Added workaround to still show the diff on containers with unsortable elements.

fix issue #718

AUTHORS

@@ -24,6 +24,7 @@ Daniel Grana
 Daniel Nuri
 Dave Hunt
 David Mohr
+Edison Gustavo Muenz
 Floris Bruynooghe
 Graham Horler
 Grig Gheorghiu

CHANGELOG

@@ -16,6 +16,9 @@
 - fix issue748: unittest.SkipTest reports to internal pytest unittest plugin.
   Thanks Thomas De Schampheleire for reporting and Bruno Oliveira for the PR.
 
+- fix issue718: failed to create representation of sets containing unsortable
+  elements in python 2. Thanks Edison Gustavo Muenz
+
 2.7.1 (compared to 2.7.0)
 -----------------------------
 

_pytest/assertion/util.py

@@ -225,10 +225,18 @@ def _compare_eq_iterable(left, right, verbose=False):
     # dynamic import to speedup pytest
     import difflib
 
-    left = pprint.pformat(left).splitlines()
-    right = pprint.pformat(right).splitlines()
-    explanation = [u('Full diff:')]
-    explanation.extend(line.strip() for line in difflib.ndiff(left, right))
+    try:
+        left_formatting = pprint.pformat(left).splitlines()
+        right_formatting = pprint.pformat(right).splitlines()
+        explanation = [u('Full diff:')]
+    except Exception:
+        # hack: PrettyPrinter.pformat() in python 2 fails when formatting items that can't be sorted(), ie, calling
+        # sorted() on a list would raise. See issue #718.
+        # As a workaround, the full diff is generated by using the repr() string of each item of each container.
+        left_formatting = sorted(repr(x) for x in left)
+        right_formatting = sorted(repr(x) for x in right)
+        explanation = [u('Full diff (fallback to calling repr on each item):')]
+    explanation.extend(line.strip() for line in difflib.ndiff(left_formatting, right_formatting))
     return explanation
 
 

testing/test_assertion.py

@@ -569,3 +569,39 @@ def test_AssertionError_message(testdir):
         *assert 0, (x,y)*
         *AssertionError: (1, 2)*
     """)
+
+@pytest.mark.skipif(PY3, reason='This bug does not exist on PY3')
+def test_set_with_unsortable_elements():
+    # issue #718
+    class UnsortableKey(object):
+        def __init__(self, name):
+            self.name = name
+
+        def __lt__(self, other):
+            raise RuntimeError()
+
+        def __repr__(self):
+            return 'repr({0})'.format(self.name)
+
+        def __eq__(self, other):
+            return self.name == other.name
+
+        def __hash__(self):
+            return hash(self.name)
+
+    left_set = set(UnsortableKey(str(i)) for i in range(1, 3))
+    right_set = set(UnsortableKey(str(i)) for i in range(2, 4))
+    expl = callequal(left_set, right_set, verbose=True)
+    # skip first line because it contains the "construction" of the set, which does not have a guaranteed order
+    expl = expl[1:]
+    dedent = textwrap.dedent("""
+        Extra items in the left set:
+        repr(1)
+        Extra items in the right set:
+        repr(3)
+        Full diff (fallback to calling repr on each item):
+        - repr(1)
+        repr(2)
+        + repr(3)
+    """).strip()
+    assert '\n'.join(expl) == dedent