Python 3.9: Dictionary Union Operators and Native Type Hints

# Merging two dictionaries with |
default_config = {"theme": "light", "language": "en", "notifications": True}
user_config = {"theme": "dark", "font_size": 14}

final_config = default_config | user_config
print(final_config)
# {'theme': 'dark', 'language': 'en', 'notifications': True, 'font_size': 14}

# In-place update with |=
inventory = {"apples": 5, "bananas": 3, "oranges": 8}
delivery = {"apples": 10, "kiwis": 6}

inventory |= delivery
print(inventory)
# {'apples': 10, 'bananas': 3, 'oranges': 8, 'kiwis': 6}

# Practical case: multi-layer configuration merge
env_default = {"debug": False, "port": 8000, "host": "localhost"}
env_dev = {"debug": True, "log_level": "DEBUG"}
env_local = {"port": 9000}

# Chaining merges: each layer overrides the previous one
config = env_default | env_dev | env_local
print(config)
# {'debug': True, 'port': 9000, 'host': 'localhost', 'log_level': 'DEBUG'}

# Before Python 3.9:
# from typing import List, Dict, Tuple, Optional
# def process_grades(grades: List[int]) -> Dict[str, float]:

# Python 3.9: built-in types are enough
def compute_statistics(grades: list[int]) -> dict[str, float]:
    """Compute statistics for a list of grades."""
    return {
        "average": sum(grades) / len(grades),
        "minimum": float(min(grades)),
        "maximum": float(max(grades)),
    }

def find_duplicates(items: list[str]) -> set[str]:
    """Identify items that appear more than once."""
    seen = set()
    duplicates = set()
    for item in items:
        if item in seen:
            duplicates.add(item)
        seen.add(item)
    return duplicates

def index_products(products: list[tuple[str, float]]) -> dict[str, float]:
    """Transform a list of pairs into a dictionary."""
    return {name: price for name, price in products}

# Usage
stats = compute_statistics([12, 15, 18, 9, 14])
print(stats)  # {'average': 13.6, 'minimum': 9.0, 'maximum': 18.0}

duplicates = find_duplicates(["alice", "bob", "alice", "charlie", "bob"])
print(duplicates)  # {'alice', 'bob'}

from datetime import datetime, timedelta
from zoneinfo import ZoneInfo

# Create timezone-aware datetimes
paris = ZoneInfo("Europe/Paris")
new_york = ZoneInfo("America/New_York")
tokyo = ZoneInfo("Asia/Tokyo")

meeting_paris = datetime(2024, 3, 15, 14, 0, tzinfo=paris)
print(f"Paris     : {meeting_paris.strftime('%H:%M %Z')}")
# Paris     : 14:00 CET

# Convert between time zones
meeting_ny = meeting_paris.astimezone(new_york)
meeting_tokyo = meeting_paris.astimezone(tokyo)
print(f"New York  : {meeting_ny.strftime('%H:%M %Z')}")
# New York  : 08:00 EST
print(f"Tokyo     : {meeting_tokyo.strftime('%H:%M %Z')}")
# Tokyo     : 22:00 JST

# Scheduling with timezone handling
def schedule_reminder(local_time, timezone_name, delay_hours):
    """Schedule a reminder in a given time zone."""
    now = datetime.now(tz=ZoneInfo(timezone_name))
    reminder = now + timedelta(hours=delay_hours)
    return reminder

reminder = schedule_reminder("14:00", "Europe/Paris", 2)
print(f"Reminder at: {reminder.strftime('%H:%M %Z')}")

# Cleaning up URLs
urls = [
    "https://www.example.com/api/v2/users",
    "https://www.example.com/api/v2/products",
    "https://www.example.com/api/v2/orders",
]

base = "https://www.example.com/api/v2/"
endpoints = [url.removeprefix(base) for url in urls]
print(endpoints)  # ['users', 'products', 'orders']

# Processing file names
files = ["report_2024.csv", "data_2024.csv", "archive_2024.csv.bak"]

# Remove the .csv extension
without_ext = [f.removesuffix(".csv") for f in files]
print(without_ext)
# ['report_2024', 'data_2024', 'archive_2024.csv.bak']
# Note: archive_2024.csv.bak is unchanged since it doesn't end with .csv

# Removing test prefix from method names
methods = ["test_login", "test_logout", "helper_create"]
names = [m.removeprefix("test_") for m in methods]
print(names)  # ['login', 'logout', 'helper_create']