From 8c7eb8236348c8fb8db43a6a9c02ba442a09f6b8 Mon Sep 17 00:00:00 2001
From: Daniel Hahler <git@thequod.de>
Date: Wed, 15 May 2019 12:03:00 +0200
Subject: [PATCH] Fix/improve comparison of byte strings

Fixes https://github.com/pytest-dev/pytest/issues/5260.
---
 changelog/5260.bugfix.rst     |  1 +
 src/_pytest/assertion/util.py |  5 ++++-
 testing/test_assertion.py     | 12 ++++++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 changelog/5260.bugfix.rst

diff --git a/changelog/5260.bugfix.rst b/changelog/5260.bugfix.rst
new file mode 100644
index 000000000..ab521d163
--- /dev/null
+++ b/changelog/5260.bugfix.rst
@@ -0,0 +1 @@
+Improve/fix comparison of byte strings with Python 3.
diff --git a/src/_pytest/assertion/util.py b/src/_pytest/assertion/util.py
index 762e5761d..493c630f6 100644
--- a/src/_pytest/assertion/util.py
+++ b/src/_pytest/assertion/util.py
@@ -263,8 +263,11 @@ def _compare_eq_sequence(left, right, verbose=0):
                 "At index {} diff: {!r} != {!r}".format(i, left[i], right[i])
             ]
             break
-    len_diff = len_left - len_right
 
+    if isinstance(left, bytes):
+        return explanation
+
+    len_diff = len_left - len_right
     if len_diff:
         if len_diff > 0:
             dir_with_more = "Left"
diff --git a/testing/test_assertion.py b/testing/test_assertion.py
index 0fcfd9f27..f9c67d703 100644
--- a/testing/test_assertion.py
+++ b/testing/test_assertion.py
@@ -331,6 +331,18 @@ class TestAssert_reprcompare:
         assert "- spam" in diff
         assert "+ eggs" in diff
 
+    def test_bytes_diff(self):
+        diff = callequal(b"spam", b"eggs")
+        if PY3:
+            assert diff == [
+                "b'spam' == b'eggs'",
+                "At index 0 diff: 115 != 101",
+                "Use -v to get the full diff",
+            ]
+        else:
+            # Handled as text on Python 2.
+            assert diff == ["'spam' == 'eggs'", "- spam", "+ eggs"]
+
     def test_list(self):
         expl = callequal([0, 1], [0, 2])
         assert len(expl) > 1