Raise a better error

python-attrs · Apr 4, 2023 · 880644e · 880644e
1 parent 898764e
commit 880644e
Show file tree

Hide file tree

Showing 2 changed files with 14 additions and 1 deletion.
diff --git a/src/attr/_funcs.py b/src/attr/_funcs.py
@@ -376,13 +376,19 @@ def evolve(*args, **changes):
     if args:
         (inst,) = args
     else:
+        try:
+            inst = changes.pop("inst")
+        except KeyError:
+            raise TypeError(
+                "evolve() missing 1 required positional argument: 'inst'"
+            )
+
         warnings.warn(
             "Passing the instance per keyword argument is deprecated and "
             "will stop working in, or after, April 2024.",
             DeprecationWarning,
             stacklevel=2,
         )
-        inst = changes.pop("inst")
 
     cls = inst.__class__
     attrs = fields(cls)

diff --git a/tests/test_funcs.py b/tests/test_funcs.py
@@ -722,3 +722,10 @@ class C:
             evolve(inst=C())
 
         assert __file__ == wi.list[0].filename
+
+    def test_no_inst(self):
+        """
+        Missing inst argument raises a TypeError like Python would.
+        """
+        with pytest.raises(TypeError, match=r"evolve\(\) missing 1"):
+            evolve(x=1)