REUSE Compliance Tool

Common errors

• Command 'reuse' not found

  cause The 'reuse' executable is not installed or is not in your system's PATH.
  fix Ensure the library is installed with `pip install reuse` and that your Python environment's script directory is included in your system's PATH.

• UnicodeDecodeError: 'utf-8' codec can't decode byte 0x... in position ...: invalid start byte

  cause The `reuse` tool attempted to read a file with an incorrect encoding, often due to misdetection by `charset-normalizer` or a genuinely malformed file.
  fix Try using the `chardet` encoding module as a workaround: `REUSE_ENCODING_MODULE=chardet reuse lint .` If the issue persists, verify the file's actual encoding and ensure it's valid UTF-8 or consider specifying an explicit encoding for the file if `reuse` offers such a parameter (which it currently does not for `lint`).

• Errors in files: [...] - reuse lint returned non-zero exit code (e.g., 1)

  cause The `reuse lint` command detected one or more files that do not comply with the REUSE specification, leading to a non-zero exit code indicating failure.
  fix Review the detailed output from `reuse lint` to identify the specific errors (e.g., missing copyright, missing license identifier, invalid SPDX expression). Correct the identified issues in your files or add appropriate `REUSE-IgnoreStart`/`REUSE-IgnoreEnd` tags.

Warnings

• breaking Starting from v6.0.0, `reuse lint` now reads entire files for REUSE information instead of just the first 4 KiB. This change can lead to new 'false positive' findings if ignored sections exist deeper in files.
  Fix: To resolve new false positives, ensure any ignored sections are explicitly marked with `REUSE-IgnoreStart` and `REUSE-IgnoreEnd` tags in the relevant files.
• gotcha In v6.1.0, a bug was identified where `charset-normalizer` (the default encoding detection module) could incorrectly detect UTF-8 files as binary if the 2048th byte was a non-final byte of a multi-byte glyph.
  Fix: As a workaround, you can force the use of `chardet` for encoding detection by setting the environment variable: `REUSE_ENCODING_MODULE=chardet reuse <command>`.
• gotcha The `reuse` library is primarily designed as a command-line interface (CLI) tool. While programmatic access via `reuse.main.main` is possible, the internal APIs are not officially stable or guaranteed to maintain compatibility across versions for direct Python imports beyond `main`.
  Fix: For scripting and automation, prefer invoking `reuse` as a subprocess (`subprocess.run(['reuse', ...])`) for maximum stability and robustness, rather than relying on direct imports of internal modules.

Install

• pip install reuse Install stable version

Imports

• main

  from reuse.main import main

  The 'reuse' library is primarily a CLI tool. The 'main' function serves as the programmatic entry point for running commands, mimicking command-line execution by taking a list of arguments.

Quickstart

This quickstart demonstrates how to use the `reuse` tool programmatically by directly calling its `main` function. It simulates command-line execution by manipulating `sys.argv` and creating a temporary project structure to run `lint` and `spdx` commands.

import sys
from pathlib import Path
from reuse.main import main

# Create a dummy project for demonstration
project_path = Path("my_reuse_project")
project_path.mkdir(exist_ok=True)

# Create a Python file with an SPDX license identifier
(project_path / "main.py").write_text("# SPDX-License-Identifier: MIT")

# Create a dummy LICENSE file
(project_path / "LICENSE").write_text("MIT License\nCopyright (c) 2024 User")

# Simulate running 'reuse lint my_reuse_project'
print("\n--- Running 'reuse lint my_reuse_project' ---")
original_argv = sys.argv
sys.argv = ['reuse', 'lint', str(project_path)]
try:
    main()
except SystemExit as e:
    # main() calls sys.exit() with 0 for success, non-zero for failure
    if e.code != 0:
        print(f"Command 'lint' failed with exit code {e.code}")
finally:
    sys.argv = original_argv # Restore original argv

# Simulate running 'reuse spdx --json my_reuse_project'
print("\n--- Running 'reuse spdx --json my_reuse_project' ---")
sys.argv = ['reuse', 'spdx', '--json', str(project_path)]
try:
    main()
except SystemExit as e:
    if e.code != 0:
        print(f"Command 'spdx' failed with exit code {e.code}")
finally:
    sys.argv = original_argv

# Clean up dummy files and directory
(project_path / "main.py").unlink()
(project_path / "LICENSE").unlink()
project_path.rmdir()