Merge branch 'abstract-property'

Implement @abstractproperty. Closes #263.

Author: JukkaL

mypy/checker.py

@@ -1898,6 +1898,20 @@ def visit_decorator(self, e: Decorator) -> Type:
         sig = set_callable_name(sig, e.func)
         e.var.type = sig
         e.var.is_ready = True
+        if e.func.is_property:
+            self.check_incompatible_property_override(e)
+
+    def check_incompatible_property_override(self, e: Decorator) -> None:
+        if not e.var.is_settable_property:
+            name = e.func.name()
+            for base in e.func.info.mro[1:]:
+                base_attr = base.names.get(name)
+                if not base_attr:
+                    continue
+                if (isinstance(base_attr.node, OverloadedFuncDef) and
+                        base_attr.node.is_property and
+                        base_attr.node.items[0].var.is_settable_property):
+                    self.fail(messages.READ_ONLY_PROPERTY_OVERRIDES_READ_WRITE, e)
 
     def visit_with_stmt(self, s: WithStmt) -> Type:
         echk = self.expr_checker

mypy/messages.py

@@ -64,6 +64,8 @@
 CANNOT_ASSIGN_TO_TYPE = 'Cannot assign to a type'
 INCONSISTENT_ABSTRACT_OVERLOAD = \
     'Overloaded method has both abstract and non-abstract variants'
+READ_ONLY_PROPERTY_OVERRIDES_READ_WRITE = \
+    'Read-only property cannot override read-write property'
 INSTANCE_LAYOUT_CONFLICT = 'Instance layout conflict in multiple inheritance'
 FORMAT_REQUIRES_MAPPING = 'Format requires a mapping'
 GENERIC_TYPE_NOT_VALID_AS_EXPRESSION = \
@@ -732,7 +734,7 @@ def cannot_instantiate_abstract_class(self, class_name: str,
                                           context: Context) -> None:
         attrs = format_string_list("'%s'" % a for a in abstract_attributes[:5])
         self.fail("Cannot instantiate abstract class '%s' with abstract "
-                  "method%s %s" % (class_name, plural_s(abstract_attributes),
+                  "attribute%s %s" % (class_name, plural_s(abstract_attributes),
                                    attrs),
                   context)
 

mypy/semanal.py

@@ -424,6 +424,8 @@ def analyze_property_with_multi_part_definition(self, defn: OverloadedFuncDef) -
                     if node.name == 'setter':
                         # The first item represents the entire property.
                         defn.items[0].var.is_settable_property = True
+                        # Get abstractness from the original definition.
+                        item.func.is_abstract = items[0].func.is_abstract
             else:
                 self.fail("Decorated property not supported", item)
             item.func.accept(self)
@@ -1498,10 +1500,13 @@ def visit_decorator(self, dec: Decorator) -> None:
                 dec.func.is_class = True
                 dec.var.is_classmethod = True
                 self.check_decorated_function_is_method('classmethod', dec)
-            elif refers_to_fullname(d, 'builtins.property'):
+            elif (refers_to_fullname(d, 'builtins.property') or
+                  refers_to_fullname(d, 'abc.abstractproperty')):
                 removed.append(i)
                 dec.func.is_property = True
                 dec.var.is_property = True
+                if refers_to_fullname(d, 'abc.abstractproperty'):
+                    dec.func.is_abstract = True
                 self.check_decorated_function_is_method('property', dec)
                 if len(dec.func.arguments) > 1:
                     self.fail('Too many arguments', dec.func)
@@ -2353,10 +2358,17 @@ def visit_decorator(self, dec: Decorator) -> None:
         """
         super().visit_decorator(dec)
         if dec.var.is_property:
+            # Decorators are expected to have a callable type (it's a little odd).
             if dec.func.type is None:
-                dec.var.type = AnyType()
+                dec.var.type = CallableType(
+                    [AnyType()],
+                    [ARG_POS],
+                    [None],
+                    AnyType(),
+                    self.builtin_type('function'),
+                    name=dec.var.name())
             elif isinstance(dec.func.type, CallableType):
-                dec.var.type = dec.func.type.ret_type
+                dec.var.type = dec.func.type
             return
         decorator_preserves_type = True
         for expr in dec.decorators:

mypy/test/data/check-abstract.test

@@ -142,7 +142,7 @@ class B(metaclass=ABCMeta):
   @abstractmethod
   def f(self): pass
 A() # OK
-B() # E: Cannot instantiate abstract class 'B' with abstract method 'f'
+B() # E: Cannot instantiate abstract class 'B' with abstract attribute 'f'
 [out]
 
 [case testInstantiatingClassWithInheritedAbstractMethod]
@@ -154,7 +154,7 @@ class A(metaclass=ABCMeta):
   @abstractmethod
   def g(self): pass
 class B(A): pass
-B()# E: Cannot instantiate abstract class 'B' with abstract methods 'f' and 'g'
+B()# E: Cannot instantiate abstract class 'B' with abstract attributes 'f' and 'g'
 [out]
 
 
@@ -376,8 +376,8 @@ class D(A, B):
 class E(A, B):
   def f(self) -> None: pass
   def g(self) -> None: pass
-C() # E: Cannot instantiate abstract class 'C' with abstract method 'g'
-D() # E: Cannot instantiate abstract class 'D' with abstract method 'f'
+C() # E: Cannot instantiate abstract class 'C' with abstract attribute 'g'
+D() # E: Cannot instantiate abstract class 'D' with abstract attribute 'f'
 E()
 
 [case testInconsistentMro]
@@ -405,7 +405,7 @@ class B(A):
   def f(self, x: int) -> int: pass
   @overload
   def f(self, x: str) -> str: pass
-A() # E: Cannot instantiate abstract class 'A' with abstract method 'f'
+A() # E: Cannot instantiate abstract class 'A' with abstract attribute 'f'
 B()
 B().f(1)
 a = B() # type: A
@@ -430,7 +430,7 @@ class B(A):
   def f(self, x: int) -> int: pass
   @overload
   def f(self, x: str) -> str: pass
-A() # E: Cannot instantiate abstract class 'A' with abstract method 'f'
+A() # E: Cannot instantiate abstract class 'A' with abstract attribute 'f'
 B()
 B().f(1)
 a = B() # type: A
@@ -521,3 +521,211 @@ class B:
 class C:
     def __add__(self, other: int) -> B: pass
 [out]
+
+
+-- Abstract properties
+-- -------------------
+
+
+[case testReadOnlyAbstractProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+def f(a: A) -> None:
+    a.x() # E: "int" not callable
+    a.x = 1  # E: Property "x" defined in "A" is read-only
+[out]
+main: note: In function "f":
+
+[case testReadOnlyAbstractPropertyForwardRef]
+from abc import abstractproperty, ABCMeta
+def f(a: A) -> None:
+    a.x() # E: "int" not callable
+    a.x = 1  # E: Property "x" defined in "A" is read-only
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+[out]
+main: note: In function "f":
+
+[case testReadWriteAbstractProperty]
+from abc import abstractproperty, ABCMeta
+def f(a: A) -> None:
+    a.x.y # E: "int" has no attribute "y"
+    a.x = 1
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+    @x.setter
+    def x(self, x: int) -> None: pass
+[out]
+main: note: In function "f":
+
+[case testInstantiateClassWithReadOnlyAbstractProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+class B(A): pass
+b = B() # E: Cannot instantiate abstract class 'B' with abstract attribute 'x'
+
+[case testInstantiateClassWithReadWriteAbstractProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+    @x.setter
+    def x(self, x: int) -> None: pass
+class B(A): pass
+b = B() # E: Cannot instantiate abstract class 'B' with abstract attribute 'x'
+
+[case testImplementAbstractPropertyViaProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+class B(A):
+    @property
+    def x(self) -> int: pass
+b = B()
+b.x() # E: "int" not callable
+[builtins fixtures/property.py]
+
+[case testImplementReradWriteAbstractPropertyViaProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+    @x.setter
+    def x(self, v: int) -> None: pass
+class B(A):
+    @property
+    def x(self) -> int: pass
+    @x.setter
+    def x(self, v: int) -> None: pass
+b = B()
+b.x.y # E: "int" has no attribute "y"
+[builtins fixtures/property.py]
+
+[case testImplementAbstractPropertyViaPropertyInvalidType]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+class B(A):
+    @property
+    def x(self) -> str: pass # E
+b = B()
+b.x() # E
+[builtins fixtures/property.py]
+[out]
+main: note: In class "B":
+main:7: error: Return type of "x" incompatible with supertype "A"
+main: note: At top level:
+main:9: error: "str" not callable
+
+[case testCantImplementAbstractPropertyViaInstanceVariable]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+class B(A):
+    def __init__(self) -> None:
+        self.x = 1 # E
+b = B() # E
+b.x.y # E
+[builtins fixtures/property.py]
+[out]
+main: note: In member "__init__" of class "B":
+main:7: error: Property "x" defined in "B" is read-only
+main: note: At top level:
+main:8: error: Cannot instantiate abstract class 'B' with abstract attribute 'x'
+main:9: error: "int" has no attribute "y"
+
+[case testSuperWithAbstractProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+class B(A):
+    @property
+    def x(self) -> int:
+        return super().x.y # E: "int" has no attribute "y"
+[builtins fixtures/property.py]
+[out]
+main: note: In member "x" of class "B":
+
+[case testSuperWithReadWriteAbstractProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+    @x.setter
+    def x(self, v: int) -> None: pass
+class B(A):
+    @property
+    def x(self) -> int:
+        return super().x.y # E
+    @x.setter
+    def x(self, v: int) -> None:
+        super().x = '' # E
+[builtins fixtures/property.py]
+[out]
+main: note: In member "x" of class "B":
+main:10: error: "int" has no attribute "y"
+main: note: In function "x":
+main:13: error: Invalid assignment target
+
+[case testOnlyImplementGetterOfReadWriteAbstractProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+    @x.setter
+    def x(self, v: int) -> None: pass
+class B(A):
+    @property # E
+    def x(self) -> int: pass
+b = B()
+b.x.y # E
+[builtins fixtures/property.py]
+[out]
+main: note: In class "B":
+main:8: error: Read-only property cannot override read-write property
+main: note: At top level:
+main:11: error: "int" has no attribute "y"
+
+[case testDynamicallyTypedReadOnlyAbstractProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self): pass
+def f(a: A) -> None:
+    a.x.y
+    a.x = 1  # E: Property "x" defined in "A" is read-only
+[out]
+main: note: In function "f":
+
+[case testDynamicallyTypedReadOnlyAbstractPropertyForwardRef]
+from abc import abstractproperty, ABCMeta
+def f(a: A) -> None:
+    a.x.y
+    a.x = 1  # E: Property "x" defined in "A" is read-only
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self): pass
+[out]
+main: note: In function "f":
+
+[case testDynamicallyTypedReadWriteAbstractProperty]
+from abc import abstractproperty, ABCMeta
+def f(a: A) -> None:
+    a.x.y
+    a.x = 1
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self): pass
+    @x.setter
+    def x(self, x): pass
+[out]

mypy/test/data/lib-stub/abc.py

@@ -1,2 +1,3 @@
 class ABCMeta: pass
 abstractmethod = object()
+abstractproperty = object()

mypy/test/data/python2eval.test

@@ -379,3 +379,19 @@ _program.py:2: error: No overload variant of "f" matches argument types [builtin
 def f(x): # type: (str) -> None
     pass
 f(bytearray('foo'))
+
+[case testAbstractProperty_python2]
+from abc import abstractproperty, ABCMeta
+class A:
+    __metaclass__ = ABCMeta
+    @abstractproperty
+    def x(self): # type: () -> int
+        pass
+class B(A):
+    @property
+    def x(self): # type: () -> int
+        return 3
+b = B()
+print b.x + 1
+[out]
+4

mypy/test/data/pythoneval.test

@@ -943,7 +943,6 @@ print(r"""\"""$""")
 [out]
 '
 \"""$
---' (hack to fix syntax highlighting)
 
 [case testSubclassBothGenericAndNonGenericABC]
 from typing import Generic, TypeVar
@@ -1103,3 +1102,17 @@ T = TypeVar('T')
 def sorted(x: Iterable[T], *, key: Callable[[T], object] = None) -> None: ...
 a = None # type: List[Dict[str, str]]
 sorted(a, key=lambda y: y[''])
+
+[case testAbstractProperty]
+from abc import abstractproperty, ABCMeta
+class A(metaclass=ABCMeta):
+    @abstractproperty
+    def x(self) -> int: pass
+class B(A):
+    @property
+    def x(self) -> int:
+        return 3
+b = B()
+print(b.x + 1)
+[out]
+4