[convert(k)] = change_keys(v, convert)
    elif isinstance(obj, (list, set, tuple)):
        new = obj.__class__(change_keys(v, convert) for v in obj)
    else:
        return obj
    return new

If I understand the needs right, most of users want to convert the keys to use them with mongoDB that does not allow dots in key names.

Solution 3

I used the code by @horejsek, but I adapted it to accept nested dictionaries with lists and a function that replaces the string.

I had a similar problem to solve: I wanted to replace keys in underscore lowercase convention for camel case convention and vice versa.

def change_dict_naming_convention(d, convert_function):
    """
    Convert a nested dictionary from one convention to another.
    Args:
        d (dict): dictionary (nested or not) to be converted.
        convert_function (func): function that takes the string in one convention and returns it in the other one.
    Returns:
        Dictionary with the new keys.
    """
    new = {}
    for k, v in d.iteritems():
        new_v = v
        if isinstance(v, dict):
            new_v = change_dict_naming_convention(v, convert_function)
        elif isinstance(v, list):
            new_v = list()
            for x in v:
                new_v.append(change_dict_naming_convention(x, convert_function))
        new[convert_function(k)] = new_v
    return new

Solution 4

Here's a simple recursive solution that deals with nested lists and dictionnaries.

def change_keys(obj, convert):
    """
    Recursivly goes through the dictionnary obj and replaces keys with the convert function.
    """
    if isinstance(obj, dict):
        new = {}
        for k, v in obj.iteritems():
            new[convert(k)] = change_keys(v, convert)
    elif isinstance(obj, list):
        new = []
        for v in obj:
            new.append(change_keys(v, convert))
    else:
        return obj
    return new

Solution 5

You have to remove the original key, but you can't do it in the body of the loop because it will throw RunTimeError: dictionary changed size during iteration.

To solve this, iterate through a copy of the original object, but modify the original object:

def change_keys(obj):
    new_obj = obj
    for k in new_obj:
            if hasattr(obj[k], '__getitem__'):
                    change_keys(obj[k])
            if '.' in k:
                    obj[k.replace('.', '$')] = obj[k]
                    del obj[k]

---

>>> foo = {'foo': {'bar': {'baz.121': 1}}}
>>> change_keys(foo)
>>> foo
{'foo': {'bar': {'baz$121': 1}}}

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