Hybrid Senior Backend Developer, Python

at Expereo

• Job title: Senior Backend Developer, Python
• Job type: Full Time
• Experience level: Senior
• Salary: Not specified
• Degree requirement: Bachelor's Degree
• Tech skills: AWS, Cloud, Python, .NET
• Location requirements: Hybrid, Katowice, Poland

About the role

• Backend Developer focusing on Python/C# services for quote management in a leading internet connectivity provider. Involved in algorithm implementation, API design, and cross-functional collaboration.

Responsibilities

• We are looking for a Backend Developer to join the Supplier onboarding and Quote Management teams and work directly on the computational core of our platform.
• You will write Python and/or dotnet every day. You will work on an existing Python/C# backend and create new services.
• You will work on solving real-world business problems, like creating a constraint optimization engine, working on integrations with our partners and creating and maintaining internal tools.
• Implement and maintain business logic for the quote engine, partner integrations and internal services: supplier selection, service bundling, routing rules, product validation …
• Explore, document and integrate heterogeneous external data sources necessary to the execution of business logic.
• Ensure all outputs are auditable, and explainable to commercial stakeholders — we don’t build black boxes.
• Validate model outputs against historical data; measure and report on prediction reliability.
• Optimize the operational value of the integrations with our partners.
• Define contracts, manage versioning, and ensure downstream consumers are never broken silently.
• Write clear, well-documented API interfaces with explicit input/output contracts and error handling.
• Coordinate with the Platform engineer on service integration and ensure clean separation of concerns between components.
• Maintain API documentation as a living artifact, not an afterthought.
• Refactor and clean up existing Python/C# code: reduce complexity, increase testability, and bring the codebase up to production engineering standards.
• Write unit and integration tests that provide real confidence — not just coverage numbers.
• Apply Git, code review, and CI practices to all work. Code lives in a repository, goes through review, and is reproducible without intervention.
• Document non-obvious logic thoroughly so knowledge is transferable.
• Partner with the Commercial teams, Quote Engine lead Platform engineer — this is collaborative work, not ticket execution.
• Participate in sprint reviews, propose approaches, and flag risks early.

Requirements

• Advanced Python — non-negotiable. Clean, tested, reusable code. Not just scripts that happen to work.
• API design and implementation. Designing and maintaining REST APIs with clear contracts, versioning, and proper error handling.
• Software engineering discipline. Testing, code review, Git, and the habits of someone who builds things that others can maintain.
• Ability to work in a mixed-language codebase. The existing platform is Python/C#. You need to be comfortable reading it and understanding the integration points.
• C#: You will also work with the existing platform, you need to write quality, clean, testable code in C#.
• Familiarity with AWS services (Lambda, API Gateway, S3) or equivalent cloud infrastructure.
• Experience with API specification tooling (OpenAPI/Swagger, Pydantic, etc.).
• Exposure to Python packaging, dependency management, and CI pipelines.
• Familiarity with constraint-solving tools such as OR-Tools, PuLP, or equivalent in a real-world setting.
• Experience in a B2B SaaS, telecom, or logistics context where algorithmic correctness has real commercial stakes.
• Comfort with performance profiling and optimization in Python.

Benefits

• Part of a team that is engaged and owning the things they do, highly trustable with direct commercial stakes.
• Direct access to production systems, real data, and decision-makers — no layers of process between your work and its impact.
• Exposure to cutting-edge technologies and large-scale global networks.
• A role designed with trajectory in mind — the knowledge you build here is directly applicable to a senior technical execution path.
• Competitive compensation
• Pension Plan
• Hybrid Working
• 25 Days Holidays