Sazonova

Sazonova Zoriana Contact
Phone: [open contact info](look above in the "contact info" section)
Strong Junior Python Backend Developer
Email: [open contact info](look above in the "contact info" section)
Remote | Full-time | Open to international Location: Kyiv, Ukraine
opportunities

Education
Lviv Polytechnic National University | 2023–2027
B.Sc. in Computer Science

Tech Stack
• Languages: Python, SQL, Go
• Backend: FastAPI, Django/DRF, SQLAlchemy, Pydantic, Alembic
• Databases & Cache: PostgreSQL, Redis, MySQL, MongoDB
• Architecture: DDD, Clean Architecture, CQRS, Repository, Unit of Work, Service Layer
• Async & Messaging: Celery, Kafka, RabbitMQ, WebSockets
• DevOps: Docker, Docker Compose, Linux, Nginx, Git, CI/CD
• API & Security: REST API, JWT, OAuth2, Stripe/Webhooks
• Testing: pytest, async testing

Work Experience
Backend Developer | Freelance & Project-Based Development
2024–Present

Backend Developer — Booking Platform | Freelance Project | 2025
• Owned backend development for the availability, booking lifecycle, pricing, and reservation data-access modules using
Python, FastAPI, SQLAlchemy, PostgreSQL, Redis, and Celery.
• Implemented booking availability and interval-overlap logic with 30–60 min configurable buffer times, handling
boundary cases, adjacent reservations, time zones, and DST transitions.
• Optimized availability queries in PostgreSQL using range-based filtering and GiST / tstzrange indexing, reducing
unnecessary scans during slot searches.
• Developed a 5-state booking lifecycle (pending, confirmed, cancelled, completed, expired) with validation for allowed
transitions and idempotent create/approve/cancel operations.
• Built 10+ REST API endpoints for booking creation, retrieval, listing, updates, approval, cancellation, and status
handling.
• Implemented Celery + Redis background workflows for notifications, slot release after cancellation, retries, and
automatic expiration of pending reservations.
• Developed a configurable pricing engine covering seasonal multipliers, percentage/fixed discounts, and platform
commissions, using Python Decimal for monetary calculations.
• Implemented repository and selector layers for 4 core entities (Booking, Availability, Price, User), keeping SQLAlchemy
queries outside API handlers and supporting filtering, pagination, and date-range queries.
• Added Redis caching for availability searches with TTL-based expiration and cache invalidation on booking
create/update/cancel operations.
• Wrote 50+ unit and API tests across availability and pricing logic, including overlap boundaries, buffer-time conflicts,
rounding, discounts, invalid transitions, and duplicate requests.
• Configured the local development environment with Docker Compose for backend, PostgreSQL, and Redis, and handled
service dependencies, environment configuration, health checks, and container debugging.
• Collaborated with another developer on integration and code review while independently owning assigned backend
modules and business logic.
Backend Developer — Marketplace Platform | Freelance Project | 2025
Team of 2 Backend Developers
• Developed and extended backend modules for catalog, products, attributes, shopping cart, orders, discounts, coupons,
pricing, and inventory.
• Collaborated with another backend developer on implementing new features, fixing bugs, and improving existing
business logic.
• Implemented business logic for cart updates, checkout, order creation, stock validation, discounts, and coupon
application.
• Followed existing DDD and Clean Architecture principles, maintaining clear separation between API, service, domain,
and persistence layers.
• Implemented Repository and Unit of Work patterns for database access and transaction management.
• Applied CQRS-style separation between read and write operations, moving business logic and complex queries out of
FastAPI handlers.
• Built reusable pricing logic covering base prices, discounts, coupons, and final order totals.
• Implemented inventory validation and stock reservation logic to prevent checkout with insufficient quantities.
• Integrated a Stripe-like payment flow with payment intents and webhook handling for asynchronous payment status
updates.
• Added idempotency protection for repeated payment and order requests.
• Worked with a fully asynchronous backend using FastAPI, async SQLAlchemy, PostgreSQL, Redis, and Pydantic.
• Refactored duplicated service and persistence logic into reusable components, improving maintainability and
testability.
• Added tests for edge cases including invalid coupons, insufficient stock, duplicate payment events, and invalid order
state transitions.

Freelance Backend Developer — Educational Platform | 2025–2026
• Developed core backend functionality for an educational platform using Python, FastAPI, PostgreSQL, Redis, and Celery,
focusing on API design, business logic, and asynchronous processing.
• Implemented the backend pipeline for processing educational content and integrated LLM-based generation of study
notes, flashcards, quizzes, and knowledge graphs.
• Designed and implemented asynchronous workflows with Celery + Redis for long-running LLM tasks, retries, status
tracking, and background content generation.
• Built and maintained REST APIs for users, learning materials, generated content, quizzes, progress tracking, and
role-based access control.
• Implemented service, selector, and repository layers to keep business logic, database access, and API handlers
separated, and refactored existing code to reduce coupling and duplication.
• Developed data models and PostgreSQL queries for storing generated learning content, user progress, quiz results, and
relationships used in the knowledge graph.
• Implemented validation and error handling for failed LLM requests, invalid generated data, duplicate operations, and
incomplete processing states.
• Added Redis caching for frequently accessed data and implemented cache invalidation where data changed after
background processing.
• Improved reliability of asynchronous workflows through retry mechanisms, task-state handling, idempotent operations,
and structured logging.
• Wrote unit and API tests for core backend and LLM workflows, including content generation, permissions, validation,
and failure scenarios.
• Collaborated with another developer on feature planning, code integration, debugging, and backend improvements,
while independently owning assigned backend modules and tasks.

Languages
• Ukrainian — Native
• English — Upper-Intermediate (B2)