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Python application development

Python fundamentals, type hints, modules, virtual environments, data structures, exceptions, and application organization.

pythonvenvtypingmodulesexceptions

01Pythonic foundations

Python emphasizes readability and a large standard library. Dynamic typing keeps code concise, while type hints help editors, reviewers, and static analysis understand intended values.

pythonTyped, testable business logic

from dataclasses import dataclass

@dataclass(frozen=True)
class Item:
    name: str
    price: float


def total(items: list[Item]) -> float:
    if any(item.price < 0 for item in items):
        raise ValueError("price cannot be negative")
    return sum(item.price for item in items)

02Project environment

bashVirtual environment

python -m venv .venv
source .venv/bin/activate        # Linux/macOS
# .venv\Scripts\activate      # Windows
python -m pip install -U pip
pip install -r requirements.txt

03Application structure

Keep configuration separate from secrets.
Put reusable business logic outside route/UI functions.
Use explicit database transactions for important state changes.
Log exceptions with enough context to diagnose them, but never log passwords, tokens, or secret URLs.