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NIF

Número de Identificación Fiscal (NIF)

Overview

The NIF is the umbrella identifier for natural persons in Spain. In practice it accepts three historical variants:

  • Standard DNIs (eight digits plus the control letter).
  • NIEs for foreign residents (prefix X/Y/Z plus seven digits and the control letter).
  • KLM cards with prefixes K, L, or M.

Algorithm Walkthrough

  1. Canonicalise by uppercasing the input; values must already include only significant characters.
  2. Reject empties – a missing identifier is invalid.
  3. Attempt NIE validation if the prefix is X, Y, or Z. The NIE logic translates the prefix and reuses the DNI control-letter rules.
  4. Attempt DNI validation for pure eight-digit numbers.
  5. Fallback to klm prefixes K, L, or M: treat the following seven digits as the numeric part, reuse the DNI control-letter mapping on that number, and verify the trailing letter.
  6. Fail if none of the previous branches succeed.

Worked Examples

  • 12345678Z: standard DNI branch, remainder 14 → letter Z.
  • X1234567L: NIE branch; control letter from numeric value 01234567.
  • K0867756N: klm branch; digits 0867756, remainder 13 → N.

Formal Specification

  • Input must be 9 ASCII characters after removing separators.
  • Valid prefixes: digits 0-9, klm KLM, or NIE XYZ.
  • Let letters = "TRWAGMYFPDXBNJZSQVHLCKE".
  • For NIE prefixes, set n = int(prefix_map[prefix] + digits), where prefix_map = {"X": "0", "Y": "1", "Z": "2"}.
  • For klm prefixes, set n = int(digits) where digits are positions 2–8.
  • For DNI-like values, set n = int(first eight digits).
  • Valid iff letters[n % 23] == final_letter.

Using the Library

from spanish_nif import NIF, InvalidNIF

nif = NIF("K0867756N")
assert nif.variant == "klm"
assert nif.letter == "N"

if not NIF.is_valid("12345678A"):
    print("Control letter mismatch")

Generating Sample NIFs

NIF.random() builds valid identifiers for tests and demos and lets you pin the variant you need:

from spanish_nif import NIF

some_nif = NIF.random()               # variant picked automatically
klm_nif = NIF.random(variant="klm")
assert klm_nif[0] in {"K", "L", "M"}

Supply a random.Random instance if you need deterministic output (for example, inside test suites).

Official References