Python Payment Module — High-Quality Implementation

A modular, production-ready payment module showcasing clean architecture, strong typing, and robust integrations with multiple payment providers (Authorize.Net, Paysafe, Jupiter, etc.). It exposes FastAPI routers backed by gRPC services and a well-structured SQLAlchemy data layer.

Highlights that demonstrate expertise

• Layered, modular architecture with clear boundaries:
  • Routers (routers/) for HTTP endpoints decoupled from business logic via gRPC stubs
  • Actions (actions/) for external provider integrations (e.g., Authorize.Net)
  • Voter (voter/) for fine-grained, user-centric authorization decisions
  • Enumerations (enumerations/) for type-safe provider and status constants
  • Domain models (models/) and validation schemas (sql/schemas/) for data integrity
  • SQL layer (sql/) split into models, crud, schemas, and database for persistence
  • Protobuf-first contracts (proto/) defining stable, language-agnostic APIs
• Strong typing and validation:
  • Pydantic models for request validation and response shaping
  • Marshmallow SQLAlchemy schemas for serialization of ORM entities
  • typing and t.Literal used in routers for compile-time validated query params
  • Enum-driven design for payment types and statuses to prevent invalid states
• Robust security and authorization:
  • JWT-based auth dependency (JWTBearer) applied consistently in routers
  • RequestHeaderValidatorInterceptor + voter classes enforcing ownership-based access
• Resilient error handling and clean responses:
  • gRPC exceptions captured and mapped to HTTPException with sanitized messages
  • Provider adapters return structured results and handle null/invalid responses gracefully
• Scalable, reliable database practices:
  • SQLAlchemy engine with connection pooling and pool_pre_ping
  • Explicit isolation level and scoped_session for thread safety
  • CRUD layer encapsulates queries with filtering, pagination, safe dynamic ordering
• Extensibility by design:
  • New payment providers are a matter of extending enums and action adapters
  • Proto/gRPC services make inter-service contracts explicit and testable
• Maintainability and readability:
  • Comprehensive docstrings, consistent naming, and clear module responsibilities
  • Consistent camelCase↔snake_case transformations for API/DB boundary handling

Tech stack

• FastAPI (routers), gRPC + Protobuf (service boundary), SQLAlchemy (ORM)
• Pydantic, Marshmallow (validation/serialization)
• Authorize.Net SDK, Requests (provider adapters)
• python-decouple (12-factor env config)

Key directories

• actions/ — Provider adapters (e.g., authnet.py)
• routers/ — HTTP route handlers for Users, Transactions, Webhooks, etc.
• voter/ — Authorization voters (ownership checks, action gating)
• enumerations/ — Enums for payment types and statuses
• models/ — Domain DTOs for API boundary
• sql/ — Persistence layer
  • database.py — engine/session config
  • models/ — ORM entities
  • crud/ — query functions and repositories
  • schemas/ — serialization schemas
• proto/ — Protobuf definitions for transactions and related entities

Notable implementation details

• Provider integration (Authorize.Net):
  • Encapsulated in AuthnetService with environment-based configuration (LIVE/TEST)
  • Clear, testable methods (e.g., CreateCustomerProfile, ChargeCreditCard) returning structured dicts
• gRPC-first API routers:
  • Routers call gRPC stubs; errors are normalized; responses are converted via MessageToDict and cased consistently
• Authorization voter pattern:
  • TransactionVoter enforces add/edit/view permissions based on the authenticated user
• Transaction querying:
  • Rich filtering and sorting; pagination metadata; safe getattr-based ordering controlled via whitelisted keys

Example surfaces

• User endpoints: /user with create/update/timezone/password routes
• Transaction endpoints: /transaction with checkout, profile payment, read, refund, list, settlement, partial refund
• gRPC TransactionService methods: CheckoutPayment, ProfilePayment, ReadTransaction, RefundTransaction, ReadRefund, CancelRefund, ReadRefundByTransactionId, ListTransactions, ReadSettlementByTransactionId, PartiallyRefundInvoiceItems

Configuration

Configure via environment variables (12-factor):

• Database: DB_ENGINE, MYSQL_USER, MYSQL_PASSWORD, MYSQL_URL, MYSQL_PORT, MYSQL_DB
• Authorize.Net: AUTH_ENVIRONMENT, AUTH_TEST_*, AUTH_LIVE_*
• Auth/JWT and gRPC channel settings via the helper layer

Run (overview)

• Ensure Python 3.10+ and dependencies installed
• Provide environment variables for DB and providers
• Start your gRPC backends referenced by the routers
• Serve the FastAPI application that mounts the routers in this module

Why this codebase stands out

• Clean separation of concerns and contracts (Routers ⇄ gRPC ⇄ DB/Providers)
• Strong typing, enums, and validation minimize runtime errors
• Security and authorization are first-class, not bolted on
• Extensible architecture makes adding providers and endpoints straightforward
• Production-minded DB setup and defensive error handling