Python: Nested Dictionaries vs Dictionary Plus a Dataclass

The use case involves reading user attributes like name, status, and gender given the associated user UUID. This is a write-once and read many times scenario. Also, it is assumed that all the data will fit into memory.

Nested Dictionaries

The nested dictionary creation will look something like the following:

nested_dict_approach = {  
    '19acc7df-9c8b-11eb-9022-cc2f71aeb20c' : {
        'name': 'fred',
        'status': 'active',
        'gender': 'M' 
    },
    '19acc7df-9c8b-11eb-9022-cc2f71aeb20d' : {
        'name': 'barney',
        'status': 'inactive',
        'gender': 'M' 
    },
    '19acc7df-9c8b-11eb-9022-cc2f71aeb20e' : {
        'name': 'wilma',
        'status': 'unknown',
        'gender': 'F' 
    },
}

The constant repetition of the nested key names is annoying and results in verbose and error-prone code.

To access a particular user via a UUID is straightforward.

nested_dict_approach['19acc7df-9c8b-11eb-9022-cc2f71aeb20c']

{'name': 'fred', 'status': 'active', 'gender': 'M'}

The downside of the above output is that it is just a list of attributes with no unifying principle.

To access a particular attribute of a user via a UUID is also straightforward.

nested_dict_approach['19acc7df-9c8b-11eb-9022-cc2f71aeb20c']['name']

'fred'

Dictionary Plus a Dataclass

The dictionary plus a dataclass creation will look something like the following.

from dataclasses import dataclass

@dataclass
class User:
    name: str
    status: str
    gender: str

user_1 = User('fred', 'active', 'M')
user_2 = User('barney', 'inactive', 'M')
user_3 = User('wilma', 'unknown', 'F')

dict_plus_data_class_approach = {  
    '19acc7df-9c8b-11eb-9022-cc2f71aeb20c' : user_1,
    '19acc7df-9c8b-11eb-9022-cc2f71aeb20d' : user_2,
    '19acc7df-9c8b-11eb-9022-cc2f71aeb20e' : user_3,
}

The constant repetition of the nested key names is eliminated. The other benefit is that we can specify the data types of each of the attributes.

Accessing a particular user via a UUID is the same.

dict_plus_data_class_approach['19acc7df-9c8b-11eb-9022-cc2f71aeb20c']

User(name='fred', status='active', gender='M')

However, notice that the output now is not just a list of attributes. The attributes are organized into a User.

To access a particular attribute of a user via a UUID just use a dot (".") as opposed to square brackets ("[]").

dict_plus_data_class_approach['19acc7df-9c8b-11eb-9022-cc2f71aeb20c'].name

'fred'
Summary

In summary, if you are using nested dictionaries, stop and consider using a dictionary combined with a dataclass.