Reference library

Dictionaries & sets

Key–value maps, uniqueness, counting, grouping, and fast lookups.

6 matches

Build an OrderedDict insertion order demo in Python 3

Demonstrate how OrderedDict preserves insertion order, how updates keep position, and how re-insertion moves keys to the end.

ordereddict dictionaries insertion-order

Python

from collections import OrderedDict

def demo_ordered_dict():
    # Create an OrderedDict and insert items in a specific order
    ordered = OrderedDict()
    ordered['banana'] = 3
    ordered['apple'] = 2
    ordered['cherry'] = 5
    ordered['date'] = 1

    print("Insertion order preserved:")
    for key, value in …

13 0 Open

Dictionaries & sets easy

How to Aggregate Order Data with Sets and Dictionaries in Python

Combine sets and dictionaries to find unique products and total quantities from a list of orders in Python.

sets dictionaries data aggregation

Python

def find_unique_products(orders):
    """Return set of all products ordered across multiple orders."""
    all_products = set()
    for order in orders:
        all_products.update(order.get("items", []))
    return all_products


def product_summary(orders):
    """Build a dictionary mapping each product to its total…

13 0 Open

Dictionaries & sets easy

How to Sort Dictionary Keys Alphabetically in Python

This code returns a list of dictionary keys sorted alphabetically, using a case-insensitive comparison while preserving the original insertion order for keys that are equal.

sorting dictionary case-insensitive

Python

data = {
    "banana": 3,
    "apple": 1,
    "Cherry": 5,
    "date": 2,
    "apple": 4,
    "Fig": 6,
    "banana": 2,
}

def sort_dict_keys_alphabetically(d):
    """Return a list of keys sorted alphabetically (case-insensitive), stable for duplicates."""
    return sorted(d.keys(), key=lambda k: k.lower())

if __n…

11 0 Open

Dictionaries & sets easy

How to Sort a Python Dictionary by Value Descending

Sort dictionary items by their values in descending order and return a new dictionary.

dictionary sorting values

Python

def sort_dict_by_value_desc(d):
    return dict(sorted(d.items(), key=lambda item: item[1], reverse=True))


if __name__ == "__main__":
    sample = {"apple": 5, "banana": 2, "cherry": 8, "date": 8}
    result = sort_dict_by_value_desc(sample)
    print(result)

12 0 Open

Dictionaries & sets easy

How to Use a Frozenset as a Dict Key in Python

Demonstrates using an immutable frozenset as a hashable dictionary key, including equality and lookup with differently-ordered elements.

frozenset dictionary hashable

Python

frozen = frozenset({"a", "b", "c"})
mapping = {frozen: "set as hashable key"}
other_frozen = frozenset(["c", "b", "a"])
print(f"Are keys equal? {frozen == other_frozen}")
print(f"Lookup with different order: {mapping[other_frozen]}")
print(f"Hash matches: {hash(frozen) == hash(other_frozen)}")

13 0 Open

Dictionaries & sets medium

LRU Cache with OrderedDict in Python

Implement an LRU cache using collections.OrderedDict to track insertion order and evict the least-recently-used item when capacity is exceeded.

lru-cache ordereddict caching

Python

from collections import OrderedDict

class LRUCache:
    def __init__(self, capacity):
        self.capacity = capacity
        self.cache = OrderedDict()

    def get(self, key):
        if key not in self.cache:
            return -1
        self.cache.move_to_end(key)
        return self.cache[key]

    def put(sel…

14 0 Open

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