Now print >> is properly checked (#11576)

Author: sobolevn

mypy/checker.py

@@ -3938,8 +3938,21 @@ def visit_print_stmt(self, s: PrintStmt) -> None:
         if s.target:
             target_type = get_proper_type(self.expr_checker.accept(s.target))
             if not isinstance(target_type, NoneType):
-                # TODO: Also verify the type of 'write'.
-                self.expr_checker.analyze_external_member_access('write', target_type, s.target)
+                write_type = self.expr_checker.analyze_external_member_access(
+                    'write', target_type, s.target)
+                required_type = CallableType(
+                    arg_types=[self.named_type('builtins.str')],
+                    arg_kinds=[ARG_POS],
+                    arg_names=[None],
+                    ret_type=AnyType(TypeOfAny.implementation_artifact),
+                    fallback=self.named_type('builtins.function'),
+                )
+                # This has to be hard-coded, since it is a syntax pattern, not a function call.
+                if not is_subtype(write_type, required_type):
+                    self.fail(message_registry.PYTHON2_PRINT_FILE_TYPE.format(
+                        write_type,
+                        required_type,
+                    ), s.target)
 
     def visit_break_stmt(self, s: BreakStmt) -> None:
         self.binder.handle_break()

mypy/message_registry.py

@@ -135,6 +135,9 @@ def format(self, *args: object, **kwargs: object) -> "ErrorMessage":
     code=codes.TRUTHY_BOOL,
 )
 NOT_CALLABLE: Final = '{} not callable'
+PYTHON2_PRINT_FILE_TYPE: Final = (
+    'Argument "file" to "print" has incompatible type "{}"; expected "{}"'
+)
 
 # Generic
 GENERIC_INSTANCE_VAR_CLASS_ACCESS: Final = (

test-data/unit/check-python2.test

@@ -27,10 +27,16 @@ class A:
         # type: (str) -> None
         pass
 
+class B:
+    def write(self):
+        # type: () -> int
+        pass
+
 print >>A(), ''
 print >>None, ''
 print >>1, '' # E: "int" has no attribute "write"
 print >>(None + ''), None # E: Unsupported left operand type for + ("None")
+print >> B(), ''  # E: Argument "file" to "print" has incompatible type "def () -> builtins.int"; expected "def (builtins.str) -> Any"
 
 [case testDivision]
 class A: