Senior Python Full-Stack Developer (PythonReact)

Project Description: We have an ambitious goal to migrate a legacy system written in HLASM (High-Level Assembler) from the mainframe to a cloud-based Java environment for one of the largest banks in the USA. Responsibilities: We are looking for an experienced Senior Python Developer who can help perform the migration of the client platform: • Troubleshoot, debug, and resolve issues in GenAI-powered code translation pipelines • Collaborate with dev and client teams to ensure alignment with project goals and deliver high-quality solutions • Maintain and fine-tune RAG application that supports the migration process, specifically optimizing LLM prompts for pattern recognition • Build and maintain FastAPI-based microservices that orchestrate the migration workflow • Implement RAG (Retrieval Augmented Generation) systems using LangChain /Langgraph/LlamaIndex for contextual code understanding • Design stateful migration workflows using LangGraph/LangChain/LlamaIndex for complex multi-step transformations • Mandatory work from the office 5 days per week Mandatory Skills Description: • Experience in front-end development (preferably React) for building migration dashboards and progress monitoring interfaces (2 years) • Proficiency in Python development (5 years), with specific expertise in: • FastAPI for building high-performance REST APIs and WebSocket connections • Async programming patterns for handling concurrent migration tasks • Pydantic for robust data validation in migration pipelines • Experience with vector embeddings and embedding models • Vector database implementation for semantic search • Graph database experience for code dependency mapping • Building agents for code analysis, implementing custom tools for mainframe-specific transformations, creating chains for multi-step code migration • Orchestrating stateful workflows for complex migration scenarios, managing checkpoints for long-running migrations, implementing conditional routing based on code patterns • Building knowledge bases from documentation, implementing hybrid search for code pattern matching, creating custom retrievers for language specific contexts • Implementing similarity search and semantic code retrieval systems Graph traversal algorithms for dependency analysis • Strong problem-solving and debugging skills for identifying translation anomalies and semantic preservation issues • Excellent communication skills for collaboration with client teams and explaining complex technical translations Nice-to-Have Skills Description: • Deep understanding of HLASM instruction sets, macro definitions, and DSECT mappings • COBOL and PL/I for understanding integrated mainframe systems • Assembly language debugging and performance optimization • Mainframe utilities (DFSORT, IEBGENER, IDCAMS) • Experience with mainframe subsystems: CICS transactions, DB2 stored procedures, JCL batch processing • Knowledge of z/OS internals, linkage conventions, and program calling standards • Familiarity with EBCDIC to ASCII conversion, packed decimal (COMP-3) handling • Experience in Java development, particularly Spring Boot, to understand target architecture requirements • Familiarity with large-scale system migrations and modernization efforts, including phased migration strategies and dual-run validation • Prior experience working in the banking or financial services industry, understanding core banking concepts, regulatory requirements, and transaction processing • Knowledge of performance tuning and optimization in cloud environments, including auto-scaling strategies and cost optimization Languages: English: B2 Upper Intermediate

Location: Madrid, Community of Madrid, ES

Posted Date: 10/24/2025