Add support to display field names in namedtuple diffs.

AUTHORS

@@ -155,6 +155,7 @@ Justyna Janczyszyn
 Kale Kundert
 Kamran Ahmad
 Karl O. Pinc
+Karthikeyan Singaravelan
 Katarzyna Jachim
 Katarzyna Król
 Katerina Koukiou

changelog/7527.improvement.rst

@@ -0,0 +1 @@
+When a comparison between `namedtuple` instances of the same type fails, pytest now shows the differing field names (possibly nested) instead of their indexes.

src/_pytest/assertion/util.py

@@ -110,6 +110,10 @@ def isset(x: Any) -> bool:
     return isinstance(x, (set, frozenset))
 
 
+def isnamedtuple(obj: Any) -> bool:
+    return isinstance(obj, tuple) and getattr(obj, "_fields", None) is not None
+
+
 def isdatacls(obj: Any) -> bool:
     return getattr(obj, "__dataclass_fields__", None) is not None
 
@@ -171,14 +175,20 @@ def _compare_eq_any(left: Any, right: Any, verbose: int = 0) -> List[str]:
     if istext(left) and istext(right):
         explanation = _diff_text(left, right, verbose)
     else:
-        if issequence(left) and issequence(right):
+        if type(left) == type(right) and (
+            isdatacls(left) or isattrs(left) or isnamedtuple(left)
+        ):
+            # Note: unlike dataclasses/attrs, namedtuples compare only the
+            # field values, not the type or field names. But this branch
+            # intentionally only handles the same-type case, which was often
+            # used in older code bases before dataclasses/attrs were available.
+            explanation = _compare_eq_cls(left, right, verbose)
+        elif issequence(left) and issequence(right):
             explanation = _compare_eq_sequence(left, right, verbose)
         elif isset(left) and isset(right):
             explanation = _compare_eq_set(left, right, verbose)
         elif isdict(left) and isdict(right):
             explanation = _compare_eq_dict(left, right, verbose)
-        elif type(left) == type(right) and (isdatacls(left) or isattrs(left)):
-            explanation = _compare_eq_cls(left, right, verbose)
         elif verbose > 0:
             explanation = _compare_eq_verbose(left, right)
         if isiterable(left) and isiterable(right):
@@ -408,6 +418,10 @@ def _compare_eq_cls(left: Any, right: Any, verbose: int) -> List[str]:
     elif isattrs(left):
         all_fields = left.__attrs_attrs__
         fields_to_check = [field.name for field in all_fields if getattr(field, "eq")]
+    elif isnamedtuple(left):
+        fields_to_check = left._fields
+    else:
+        assert False
 
     indent = "  "
     same = []

testing/test_assertion.py

@@ -1,3 +1,4 @@
+import collections
 import sys
 import textwrap
 from typing import Any
@@ -987,6 +988,44 @@ class TestAssert_reprcompare_attrsclass:
         assert lines is None
 
 
+class TestAssert_reprcompare_namedtuple:
+    def test_namedtuple(self) -> None:
+        NT = collections.namedtuple("NT", ["a", "b"])
+
+        left = NT(1, "b")
+        right = NT(1, "c")
+
+        lines = callequal(left, right)
+        assert lines == [
+            "NT(a=1, b='b') == NT(a=1, b='c')",
+            "",
+            "Omitting 1 identical items, use -vv to show",
+            "Differing attributes:",
+            "['b']",
+            "",
+            "Drill down into differing attribute b:",
+            "  b: 'b' != 'c'",
+            "  - c",
+            "  + b",
+            "Use -v to get the full diff",
+        ]
+
+    def test_comparing_two_different_namedtuple(self) -> None:
+        NT1 = collections.namedtuple("NT1", ["a", "b"])
+        NT2 = collections.namedtuple("NT2", ["a", "b"])
+
+        left = NT1(1, "b")
+        right = NT2(2, "b")
+
+        lines = callequal(left, right)
+        # Because the types are different, uses the generic sequence matcher.
+        assert lines == [
+            "NT1(a=1, b='b') == NT2(a=2, b='b')",
+            "At index 0 diff: 1 != 2",
+            "Use -v to get the full diff",
+        ]
+
+
 class TestFormatExplanation:
     def test_special_chars_full(self, pytester: Pytester) -> None:
         # Issue 453, for the bug this would raise IndexError