Speed up __eq__

changelog.d/1310.breaking.md

@@ -0,0 +1,3 @@
+Speed up the generated `__eq__` methods significantly by generating a chain of attribute comparisons instead of constructing and comparing tuples.
+This change arguably makes the behavior more correct,
+but changes it if an attribute compares equal by identity but not value, like `float('nan')`.

docs/comparison.md

@@ -5,7 +5,10 @@ For that, *attrs* writes `__eq__` and `__ne__` methods for you.
 
 Additionally, if you pass `order=True`, *attrs* will also create a complete set of ordering methods: `__le__`, `__lt__`, `__ge__`, and `__gt__`.
 
-Both for equality and order, *attrs* will:
+For equality, *attrs* will generate a statement comparing the types of both instances,
+and then comparing each attribute in turn using `==`.
+
+For order, *attrs* will:
 
 - Check if the types of the instances you're comparing are equal,
 - if so, create a tuple of all field values for each instance,

src/attr/_make.py

@@ -1864,20 +1864,20 @@ def _make_eq(cls, attrs):
     globs = {}
     if attrs:
         lines.append("    return  (")
-        others = ["    ) == ("]
         for a in attrs:
             if a.eq_key:
                 cmp_name = f"_{a.name}_key"
                 # Add the key function to the global namespace
                 # of the evaluated function.
                 globs[cmp_name] = a.eq_key
-                lines.append(f"        {cmp_name}(self.{a.name}),")
-                others.append(f"        {cmp_name}(other.{a.name}),")
+                lines.append(
+                    f"        {cmp_name}(self.{a.name}) == {cmp_name}(other.{a.name})"
+                )
             else:
-                lines.append(f"        self.{a.name},")
-                others.append(f"        other.{a.name},")
-
-        lines += [*others, "    )"]
+                lines.append(f"        self.{a.name} == other.{a.name}")
+            if a is not attrs[-1]:
+                lines[-1] = f"{lines[-1]} and"
+        lines.append("    )")
     else:
         lines.append("    return True")
 

tests/strategies.py

@@ -75,7 +75,7 @@ def _create_hyp_nested_strategy(draw, simple_class_strategy):
 bare_attrs = st.builds(attr.ib, default=st.none())
 int_attrs = st.integers().map(lambda i: attr.ib(default=i))
 str_attrs = st.text().map(lambda s: attr.ib(default=s))
-float_attrs = st.floats().map(lambda f: attr.ib(default=f))
+float_attrs = st.floats(allow_nan=False).map(lambda f: attr.ib(default=f))
 dict_attrs = st.dictionaries(keys=st.text(), values=st.integers()).map(
     lambda d: attr.ib(default=d)
 )