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NIE

Número de Identidad de Extranjero (NIE)

Overview

The NIE identifies foreign residents. It resembles the DNI but starts with a prefix letter X, Y, or Z, followed by seven digits and the familiar control letter. Each prefix maps to a digit so that NIEs share the same control-letter logic as DNIs.

Algorithm Walkthrough

  1. Canonicalise by uppercasing the value; inputs must already be the correct length without separators.
  2. Format check against the regular expression [XYZ]\d{7}[A-Z].
  3. Translate the prefix to a digit using {"X": "0", "Y": "1", "Z": "2"} and concatenate it with the seven digits to create an eight-digit number.
  4. Compute the remainder of that number divided by 23.
  5. Map to the control letter using the same TRWAGMYFPDXBNJZSQVHLCKE sequence used for DNIs.
  6. Validate that the calculated letter matches the provided letter.

Worked Examples

  • X1234567L: prefix X → 0, number 01234567, remainder 11, expected letter L.
  • Y1234567X: prefix Y → 1, number 11234567, remainder 21, expected letter X.
  • Z1234567R: prefix Z → 2, number 21234567, remainder 18, expected letter R.

Formal Specification

  • Input must be exactly 9 ASCII characters.
  • Character 1: X, Y, or Z.
  • Characters 2–8: digits 0-9.
  • Character 9: uppercase letter A-Z.
  • Let prefix_map = {"X": "0", "Y": "1", "Z": "2"}.
  • Let n = int(prefix_map[char1] + chars2to8).
  • Let letters = "TRWAGMYFPDXBNJZSQVHLCKE".
  • Valid iff letters[n % 23] == character9.

Using the Library

from spanish_nif import NIE, InvalidNIE

nie = NIE("X1234567L")
assert nie.prefix == "X"
assert nie.number == 1234567  # numeric value used for the control-letter calculation

if not NIE.is_valid("x1234567l"):  # uppercased internally, so this returns True
    raise RuntimeError("Unexpected validation failure")

Generating Sample NIEs

The NIE.random() helper returns valid identifiers for fixtures and demos:

from spanish_nif import NIE

nie = NIE.random()
assert nie[0] in {"X", "Y", "Z"}
assert len(nie) == 9

For reproducible sequences, provide your own random.Random instance.

Official References