Try to make command line error messages from runpy easier to understand (and…

Try to make command line error messages from runpy easier to understand (and suppress traceback cruft from the implicitly invoked runpy machinery)

Lib/runpy.py

@@ -89,6 +89,9 @@ def _get_module_details(mod_name):
 
 
 # XXX ncoghlan: Should this be documented and made public?
+# (Current thoughts: don't repeat the mistake that lead to its
+# creation when run_module() no longer met the needs of
+# mainmodule.c, but couldn't be changed because it was public)
 def _run_module_as_main(mod_name, set_argv0=True):
     """Runs the designated module in the __main__ namespace
 
@@ -96,7 +99,20 @@ def _run_module_as_main(mod_name, set_argv0=True):
            __file__
            __loader__
     """
-    loader, code, fname = _get_module_details(mod_name)
+    try:
+        loader, code, fname = _get_module_details(mod_name)
+    except ImportError as exc:
+        # Try to provide a good error message
+        # for directories, zip files and the -m switch
+        if set_argv0:
+            # For -m switch, just disply the exception
+            info = str(exc)
+        else:
+            # For directories/zipfiles, let the user
+            # know what the code was looking for
+            info = "can't find '__main__.py' in %r" % sys.argv[0]
+        msg = "%s: %s" % (sys.executable, info)
+        sys.exit(msg)
     pkg_name = mod_name.rpartition('.')[0]
     main_globals = sys.modules["__main__"].__dict__
     if set_argv0: