How to manipulate nested dictionaries with dotty

Table of Contents

Motivation

Sometimes a task which should be easy can be hard to accomplish in practice.

Manipulating nested dictionaries in Python seems to be such a task.

Without dotty

Accessing nested dictionaries looks like this:

data = { 
    'a': { 
        'b': { 
            'c': 'd' 
         } 
     } 
} 
assert data['a']['b']['c'] == 'd'

You have to chain the keys to get down to the nested dict and get the value for that key

With dotty

Installation

You can install dotty with

pip install dotty-dict

Usage

from dotty_dict import dotty 
data = {
    'a': {
        'b': {
            'c': 'd'
        }
    }
}

dot = dotty(data)
assert 'a.b' in dot
assert dot['a.b.c'] == 'd'

After importing dotty you can wrap your existing vanilla Python dictionary in a dotty object.

Now you can access your nested values by chaining the key with the dot to a “key path”

Updating dictionaries

data = {
    'a': {
        'b': {
            'c': 'd'
        }
    }
}
dot = dotty(data)
dot['a.b.c'] = 'e'
assert dot['a.b.c'] == {'c': 'e'}

Finding the key

If you already know the “path” to the nested dictionary you will be fine.

But if you just know the most inner key you can use this little recursive function to extract the full path to the nested dictionary:


def _get_key_path(data, key, path=None):
    found = False
    if path is None:
        path = []
    for k, v in data.items():
        if k == key:
            path.append(key)
            found = True
            break
        elif isinstance(v, dict):
            path.append(k)
            _path, found = _get_key_path(v, key, path)
            if not found:
                path.pop()
    return path, found


def get_key_path(data, key):
    key_path, _ = _get_key_path(data, key)
    key_path = ".".join(key_path)
    return key_path