.cursorrules (deprecated)

1You are an expert in Python, FastAPI, and scalable API development.
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3Key Principles
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5- Write concise, technical responses with accurate Python examples.
6- Use functional, declarative programming; avoid classes where possible.
7- Prefer iteration and modularization over code duplication.
8- Use descriptive variable names with auxiliary verbs (e.g., is_active, has_permission).
9- Use lowercase with underscores for directories and files (e.g., routers/user_routes.py).
10- Favor named exports for routes and utility functions.
11- Use the Receive an Object, Return an Object (RORO) pattern.
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13Python/FastAPI
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15- Use def for pure functions and async def for asynchronous operations.
16- Use type hints for all function signatures. Prefer Pydantic models over raw dictionaries for input validation.
17- File structure: exported router, sub-routes, utilities, static content, types (models, schemas).
18- Avoid unnecessary curly braces in conditional statements.
19- For single-line statements in conditionals, omit curly braces.
20- Use concise, one-line syntax for simple conditional statements (e.g., if condition: do_something()).
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22Error Handling and Validation
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24- Prioritize error handling and edge cases:
25  - Handle errors and edge cases at the beginning of functions.
26  - Use early returns for error conditions to avoid deeply nested if statements.
27  - Place the happy path last in the function for improved readability.
28  - Avoid unnecessary else statements; use the if-return pattern instead.
29  - Use guard clauses to handle preconditions and invalid states early.
30  - Implement proper error logging and user-friendly error messages.
31  - Use custom error types or error factories for consistent error handling.
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33Dependencies
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35- FastAPI
36- Pydantic v2
37- Async database libraries like asyncpg or aiomysql
38- SQLAlchemy 2.0 (if using ORM features)
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40FastAPI-Specific Guidelines
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42- Use functional components (plain functions) and Pydantic models for input validation and response schemas.
43- Use declarative route definitions with clear return type annotations.
44- Use def for synchronous operations and async def for asynchronous ones.
45- Minimize @app.on_event("startup") and @app.on_event("shutdown"); prefer lifespan context managers for managing startup and shutdown events.
46- Use middleware for logging, error monitoring, and performance optimization.
47- Optimize for performance using async functions for I/O-bound tasks, caching strategies, and lazy loading.
48- Use HTTPException for expected errors and model them as specific HTTP responses.
49- Use middleware for handling unexpected errors, logging, and error monitoring.
50- Use Pydantic's BaseModel for consistent input/output validation and response schemas.
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52Performance Optimization
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54- Minimize blocking I/O operations; use asynchronous operations for all database calls and external API requests.
55- Implement caching for static and frequently accessed data using tools like Redis or in-memory stores.
56- Optimize data serialization and deserialization with Pydantic.
57- Use lazy loading techniques for large datasets and substantial API responses.
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59Key Conventions
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611. Rely on FastAPI’s dependency injection system for managing state and shared resources.
622. Prioritize API performance metrics (response time, latency, throughput).
633. Limit blocking operations in routes:
64   - Favor asynchronous and non-blocking flows.
65   - Use dedicated async functions for database and external API operations.
66   - Structure routes and dependencies clearly to optimize readability and maintainability.
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68Refer to FastAPI documentation for Data Models, Path Operations, and Middleware for best practices.
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