Add comments and more tests

Author: pkch

mypy/checker.py

@@ -1940,11 +1940,13 @@ def visit_operator_assignment_stmt(self,
         lvalue_type = self.expr_checker.accept(s.lvalue)
         inplace, method = infer_operator_assignment_method(lvalue_type, s.op)
         if inplace:
+            # There is __ifoo__, treat as x = x.__ifoo__(y)
             rvalue_type, method_type = self.expr_checker.check_op(
                 method, lvalue_type, s.rvalue, s)
             if not is_subtype(rvalue_type, lvalue_type):
                 self.msg.incompatible_operator_assignment(s.op, s)
         else:
+            # There is no __ifoo__, treat as x = x <foo> y
             expr = OpExpr(s.op, s.lvalue, s.rvalue)
             expr.set_line(s)
             self.check_assignment(lvalue=s.lvalue, rvalue=expr,

test-data/unit/check-statements.test

@@ -1524,5 +1524,36 @@ weight0 *= 'a'  # E: Incompatible types in assignment (expression has type "str"
 weight0 *= 0.5
 reveal_type(weight0)  # E: Revealed type is 'builtins.float'
 weight0 *= object()  # E: Unsupported operand types for * ("float" and "object")
+reveal_type(weight0) # E: Revealed type is 'builtins.float'
 
 [builtins fixtures/float.pyi]
+
+[case testAugmentedAssignmentIntFloatMember]
+class A:
+    def __init__(self) -> None:
+        self.weight0 = 65.5
+        reveal_type(self.weight0)  # E: Revealed type is 'builtins.float'
+        self.weight0 = 65
+        reveal_type(self.weight0)  # E: Revealed type is 'builtins.int'
+        self.weight0 *= 'a'  # E: Incompatible types in assignment (expression has type "str", variable has type "float")
+        self.weight0 *= 0.5
+        reveal_type(self.weight0)  # E: Revealed type is 'builtins.float'
+        self.weight0 *= object()  # E: Unsupported operand types for * ("float" and "object")
+        reveal_type(self.weight0) # E: Revealed type is 'builtins.float'
+
+[builtins fixtures/float.pyi]
+
+[case testAugmentedAssignmentIntFloatDict]
+from typing import Dict
+d = {'weight0': 65.5}
+reveal_type(d['weight0'])  # E: Revealed type is 'builtins.float*'
+d['weight0'] = 65
+reveal_type(d['weight0'])  # E: Revealed type is 'builtins.float*'
+d['weight0'] *= 'a'  # E: Unsupported operand types for * ("float" and "str") # E: Incompatible types in assignment (expression has type "str", target has type "float")
+d['weight0'] *= 0.5
+reveal_type(d['weight0'])  # E: Revealed type is 'builtins.float*'
+d['weight0'] *= object()  # E: Unsupported operand types for * ("float" and "object")
+reveal_type(d['weight0']) # E: Revealed type is 'builtins.float*'
+
+[builtins fixtures/floatdict.pyi]
+