bpo-39912: Raise appropriate exceptions in filterwarnings() and simplefilter() (GH-18878)

Lib/test/test_warnings/__init__.py

@@ -375,6 +375,28 @@ class FilterTests(BaseTest):
                 "appended duplicate changed order of filters"
             )
 
+    def test_argument_validation(self):
+        with self.assertRaises(ValueError):
+            self.module.filterwarnings(action='foo')
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings('ignore', message=0)
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings('ignore', category=0)
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings('ignore', category=int)
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings('ignore', module=0)
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings('ignore', lineno=int)
+        with self.assertRaises(ValueError):
+            self.module.filterwarnings('ignore', lineno=-1)
+        with self.assertRaises(ValueError):
+            self.module.simplefilter(action='foo')
+        with self.assertRaises(TypeError):
+            self.module.simplefilter('ignore', lineno=int)
+        with self.assertRaises(ValueError):
+            self.module.simplefilter('ignore', lineno=-1)
+
     def test_catchwarnings_with_simplefilter_ignore(self):
         with original_warnings.catch_warnings(module=self.module):
             self.module.resetwarnings()

Lib/warnings.py

@@ -139,14 +139,18 @@ def filterwarnings(action, message="", category=Warning, module="", lineno=0,
     'lineno' -- an integer line number, 0 matches all warnings
     'append' -- if true, append to the list of filters
     """
-    assert action in ("error", "ignore", "always", "default", "module",
+    if action not in {"error", "ignore", "always", "default", "module", "once"}:
-                      "once"), "invalid action: %r" % (action,)
+        raise ValueError(f"invalid action: {action!r}")
-    assert isinstance(message, str), "message must be a string"
+    if not isinstance(message, str):
-    assert isinstance(category, type), "category must be a class"
+        raise TypeError("message must be a string")
-    assert issubclass(category, Warning), "category must be a Warning subclass"
+    if not isinstance(category, type) or not issubclass(category, Warning):
-    assert isinstance(module, str), "module must be a string"
+        raise TypeError("category must be a Warning subclass")
-    assert isinstance(lineno, int) and lineno >= 0, \
+    if not isinstance(module, str):
-           "lineno must be an int >= 0"
+        raise TypeError("module must be a string")
+    if not isinstance(lineno, int):
+        raise TypeError("lineno must be an int")
+    if lineno < 0:
+        raise ValueError("lineno must be an int >= 0")
 
     if message or module:
         import re
@@ -172,10 +176,12 @@ def simplefilter(action, category=Warning, lineno=0, append=False):
     'lineno' -- an integer line number, 0 matches all warnings
     'append' -- if true, append to the list of filters
     """
-    assert action in ("error", "ignore", "always", "default", "module",
+    if action not in {"error", "ignore", "always", "default", "module", "once"}:
-                      "once"), "invalid action: %r" % (action,)
+        raise ValueError(f"invalid action: {action!r}")
-    assert isinstance(lineno, int) and lineno >= 0, \
+    if not isinstance(lineno, int):
-           "lineno must be an int >= 0"
+        raise TypeError("lineno must be an int")
+    if lineno < 0:
+        raise ValueError("lineno must be an int >= 0")
     _add_filter(action, None, category, None, lineno, append=append)
 
 def _add_filter(*item, append):

Misc/NEWS.d/next/Library/2020-03-09-15-08-29.bpo-39912.xPOBBY.rst

@@ -0,0 +1,3 @@
+:func:`warnings.filterwarnings()` and :func:`warnings.simplefilter()` now raise
+appropriate exceptions instead of ``AssertionError``. Patch contributed by
+Rémi Lapeyre.