Fold a leading non-first-name prefix into the surname (closes #121)

docs/customize.rst

@@ -295,6 +295,33 @@ You can also pass a custom set per ``Constants`` instance::
     >>> hn2.first, hn2.last
     ('abu bakr', 'al saud')
 
+Non-First-Name Prefixes
+-----------------------
+
+``CONSTANTS.non_first_name_prefixes`` is the subset of prefixes that are *never*
+a standalone first name (``de``, ``dos``, ``ibn``, ...). When a name **starts**
+with one of these, there is no first name -- the whole thing is a surname.
+
+Example::
+
+    >>> from nameparser import HumanName
+    >>> hn = HumanName("de Mesnil")
+    >>> hn.first, hn.last
+    ('', 'de Mesnil')
+
+A member must be a prefix that is never a given name in any culture, and the set
+must stay **disjoint** from ``first_name_prefixes`` (a word cannot both join to
+the first name and never be a first name). Ambiguous particles that *can* be
+given names (``van``, ``von``, ``della``, ``di``, ``del``, ...) are intentionally
+excluded; add them yourself if your data warrants it::
+
+    >>> from nameparser.config import CONSTANTS
+    >>> CONSTANTS.non_first_name_prefixes.add('von')  # doctest: +SKIP
+
+To **disable** the feature entirely::
+
+    >>> CONSTANTS.non_first_name_prefixes.clear()  # doctest: +SKIP
+
 Parser Customization Examples
 -----------------------------
 

docs/release_log.rst

@@ -7,6 +7,7 @@ Release Log
     to 1.2.1 first (which includes a one-version compatibility shim), load and
     re-pickle under 1.2.1, then upgrade to 1.3.0.
 
+    - Add ``non_first_name_prefixes`` to ``Constants``: a leading particle that is never a first name (e.g. ``"de Mesnil"``, ``"dos Santos"``) now parses as a surname with an empty first name, instead of treating the particle as the first name (closes #121)
     - Add a first-class ``maiden`` field and ``maiden_delimiters`` to ``Constants``, so a delimiter (e.g. parenthesis) can be routed to ``maiden`` instead of ``nickname`` for alternate/maiden surnames, e.g. ``"Baker (Johnson), Jenny"`` (closes #22)
     - Fix suffix-shaped parenthesized/quoted content (e.g. ``"(Ret)"``, ``"(MBA)"``) being misclassified as a nickname instead of a suffix (closes #111)
     - Add ``suffix_acronyms_ambiguous`` to ``Constants`` for acronym suffixes that also read as given-name nicknames (e.g. ``"JD"``, ``"Ed"``), used when disambiguating parenthesized/quoted content (#111)

nameparser/config/__init__.py

@@ -36,7 +36,7 @@
     from typing_extensions import Self
 
 from nameparser.util import lc
-from nameparser.config.prefixes import PREFIXES
+from nameparser.config.prefixes import PREFIXES, NON_FIRST_NAME_PREFIXES
 from nameparser.config.first_name_prefixes import FIRST_NAME_PREFIXES
 from nameparser.config.capitalization import CAPITALIZATION_EXCEPTIONS
 from nameparser.config.conjunctions import CONJUNCTIONS
@@ -264,6 +264,11 @@ class Constants:
         :py:attr:`conjunctions`  wrapped with :py:class:`SetManager`.
     :param set first_name_prefixes:
         :py:attr:`~first_name_prefixes.FIRST_NAME_PREFIXES` wrapped with :py:class:`SetManager`.
+    :param set non_first_name_prefixes:
+        :py:attr:`~prefixes.NON_FIRST_NAME_PREFIXES` wrapped with :py:class:`SetManager`.
+        The subset of prefixes that are never a first name, so a *leading* one
+        marks the whole name as a surname. Must stay disjoint from
+        ``first_name_prefixes``.
     :type capitalization_exceptions: tuple or dict
     :param capitalization_exceptions: 
         :py:attr:`~capitalization.CAPITALIZATION_EXCEPTIONS` wrapped with :py:class:`TupleManager`.
@@ -289,6 +294,7 @@ class Constants:
     first_name_titles: SetManager
     conjunctions: SetManager
     first_name_prefixes: SetManager
+    non_first_name_prefixes: SetManager
     suffix_acronyms_ambiguous: SetManager
     capitalization_exceptions: TupleManager[str]
     regexes: RegexTupleManager
@@ -463,6 +469,7 @@ def __init__(self,
                  first_name_titles: Iterable[str] = FIRST_NAME_TITLES,
                  conjunctions: Iterable[str] = CONJUNCTIONS,
                  first_name_prefixes: Iterable[str] = FIRST_NAME_PREFIXES,
+                 non_first_name_prefixes: Iterable[str] = NON_FIRST_NAME_PREFIXES,
                  capitalization_exceptions: TupleManager[str] | Iterable[tuple[str, str]] = CAPITALIZATION_EXCEPTIONS,
                  regexes: RegexTupleManager | TupleManager[re.Pattern[str]] | Iterable[tuple[str, re.Pattern[str]]] = REGEXES,
                  patronymic_name_order: bool = False,
@@ -478,6 +485,7 @@ def __init__(self,
         self.first_name_titles = SetManager(first_name_titles)
         self.conjunctions = SetManager(conjunctions)
         self.first_name_prefixes = SetManager(first_name_prefixes)
+        self.non_first_name_prefixes = SetManager(non_first_name_prefixes)
         self.suffix_acronyms_ambiguous = SetManager(suffix_acronyms_ambiguous)
         self.capitalization_exceptions = TupleManager(capitalization_exceptions)
         self.regexes = RegexTupleManager(regexes)

nameparser/config/prefixes.py

@@ -1,3 +1,39 @@
+from nameparser.config.first_name_prefixes import FIRST_NAME_PREFIXES
+
+#: The sub-set of :py:data:`PREFIXES` that are *never* a standalone first name.
+#: A name that *starts* with one of these has no first name -- the whole thing
+#: is a surname (e.g. "de Mesnil" -> last name "de Mesnil"). Curated to exclude
+#: anything that can be a given name in some culture (`al`, `van`, `von`,
+#: `della`, `di`, `del`, `da`, `vander`, ...) and anything that is also a first
+#: name prefix (`abu`). When unsure, leave a word out: a missing member just
+#: means that name is not auto-fixed, whereas a wrong member misparses a real
+#: person. Must stay a subset of :py:data:`PREFIXES` and disjoint from
+#: :py:data:`~nameparser.config.first_name_prefixes.FIRST_NAME_PREFIXES`.
+NON_FIRST_NAME_PREFIXES = set([
+    "'t",
+    'af',
+    'auf',
+    'av',
+    'bint',
+    'de',
+    "de'",
+    'degli',
+    'dei',
+    'delle',
+    'delli',
+    'dello',
+    'dem',
+    'der',
+    'dos',
+    'het',
+    'ibn',
+    'op',
+    'ter',
+    'vd',
+    'vom',
+    'zu',
+])
+
 #: Name pieces that appear before a last name. Prefixes join to the piece
 #: that follows them to make one new piece. They can be chained together, e.g
 #: "von der" and "de la". Because they only appear in middle or last names,
@@ -7,64 +43,55 @@
 #: appear after a prefixes. So in "pennie von bergen wessels MD", "von" will
 #: join with all following name pieces until the suffix "MD", resulting in the
 #: correct parsing of the last name "von bergen wessels".
-PREFIXES = set([
-    "'t",
+#:
+#: Defined as a static union so every :py:data:`NON_FIRST_NAME_PREFIXES` member
+#: is guaranteed to also be a prefix (and still join forward), with no drift --
+#: mirroring ``TITLES = FIRST_NAME_TITLES | {...}`` in
+#: :py:mod:`nameparser.config.titles`.
+PREFIXES = NON_FIRST_NAME_PREFIXES | set([
     'aan',
     'aen',
     'abu',
-    'af',
     'al',
-    'auf',
-    'av',
     'bar',
     'bat',
     'bin',
-    'bint',
     'bon',
     'da',
     'dal',
-    'de',
-    "de'",
-    'degli',
-    'dei',
     'del',
     'dela',
     'della',
-    'delle',
-    'delli',
-    'dello',
-    'dem',
     'den',
-    'der',
     'di',
     'dí',
     'do',
-    'dos',
     'du',
     'freiherr',
     'freiherrin',
     'heer',
-    'het',
-    'ibn',
     'la',
     'le',
     'mac',
     'mc',
-    'op',
     'san',
     'santa',
     'st',
     'ste',
     'te',
-    'ter',
     'tho',
     'thoe',
     'van',
     'vande',
     'vander',
-    'vd',
     'vel',
-    'vom',
     'von',
-    'zu',
 ])
+
+# Guard the two invariants the docstring above promises, so a future edit that
+# breaks them fails at import time instead of silently drifting until a test
+# happens to catch it.
+assert NON_FIRST_NAME_PREFIXES <= PREFIXES, \
+    "NON_FIRST_NAME_PREFIXES must stay a subset of PREFIXES"
+assert not (NON_FIRST_NAME_PREFIXES & FIRST_NAME_PREFIXES), \
+    "NON_FIRST_NAME_PREFIXES must stay disjoint from FIRST_NAME_PREFIXES"

nameparser/parser.py

@@ -599,6 +599,11 @@ def is_first_name_prefix(self, piece: str) -> bool:
         """Lowercased, leading/trailing-periods-stripped version of piece is in :py:attr:`~nameparser.config.Constants.first_name_prefixes`."""
         return lc(piece) in self.C.first_name_prefixes
 
+    def is_non_first_name_prefix(self, piece: str) -> bool:
+        """Lowercased, leading/trailing-periods-stripped version of piece is in
+        :py:attr:`~nameparser.config.Constants.non_first_name_prefixes`."""
+        return lc(piece) in self.C.non_first_name_prefixes
+
     def _join_first_name_prefix(self, pieces: list[str], reserve_last: bool) -> list[str]:
         """Join a first-name prefix to its following piece.
 
@@ -821,6 +826,21 @@ def handle_turkic_patronymic_name_order(self) -> None:
                 self.first_list,
             )
 
+    def handle_non_first_name_prefix(self) -> None:
+        """
+        A leading prefix that is never a first name means the whole name is a
+        surname -- fold first (and any middle) into last. Keys on the parsed
+        first name, so a non-leading particle ("Jean de Mesnil") is untouched
+        and title/suffix are preserved. The middle_list/last_list guard leaves a
+        degenerate bare "de" as first="de" rather than inventing a surname.
+        """
+        if (len(self.first_list) == 1
+                and self.is_non_first_name_prefix(self.first_list[0])
+                and (self.middle_list or self.last_list)):
+            self.last_list = self.first_list + self.middle_list + self.last_list
+            self.first_list = []
+            self.middle_list = []
+
     def handle_middle_name_as_last(self) -> None:
         """
         When middle_name_as_last is enabled, fold middle_list into last_list
@@ -837,6 +857,7 @@ def post_process(self) -> None:
         and :py:func:`handle_capitalization`.
         """
         self.handle_firstnames()
+        self.handle_non_first_name_prefix()
         if self.C.patronymic_name_order:
             self.handle_east_slavic_patronymic_name_order()
             self.handle_turkic_patronymic_name_order()

tests/conftest.py

@@ -35,6 +35,7 @@
     "first_name_titles",
     "conjunctions",
     "first_name_prefixes",
+    "non_first_name_prefixes",
     "capitalization_exceptions",
     "regexes",
     "nickname_delimiters",