PythonDictionariesAdvanced Patterns & Performance

Advanced Dictionary Patterns

Beyond the basics, dictionaries are at the heart of many advanced programming patterns in Python. Understanding these techniques will help you write more sophisticated, efficient, and robust code, especially when dealing with complex data structures, performance-critical applications, and external data sources like APIs.

Merging Dictionaries

While the | operator and .update() method are great for simple merges, real-world scenarios can be more complex.

Shallow Merge (Recap)

Standard merging (| or .update()) is shallow. It only merges the top-level keys. If a value is a nested dictionary, the entire inner dictionary from the right-hand side replaces the one on the left.

Pyground

Demonstrate how a standard merge overwrites a nested dictionary completely.

Expected Output:

{'user': {'theme': 'dark'}, 'permissions': ['read']}

Output:



Dictionaries for Caching and Memoization


A dictionary is a perfect data structure for caching—storing the results of expensive computations to avoid re-calculating them. This pattern is called memoization.


Pyground
Create a function to simulate fetching data from a slow database, using a dictionary as a cache to speed up subsequent calls.
Expected Output:

Cache miss. Querying database for user 101...
{'id': 101, 'name': 'User 101'}
Cache hit for user 101!
{'id': 101, 'name': 'User 101'}

Output:


For a more robust and automated way to cache function results, check out the @functools.lru_cache decorator in Python’s standard library.


Working with JSON


JSON (JavaScript Object Notation) is the de facto standard for data exchange on the web. The json module in Python makes it trivial to convert between Python dictionaries and JSON strings.


    

  • json.dumps(): Dumps a Python dictionary to a JSON formatted string.
    • 

  • json.loads(): Loads a JSON formatted string into a Python dictionary.
    • 



Pyground
Convert a Python dictionary to a JSON string and back.
Expected Output:

--- JSON String ---
{
  "event": "user_login",
  "success": true,
  "user_id": 123,
  "details": null
}

--- Rehydrated Python Dictionary ---
{'event': 'user_login', 'success': True, 'user_id': 123, 'details': None}
Type: <class 'dict'>

Output:


OrderedDict vs. Standard dict


Before Python 3.7, standard dictionaries did not preserve insertion order. If you needed order, you had to use collections.OrderedDict.


    

  • Standard dict (Python 3.7+): Now preserves insertion order by default. This is sufficient for most use cases.
    • 

  • collections.OrderedDict: Still useful for a few reasons:

      

    • It has a move_to_end() method to reorder items.
      • 

    • Its equality check (==) considers order, whereas a standard dict’s does not.
      • 

    • It communicates the intent that order is critical to the logic.
      • 

    

    • 



Pyground
Demonstrate the `move_to_end` method of an `OrderedDict`.
Expected Output:

Initial order: ['first', 'second', 'third']
New order: ['second', 'third', 'first']

Output:
Comprehensions & Default HandlingPractice Problems