Use is_number_token instead of assertion (#3069)

Author: MarcoGorelli

src/black/__init__.py

@@ -40,7 +40,7 @@
 from black.const import DEFAULT_LINE_LENGTH, DEFAULT_INCLUDES, DEFAULT_EXCLUDES
 from black.const import STDIN_PLACEHOLDER
 from black.nodes import STARS, syms, is_simple_decorator_expression
-from black.nodes import is_string_token
+from black.nodes import is_string_token, is_number_token
 from black.lines import Line, EmptyLineTracker
 from black.linegen import transform_line, LineGenerator, LN
 from black.comments import normalize_fmt_off
@@ -1245,8 +1245,7 @@ def get_features_used(  # noqa: C901
             if value_head in {'f"', 'F"', "f'", "F'", "rf", "fr", "RF", "FR"}:
                 features.add(Feature.F_STRINGS)
 
-        elif n.type == token.NUMBER:
-            assert isinstance(n, Leaf)
+        elif is_number_token(n):
             if "_" in n.value:
                 features.add(Feature.NUMERIC_UNDERSCORES)
 

src/black/nodes.py

@@ -854,3 +854,7 @@ def is_rpar_token(nl: NL) -> TypeGuard[Leaf]:
 
 def is_string_token(nl: NL) -> TypeGuard[Leaf]:
     return nl.type == token.STRING
+
+
+def is_number_token(nl: NL) -> TypeGuard[Leaf]:
+    return nl.type == token.NUMBER