Restrict pymorphy2 requirement to pymorphy2 mode (#8299)

For the Russian and Ukrainian lemmatizers, restrict the `pymorphy2`
requirement to the mode `pymorphy2` so that lookup or other lemmatizer
modes can be loaded without installing `pymorphy2`.

spacy/lang/ru/lemmatizer.py

@@ -23,12 +23,13 @@ class RussianLemmatizer(Lemmatizer):
         mode: str = "pymorphy2",
         overwrite: bool = False,
     ) -> None:
+        if mode == "pymorphy2":
             try:
                 from pymorphy2 import MorphAnalyzer
             except ImportError:
                 raise ImportError(
-                "The Russian lemmatizer requires the pymorphy2 library: "
-                'try to fix it with "pip install pymorphy2"'
+                    "The Russian lemmatizer mode 'pymorphy2' requires the "
+                    "pymorphy2 library. Install it with: pip install pymorphy2"
                 ) from None
             if RussianLemmatizer._morph is None:
                 RussianLemmatizer._morph = MorphAnalyzer()

spacy/lang/uk/lemmatizer.py

@@ -18,13 +18,14 @@ class UkrainianLemmatizer(RussianLemmatizer):
         mode: str = "pymorphy2",
         overwrite: bool = False,
     ) -> None:
+        if mode == "pymorphy2":
             try:
                 from pymorphy2 import MorphAnalyzer
             except ImportError:
                 raise ImportError(
-                "The Ukrainian lemmatizer requires the pymorphy2 library and "
-                "dictionaries: try to fix it with "
-                '"pip install pymorphy2 pymorphy2-dicts-uk"'
+                    "The Ukrainian lemmatizer mode 'pymorphy2' requires the "
+                    "pymorphy2 library and dictionaries. Install them with: "
+                    "pip install pymorphy2 pymorphy2-dicts-uk"
                 ) from None
             if UkrainianLemmatizer._morph is None:
                 UkrainianLemmatizer._morph = MorphAnalyzer(lang="uk")

spacy/tests/conftest.py

@@ -281,6 +281,13 @@ def uk_tokenizer():
     return get_lang_class("uk")().tokenizer
 
 
+@pytest.fixture
+def uk_lemmatizer():
+    pytest.importorskip("pymorphy2")
+    pytest.importorskip("pymorphy2_dicts_uk")
+    return get_lang_class("uk")().add_pipe("lemmatizer")
+
+
 @pytest.fixture(scope="session")
 def ur_tokenizer():
     return get_lang_class("ur")().tokenizer

spacy/tests/lang/uk/test_lemmatizer.py

@@ -0,0 +1,8 @@
+import pytest
+from spacy.tokens import Doc
+
+
+def test_uk_lemmatizer(uk_lemmatizer):
+    """Check that the default uk lemmatizer runs."""
+    doc = Doc(uk_lemmatizer.vocab, words=["a", "b", "c"])
+    uk_lemmatizer(doc)