- Issue #15906: Fix a regression in argparse caused by the preceding change,
when action='append', type='str' and default=[].
diff --git a/Lib/argparse.py b/Lib/argparse.py
index d5976e9..66cd70a 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1961,6 +1961,7 @@
# twice (which may fail) if the argument was given, but
# only if it was defined already in the namespace
if (action.default is not None and
+ isinstance(action, _StoreAction) and
hasattr(namespace, action.dest) and
action.default is getattr(namespace, action.dest)):
setattr(namespace, action.dest,