Issue #19946: Raise ImportError when the main module cannot be found

by multiprocessing.spawn (before it was raising an AttributeError).

Lib/multiprocessing/spawn.py

@@ -248,6 +248,8 @@ def import_main_path(main_path):
         main_module = types.ModuleType(main_name)
         # XXX Use a target of main_module?
         spec = importlib.find_spec(main_name, path=dirs)
+        if spec is None:
+            raise ImportError(name=main_name)
         methods = importlib._bootstrap._SpecMethods(spec)
         methods.init_module_attrs(main_module)
         main_module.__name__ = '__mp_main__'

Misc/NEWS

@@ -44,6 +44,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #19946: multiprocessing.spawn now raises ImportError when the module to
+  be used as the main module cannot be imported.
+
 - Issue #17919: select.poll.poll() again works with poll.POLLNVAL on AIX.
 
 - Issue #19063: if a Charset's body_encoding was set to None, the email