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Dictionaries & sets

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

5 matches

Build a defaultdict histogram of categories in Python

Count occurrences of each category in a list using collections.defaultdict(int) for automatic initialization.

from collections import defaultdict

def build_category_histogram(items):
    """Count occurrences of each category in a list of items."""
    histogram = defaultdict(int)
    for item in items:
        histogram[item] += 1
    return dict(histogram)

if __name__ == "__main__":
    categories = ["fruit", "vegetable", …

11 0 Open

Dictionaries & sets medium

How to Build a TTL Cache Dict in Python

Create a dictionary subclass that automatically expires keys after a fixed time-to-live using timestamps.

dictionary cache ttl

Python

import time

class TTLDict(dict):
    def __init__(self, ttl, *args, **kwargs):
        self.ttl = ttl
        self._expires = {}
        super().__init__(*args, **kwargs)

    def __setitem__(self, key, value):
        super().__setitem__(key, value)
        self._expires[key] = time.time() + self.ttl

    def __geti…

16 0 Open

Dictionaries & sets easy

How to Set Nested Dict Value Creating Missing Keys in Python

Set a value deep inside a nested dictionary, automatically creating any missing intermediate dicts along the path.

dictionary nested mutation

Python

def set_nested_value(d, keys, value):
    """
    Set a value in a nested dict, creating missing intermediate keys.
    
    Args:
        d: The dict to modify
        keys: Iterable of keys forming the path (e.g., ['a', 'b', 'c'])
        value: The value to set at the final key
    """
    current = d
    for key i…

13 0 Open

Dictionaries & sets easy

How to Use defaultdict(set) in Python to Group Unique Values

Group key-value pairs into a dictionary of sets, automatically creating a new set for each key using defaultdict.

defaultdict sets dictionaries

Python

from collections import defaultdict

def track_groups(pairs):
    groups = defaultdict(set)
    for key, value in pairs:
        groups[key].add(value)
    return groups

if __name__ == "__main__":
    data = [
        ("fruit", "apple"),
        ("fruit", "banana"),
        ("fruit", "apple"),
        ("veg", "carrot…

15 0 Open

Dictionaries & sets easy

Parse Env Vars into Typed Dict in Python

Convert a list of environment variable names into a dictionary with automatically detected types (bool, int, float, or string), defaulting missing vars to None.

env-vars type-conversion dict

Python

import os
from typing import Any, Dict


def parse_env_vars(env_names: list[str], env: Dict[str, str] | None = None) -> Dict[str, Any]:
    """Parse a list of environment variable names into a typed dict.

    Each variable is parsed as:
    - bool: "true"/"false" (case-insensitive)
    - int: if it can be converted t…

13 0 Open

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