List.__eq__ doesn't raise on non-Sized

Summary:
In general, comparison operators shouldn't raise on a type mismatch; instead `__eq__` should return `False` and `__ne__` should return `True`. The behavior for `__lt__` etc. is ambiguous, so leaving that unchanged.

This diff adds a `Sized` check to return `False` early in equality check. It also splits the `list_compare` method into `list_eq` and `list_lt` to make these easier to understand and improve performance (e.g., less branching inside `for` loop).

V2: had # / buildall

Reviewed By: yoney

Differential Revision: D64998005

fbshipit-source-id: d99e45784b4e16d2b45e434ef30e89a167ece778

thrift/lib/py3/test/auto_migrate/lists.py

@@ -165,6 +165,14 @@ def test_comparisons(self) -> None:
         #  got `List__i32`.
         self.assertGreaterEqual(x, x2)
 
+    @brokenInAutoMigrate()
+    def test_no_raise_on_type_error(self) -> None:
+        t_list = I32List([1, 2, 3, 4])
+        self.assertFalse(t_list == easy())
+        self.assertFalse(easy() == t_list)
+        self.assertNotEqual(t_list, easy())
+        self.assertNotEqual(easy(), t_list)
+
     @brokenInAutoMigrate()
     def test_is_container(self) -> None:
         self.assertIsInstance(int_list, Container)

thrift/lib/py3/types.pyx

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 from collections import defaultdict
-from collections.abc import Iterable, Mapping, Set as pySet
+from collections.abc import Iterable, Mapping, Set as pySet, Sized
 import enum
 import itertools
 import warnings
@@ -46,29 +46,29 @@ __all__ = ['Struct', 'BadEnum', 'Union', 'Enum', 'Flag', 'EnumMeta']
 Object = cython.fused_type(Struct, GeneratedError)
 
 
+cdef list_eq(List self, object other):
+    if (
+        not isinstance(other, Iterable) or
+        not isinstance(other, Sized) or
+        len(self) != len(other)
+    ):
+        return False
 
-cdef list_compare(object first, object second, int op):
-    """ Take either Py_EQ or Py_LT, everything else is derived """
-    if not (isinstance(first, Iterable) and isinstance(second, Iterable)):
-        if op == Py_EQ:
+    for x, y in zip(self, other):
+        if x != y:
             return False
-        else:
-            return NotImplemented
+    return True
 
-    if op == Py_EQ:
-        if len(first) != len(second):
-            return False
+
+cdef list_lt(object first, object second):
+    if not (isinstance(first, Iterable) and isinstance(second, Iterable)):
+        return NotImplemented
 
     for x, y in zip(first, second):
         if x != y:
-            if op == Py_LT:
-                return x < y
-            else:
-                return False
+            return x < y
 
-    if op == Py_LT:
-        return len(first) < len(second)
-    return True
+    return len(first) < len(second)
 
 
 @cython.internal
@@ -318,24 +318,30 @@ cdef class List(Container):
         return type(other)(itertools.chain(other, self))
 
     def __eq__(self, other):
-        return list_compare(self, other, Py_EQ)
+        return list_eq(self, other)
 
     def __ne__(self, other):
-        return not list_compare(self, other, Py_EQ)
+        return not list_eq(self, other)
 
     def __lt__(self, other):
-        return list_compare(self, other, Py_LT)
+        return list_lt(self, other)
 
     def __gt__(self, other):
-        return list_compare(other, self, Py_LT)
+        return list_lt(other, self)
 
     def __le__(self, other):
-        result = list_compare(other, self, Py_LT)
-        return not result if result is not NotImplemented else NotImplemented
+        result = list_lt(other, self)
+        if result is NotImplemented:
+            return NotImplemented
+
+        return not result
 
     def __ge__(self, other):
-        result = list_compare(self, other, Py_LT)
-        return not result if result is not NotImplemented else NotImplemented
+        result = list_lt(self, other)
+        if result is NotImplemented:
+            return NotImplemented
+
+        return not result
 
     def __repr__(self):
         if not self: