ChainMap in Practice

Introduction

Practical applications of ChainMap for organizing hierarchical data and configurations.

Configuration System

from collections import ChainMap

class Config:
    def __init__(self, defaults, environment, runtime):
        self.chain = ChainMap(runtime, environment, defaults)
    
    def get(self, key, default=None):
        return self.chain.get(key, default)
    
    def __getitem__(self, key):
        return self.chain[key]

defaults = {"db_host": "localhost", "db_port": 5432}
env = {"db_host": "prod.example.com"}
runtime = {"db_port": 5433}

config = Config(defaults, env, runtime)
print(config["db_host"])  # prod.example.com
print(config["db_port"]) # 5433

Namespace Stacking

from collections import ChainMap

builtin_vars = {"__name__": "__main__", "print": print}
global_vars = {"count": 0, "data": []}
local_vars = {"count": 5, "temp": "value"}

all_vars = ChainMap(local_vars, global_vars, builtin_vars)
print(all_vars["count"])  # 5 (local)

Practice Problems

1. Build layered configuration system
2. Implement scoped variable access
3. Create namespace with inheritance
4. Merge environment configs
5. Build template context system