From ec2d8223cff2fe83119d142c3b4b365786b3182d Mon Sep 17 00:00:00 2001
From: Tim Strazny <tim.strazny@energymeteo.de>
Date: Fri, 6 Apr 2018 14:16:12 +0200
Subject: [PATCH] Fix issue #3372

---
 AUTHORS                   |  1 +
 _pytest/python_api.py     |  9 +++++----
 changelog/3372.bugfix.rst |  1 +
 testing/python/raises.py  | 18 ++++++++++++++++++
 4 files changed, 25 insertions(+), 4 deletions(-)
 create mode 100644 changelog/3372.bugfix.rst

diff --git a/AUTHORS b/AUTHORS
index ad9541423..eb3c016a5 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -188,6 +188,7 @@ Tareq Alayan
 Ted Xiao
 Thomas Grainger
 Thomas Hisch
+Tim Strazny
 Tom Dalton
 Tom Viner
 Trevor Bekolay
diff --git a/_pytest/python_api.py b/_pytest/python_api.py
index 0b30b7ac8..1d1617d72 100644
--- a/_pytest/python_api.py
+++ b/_pytest/python_api.py
@@ -584,10 +584,11 @@ def raises(expected_exception, *args, **kwargs):
 
     """
     __tracebackhide__ = True
-    for exc in filterfalse(isclass, always_iterable(expected_exception)):
-        msg = ("exceptions must be old-style classes or"
-               " derived from BaseException, not %s")
-        raise TypeError(msg % type(exc))
+    if not issubclass(expected_exception, BaseException):
+        for exc in filterfalse(isclass, always_iterable(expected_exception)):
+            msg = ("exceptions must be old-style classes or"
+                   " derived from BaseException, not %s")
+            raise TypeError(msg % type(exc))
 
     message = "DID NOT RAISE {0}".format(expected_exception)
     match_expr = None
diff --git a/changelog/3372.bugfix.rst b/changelog/3372.bugfix.rst
new file mode 100644
index 000000000..722bdab1e
--- /dev/null
+++ b/changelog/3372.bugfix.rst
@@ -0,0 +1 @@
+``pytest.raises`` now works with exception classes that look like iterables.
diff --git a/testing/python/raises.py b/testing/python/raises.py
index 156319816..053426395 100644
--- a/testing/python/raises.py
+++ b/testing/python/raises.py
@@ -1,3 +1,4 @@
+from _pytest.outcomes import Failed
 import pytest
 import sys
 
@@ -147,3 +148,20 @@ class TestRaises(object):
         with pytest.raises(ValueError):
             with pytest.raises(IndexError, match='nomatch'):
                 int('asdf')
+
+    def test_raises_exception_looks_iterable(self):
+        from six import add_metaclass
+
+        class Meta(type(object)):
+            def __getitem__(self, item):
+                return 1/0
+
+            def __len__(self):
+                return 1
+
+        @add_metaclass(Meta)
+        class ClassLooksIterableException(Exception):
+            pass
+
+        with pytest.raises(Failed, match="DID NOT RAISE <class 'raises.ClassLooksIterableException'>"):
+            pytest.raises(ClassLooksIterableException, lambda: None)