di-container — Tape Drive CLI

A minimal Python CLI application demonstrating object-oriented design, dependency injection, and TDD with a real and simulated tape drive backend.

Features

• Clean ITapeDrive interface with two interchangeable implementations
• Dependency injection via a lightweight Container class
• Switch between the real hardware driver and the in-memory simulator with a single flag
• JSON-configurable logging (console + rotating file)
• Full pytest suite — atomic unit tests (mocked) and integration tests (simulator)

Project Structure

di-container/
├── main.py                              # CLI entry point
├── logging_config.json                  # Logging configuration
├── requirements.txt
├── pytest.ini
└── src/
    ├── interfaces/
    │   └── i_tape_drive.py              # ITapeDrive abstract interface
    ├── tape_drive.py                    # Real hardware driver (Linux mt/dev)
    ├── tape_drive_simulator.py          # In-memory simulator
    ├── tape_drive_service.py            # Service layer (receives ITapeDrive via DI)
    ├── container.py                     # DI container — wires the object graph
    └── logging_setup.py                 # Loads logging config from JSON

Installation

python -m venv .venv
# Windows
.venv\Scripts\activate
# Linux / macOS
source .venv/bin/activate

pip install -r requirements.txt

Usage

All commands accept --driver real|simulator (default: simulator) and an optional --log-config path.

Mount and inspect a tape

python main.py load TAPE-001
python main.py status

OK — tape loaded.
  driver   : simulator
  tape_id  : TAPE-001
  loaded   : True
  position : 0
  capacity : 10485760

Write and read back data

python main.py load TAPE-001
python main.py write "Hello, tape!"
python main.py rewind
python main.py read 12

OK — tape loaded.
OK — wrote 12 byte(s).
OK — tape rewound.
Read 12 byte(s): b'Hello, tape!'

Seek to a position

python main.py load TAPE-001
python main.py seek 1024
python main.py write "offset data"
python main.py seek 1024
python main.py read 11

Eject the tape

python main.py unload

Switch to the real hardware driver (Linux only)

python main.py --driver real status

The real driver communicates with /dev/nst0 via the mt utility (mt-st package).
It requires a Linux system with a connected tape device.

Use a custom logging configuration

python main.py --log-config /etc/tapedrive/logging.json status

Running Tests

# All tests
pytest

# Unit tests only (all dependencies mocked)
pytest tests/unit/

# Integration tests only (real simulator, no mocks)
pytest tests/integration/

# With coverage report
pytest --cov=src --cov-report=term-missing

tests/unit/test_tape_drive_service.py          28 passed
tests/integration/test_tape_drive_simulator.py 41 passed

Logging

Logging is configured via logging_config.json using the standard Python logging.config.dictConfig schema.

• Console — INFO and above, simple format
• File (tape_drive.log) — DEBUG and above, timestamped detailed format

Edit logging_config.json to change levels, add handlers, or switch formatters without touching the code.

{
    "loggers": {
        "tape_drive": {
            "level": "DEBUG",
            "handlers": ["console", "file"]
        }
    }
}

Design

Concept	Implementation
Interface	ITapeDrive — Python ABC with @abstractmethod
Real driver	TapeDrive — delegates to mt and /dev/nst0
Simulator	TapeDriveSimulator — bytearray in memory
Service layer	TapeDriveService — business logic, no I/O
DI container	Container — constructs and wires the graph
Logging config	LoggingSetup — loads from JSON, falls back to basicConfig