Improve entry points and allow custom language classes via entry points (#3080)

* Remove check for overwritten factory

This needs to be handled differently – on first initialization, a new factory will be added and any subsequent initializations will trigger this warning, even if it's a new entry point that doesn't overwrite a built-in.

* Add helper to only load specific entry point

Useful for loading languages via entry points, so that they can be lazy-loaded. Otherwise, all entry point languages would have to be loaded upfront.

* Check entry points for custom languages

spacy/language.py

@@ -28,7 +28,7 @@ from .lang.punctuation import TOKENIZER_INFIXES
 from .lang.tokenizer_exceptions import TOKEN_MATCH
 from .lang.tag_map import TAG_MAP
 from .lang.lex_attrs import LEX_ATTRS, is_stop
-from .errors import Errors, Warnings, user_warning
+from .errors import Errors
 from . import util
 from . import about
 
@@ -146,9 +146,6 @@ class Language(object):
         RETURNS (Language): The newly constructed object.
         """
         user_factories = util.get_entry_points("spacy_factories")
-        for factory in user_factories.keys():
-            if factory in self.factories:
-                user_warning(Warnings.W009.format(name=factory))
         self.factories.update(user_factories)
         self._meta = dict(meta)
         self._path = None

spacy/util.py

@@ -43,6 +43,11 @@ def get_lang_class(lang):
     RETURNS (Language): Language class.
     """
     global LANGUAGES
+    # Check if an entry point is exposed for the language code
+    entry_point = get_entry_point("spacy_languages", lang)
+    if entry_point is not None:
+        LANGUAGES[lang] = entry_point
+        return entry_point
     if lang not in LANGUAGES:
         try:
             module = importlib.import_module(".lang.%s" % lang, "spacy")
@@ -230,6 +235,19 @@ def get_entry_points(key):
     return result
 
 
+def get_entry_point(key, value):
+    """Check if registered entry point is available for a given name and
+    load it. Otherwise, return None.
+
+    key (unicode): Entry point name.
+    value (unicode): Name of entry point to load.
+    RETURNS: The loaded entry point or None.
+    """
+    for entry_point in pkg_resources.iter_entry_points(key):
+        if entry_point.name == value:
+            return entry_point.load()
+
+
 def is_in_jupyter():
     """Check if user is running spaCy from a Jupyter notebook by detecting the
     IPython kernel. Mainly used for the displaCy visualizer.