From d5c5ac5f12777182393681ddb884e53938167bce Mon Sep 17 00:00:00 2001
From: Steven Loria <sloria1@gmail.com>
Date: Tue, 23 Jul 2019 22:38:51 -0400
Subject: [PATCH] Use explicit type check instead of duck typing

See https://github.com/marshmallow-code/webargs/issues/406#issuecomment-514379744
---
 CHANGELOG.rst       | 12 ++++++++++++
 src/webargs/core.py |  6 +++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 2c9f5ca1..ade17396 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -1,6 +1,18 @@
 Changelog
 ---------
 
+5.4.0 (unreleased)
+******************
+
+Changes:
+
+* Use explicit type check for `fields.DelimitedList` when deciding to
+  parse value with `getlist()` (`#406 (comment) <https://github.com/marshmallow-code/webargs/issues/406#issuecomment-514446228>`_ ).
+
+Support:
+
+* Add "Parsing Lists in Query Strings" section to docs (:issue:`406`).
+
 5.3.2 (2019-06-19)
 ******************
 
diff --git a/src/webargs/core.py b/src/webargs/core.py
index b4b2fb37..2f4a5be7 100644
--- a/src/webargs/core.py
+++ b/src/webargs/core.py
@@ -65,7 +65,11 @@ class Meta(object):
 
 def is_multiple(field):
     """Return whether or not `field` handles repeated/multi-value arguments."""
-    return isinstance(field, ma.fields.List) and not hasattr(field, "delimiter")
+    from webargs import fields  # prevent circular import
+
+    return isinstance(field, ma.fields.List) and not isinstance(
+        field, fields.DelimitedList
+    )
 
 
 def get_mimetype(content_type):