isbn-pure

Pure-stdlib ISBN-13 and ISBN-10 validator for Python — zero pip dependencies, ≤150 LOC core, ≥100 tests.

from isbn_pure import validate_isbn13, validate_isbn10, normalize_isbn13, normalize_isbn10

validate_isbn13("978-0-13-468599-1")  # -> True
validate_isbn13("978-0-13-468599-0")  # -> False (wrong check digit)
validate_isbn10("0-306-40615-2")       # -> True
validate_isbn10("000000006X")          # -> True (X check digit, verified valid)
normalize_isbn13("978-0-13-468599-1") # -> "9780134685991"
normalize_isbn10("0-306-40615-2")      # -> "0306406152"

Install

pip install -e .

No external dependencies. Python ≥3.8.

Why isbn-pure?

Existing ISBN validators on PyPI require heavy runtime dependencies:

isbn-pure is zero-dependency — pure stdlib only. Ideal for serverless functions, MicroPython, Pyodide, and any environment where C extensions or network libraries are unavailable.

Key Features

• ISBN-13 validation — full ISO 2108 checksum validation
• ISBN-10 validation — full ISBN-10 checksum validation including X check digit (= 10)
• Normalization — strip hyphens/spaces, returns clean digit string
• Pure stdlib — zero pip dependencies
• ≤150 LOC core — auditable, minimal attack surface
• ≥100 tests — comprehensive valid/invalid/boundary coverage

API Reference

validate_isbn13(isbn: str) -> bool

Returns True if the string is a valid ISBN-13, False otherwise. Strips hyphens and spaces before validation.

validate_isbn10(isbn: str) -> bool

Returns True if the string is a valid ISBN-10, False otherwise. Strips hyphens and spaces. Accepts X (or x) as the check digit in position 10.

normalize_isbn13(isbn: str) -> str

Returns the 13-digit normalized ISBN string if valid, otherwise "".

normalize_isbn10(isbn: str) -> str

Returns the 10-character normalized ISBN string if valid, otherwise "".

compute_check_digit_isbn13(first12: str) -> int

Computes the ISBN-13 check digit (0–9) for a 12-digit prefix.

compute_check_digit_isbn10(first9: str) -> str

Computes the ISBN-10 check digit for a 9-digit prefix. Returns '0'–'9' or 'X'.

Canonical Test Vectors

ISBN-13:

ISBN-10:

Acceptance Criteria Checklist

• AC1: validate_isbn13("978-0-13-468599-1") returns True
• AC2: validate_isbn13("978-0-13-468599-0") returns False
• AC3: validate_isbn10("0-306-40615-2") returns True
• AC4: validate_isbn10("155404295X") returns True
• AC5: normalize_isbn13("978-0-13-468599-1") returns "9780134685991"; invalid returns ""
• AC6: Normalized ISBN re-validates: validate_isbn13(normalize_isbn13(x)) == True for all valid x
• AC7: Handles hyphens, spaces, lowercase x accepted for ISBN-10
• AC8: Pure Python stdlib only — zero pip dependencies
• AC9: Core LOC ≤ 150 (excluding tests)
• AC10: 100+ unit tests covering valid/invalid inputs, boundary cases

Run Tests

pip install -e .[dev]
pytest -v

Limitations

Format-only validation. isbn-pure validates the checksum algorithm only — it does NOT query any ISBN registry or database to verify that the ISBN corresponds to an actual published title. A structurally valid ISBN may not correspond to a real book.

Non-Goals

• ISBN-to-title lookup or registry queries
• CLI interface
• ISBN-10 to ISBN-13 conversion ( GS1 conversion)
• Integration with bibliographic databases

License

MIT