Senior Backend Developer (Python)

Expereo International; Katowice; On-site; PLN 50,000 - 80,000; Full time

Benefits offered by this job

Competitive compensation

Pension Plan

Hybrid Working

25 Days Holidays

Job summary

Expereo International is looking for a Backend Developer in Katowice to enhance their Supplier onboarding and Quote Management teams. You will work daily with Python and C# to build services and solve real-world challenges like optimization and partner integrations. Responsibilities include implementing business logic, designing APIs, and maintaining code quality in a mixed-language environment. The position offers competitive compensation, a pension plan, hybrid working, and opportunities for career growth.

Qualifications

• Proficient in writing clean, tested, reusable code in Python.
• Experience designing and maintaining REST APIs with clear contracts.
• Familiarity with cloud infrastructure services like AWS.

Responsibilities

• Implement and maintain business logic for quote engine.
• Define and manage API contracts, ensuring reliability.
• Refactor existing code to meet production engineering standards.

Skills

Advanced Python

API design and implementation

Software engineering discipline

Mixed-language codebase ability

Tools

C#

AWS services

API specification tooling (OpenAPI/Swagger)

Job description

About the Role

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.

The core of the role sits at the intersection of three things:

• Algorithmic implementation — translating complex commercial requirements into deterministic, auditable logic. You will implement and maintain the optimization engine that drives our quote generation.
• API design and contract maintenance — defining clear contracts between services, and ensuring the interface is clean, versioned, and reliable for downstream consumers.
• Code quality and engineering discipline — making code production-ready and scalable: writing tests, applying engineering standards, and ensuring the codebase can grow with the platform.

You will work directly with the innovation and commercial teams.

This role is also designed with growth in mind. The knowledge and context you build here — deep familiarity with the platform, the commercial logic, and the constraints of the business — make this a natural stepping stone toward a technical execution role, potentially supporting a commercial STO (single thread owner) function as the platform scales.

Key Responsibilities

Business Logic Implementation

• 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.

API Design & Contract Maintenance

• 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.

Code Quality & Engineering Practices

• 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.

Collaboration & Communication

• 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.

Must-Have

• 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.

Strong Plus

• 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

• Competitive compensation
• Pension Plan
• Hybrid Working
• 25 Days Holidays
• 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.