Python Code
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Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
How to Build an Anti-Corruption Layer in Python
Wrap a legacy system with a translation layer that converts awkward legacy data into a clean, modern DTO (Data Transfer Object) for use by new code.
class LegacyOrderSystem:
"""Legacy system with awkward, unstructured data."""
def get_order(self):
return {
"order_id": "ORD-123",
"cust": "Acme Corp",
"items": [{"sku": "A1", "qty": 2, "price_each": 10.0}],
"ship_to": "123 Main St, Springfield"
}…How to Migrate a Legacy Facade with the Strangler Fig Pattern in Python
Use a facade to wrap a legacy API and incrementally migrate callers to a modern interface, following the strangler fig pattern.
class LegacyAPI:
"""Simulates the legacy system's raw interface."""
def get_user(self, user_id):
return {"id": user_id, "name": "Alice", "legacy": True}
class UserService:
"""Facade that wraps the legacy system with a modern interface."""
def __init__(self, legacy_api=None):
self.lega…Strangler Fig Migration Pattern in Python
Gradually reroute calls from a legacy service to a modern replacement using a runtime switch and feature detection.
from dataclasses import dataclass
@dataclass
class PaymentService:
def process(self, amount: float) -> str:
return f"Legacy processed ${amount:.2f}"
class StranglerFig:
def __init__(self):
self._new_service = None
def attach_new(self, service):
self._new_service = service
de…How to Expand a Contract and Migrate Data in Python
Expand an old data contract by renaming fields and adding defaults, then migrate to a final version with deepcopy isolation.
import json
from copy import deepcopy
# Mock data representing a user record (old contract)
old_contract = {
"id": 1,
"name": "Alice",
"email": "alice@example.com",
"age": 30,
"status": "active"
}
# Expanded contract: adds fields with defaults and renames some fields
expand_rules = {
"id": "u…How to simulate a database migration init container mock in Python
A mock init container that runs environment checks and a staged database migration job before the main application starts, printing progress to stdout.
```python
class MigrationJob:
def __init__(self, name, steps):
self.name = name
self.steps = steps
self.current_step = 0
self.status = "pending"
def run(self):
print(f"Initializing migration job: {self.name}")
for step in self.steps:
self.current_ste…Zero Downtime Migration with Dual Write Pattern in Python
Implement a dual-write pattern that writes user data to both legacy and new systems simultaneously to enable zero-downtime migration.
from datetime import datetime
import json
class UserService:
def __init__(self):
self.legacy_db = {}
self.new_db = {}
self.migration_log = []
def write_user(self, user_id, name, email):
# Write to new system first
user_record = {
"id": user_id,
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