Update mypy error messages in code examples, part 1

docs/source/additional_features.rst

@@ -24,7 +24,7 @@ They can be defined using the :py:func:`@dataclasses.dataclass
         plugins: List[str] = field(default_factory=list)
 
     test = Application("Testing...")  # OK
-    bad = Application("Testing...", "with plugin")  # Error: List[str] expected
+    bad = Application("Testing...", "with plugin")  # error: Argument 2 to "Application" has incompatible type "str"; expected "List[str]"
 
 Mypy will detect special methods (such as :py:meth:`__lt__ <object.__lt__>`) depending on the flags used to
 define dataclasses. For example:
@@ -44,7 +44,7 @@ define dataclasses. For example:
         y: int
 
     OrderedPoint(1, 2) < OrderedPoint(3, 4)  # OK
-    UnorderedPoint(1, 2) < UnorderedPoint(3, 4)  # Error: Unsupported operand types
+    UnorderedPoint(1, 2) < UnorderedPoint(3, 4)  # error: Unsupported left operand type for < ("UnorderedPoint")
 
 Dataclasses can be generic and can be used in any other way a normal
 class can be used:
@@ -103,8 +103,8 @@ do **not** work:
       """
       attribute: int
 
-    AliasDecorated(attribute=1) # error: Unexpected keyword argument
-    DynamicallyDecorated(attribute=1) # error: Unexpected keyword argument
+    AliasDecorated(attribute=1)  # error: Unexpected keyword argument "attribute" for "AliasDecorated"
+    DynamicallyDecorated(attribute=1)  # error: Unexpected keyword argument "attribute" for "DynamicallyDecorated"
 
 .. _attrs_package:
 
@@ -153,7 +153,7 @@ That enables this to work:
     class A:
         one: int = attr.ib(8)
         two: Dict[str, str] = attr.Factory(dict)
-        bad: str = attr.ib(16)   # Error: can't assign int to str
+        bad: str = attr.ib(16)   # error: Incompatible types in assignment (expression has type "int", variable has type "str")
 
 Caveats/Known Issues
 ====================
@@ -169,7 +169,7 @@ Caveats/Known Issues
 
       import attr
       YES = True
-      @attr.s(init=YES)
+      @attr.s(init=YES)  # error: "init" argument must be True or False.
       class A:
           ...
 

docs/source/casts.rst

@@ -30,7 +30,7 @@ quite understand what is going on.
    .. code-block:: python
 
       def foo(o: object) -> None:
-          print(o + 5)  # Error: can't add 'object' and 'int'
+          print(o + 5)  # error: Unsupported operand types for + ("object" and "int")
           assert isinstance(o, int)
           print(o + 5)  # OK: type of 'o' is 'int' here
 
@@ -44,6 +44,6 @@ any operations on the result. For example:
     from typing import cast, Any
 
     x = 1
-    x.whatever()  # Type check error
+    x.whatever()  # error: "int" has no attribute "whatever"
     y = cast(Any, x)
     y.whatever()  # Type check OK (runtime error)

docs/source/class_basics.rst

@@ -21,7 +21,7 @@ initialized within the class. Mypy infers the types of attributes:
 
    a = A(1)
    a.x = 2  # OK!
-   a.y = 3  # Error: 'A' has no attribute 'y'
+   a.y = 3  # error: "A" has no attribute "y"
 
 This is a bit like each class having an implicitly defined
 :py:data:`__slots__ <object.__slots__>` attribute. This is only enforced during type
@@ -76,7 +76,7 @@ to it explicitly using ``self``:
        def __init__(self) -> None:
            self.y = 1   # Define 'y'
            a = self
-           a.x = 1      # Error: 'x' not defined
+           a.x = 1      # error: "A" has no attribute "x"
 
 Annotating __init__ methods
 ***************************
@@ -124,7 +124,7 @@ particular attribute should not be set on instances:
   A.x += 1  # OK
 
   a = A()
-  a.x = 1  # Error: Cannot assign to class variable "x" via instance
+  a.x = 1  # error: Cannot assign to class variable "x" via instance
   print(a.x)  # OK -- can be read through an instance
 
 .. note::
@@ -183,11 +183,11 @@ override has a compatible signature:
            ...
 
    class Derived1(Base):
-       def f(self, x: str) -> None:   # Error: type of 'x' incompatible
+       def f(self, x: str) -> None:   # error: Argument 1 of "f" is incompatible with supertype "Base"; supertype defines the argument type as "int"
            ...
 
    class Derived2(Base):
-       def f(self, x: int, y: int) -> None:  # Error: too many arguments
+       def f(self, x: int, y: int) -> None:  # error: Signature of "f" incompatible with supertype "Base"
            ...
 
    class Derived3(Base):
@@ -258,7 +258,7 @@ function decorator. Example:
        def can_walk(self) -> bool:
            return True
 
-   x = Animal()  # Error: 'Animal' is abstract due to 'eat' and 'can_walk'
+   x = Animal()  # error: Cannot instantiate abstract class 'Animal' with abstract attributes 'can_walk' and 'eat'
    y = Cat()     # OK
 
 .. note::

docs/source/common_issues.rst

@@ -47,8 +47,7 @@ flagged as an error.
   .. code-block:: python
 
       def foo(a: str) -> str:
-          return '(' + a.split() + ')'
-      # error: Unsupported operand types for + ("str" and List[str])
+          return '(' + a.split() + ')'  # error: Unsupported operand types for + ("str" and "List[str]")
 
   If you don't know what types to add, you can use ``Any``, but beware:
 
@@ -110,7 +109,7 @@ module:
 
 .. code-block:: python
 
-    import frobnicate  # Error: No module "frobnicate"
+    import frobnicate  # error: Cannot find module named 'frobnicate'
     frobnicate.start()
 
 You can add a ``# type: ignore`` comment to tell mypy to ignore this
@@ -234,7 +233,7 @@ with the ``Any`` type.
    def f() -> None:
        n = 1
        ...
-       n = 'x'        # Type error: n has type int
+       n = 'x'  # error: Incompatible types in assignment (expression has type "str", variable has type "int")
 
 .. note::
 
@@ -270,7 +269,8 @@ unexpected errors when combined with type inference. For example:
 
    lst = [A(), A()]  # Inferred type is List[A]
    new_lst = [B(), B()]  # inferred type is List[B]
-   lst = new_lst  # mypy will complain about this, because List is invariant
+   # mypy will complain about this, because List is invariant
+   lst = new_lst  # error: Incompatible types in assignment (expression has type "List[B]", variable has type "List[A]")
 
 Possible strategies in such situations are:
 
@@ -582,7 +582,7 @@ the same line as the import:
 
    # to silence complaints about unused imports
    from typing import List  # noqa
-   a = None  # type: List[int]
+   a = []  # type: List[int]
 
 
 To silence the linter on the same line as a type comment
@@ -611,7 +611,7 @@ Consider this example:
    class C:
        x = 42
    c = C()
-   fun(c)  # This is not safe
+   fun(c)  # This is not safe:  # error: Argument 1 to "fun" has incompatible type "C"; expected "P"
    c.x << 5  # Since this will fail!
 
 To work around this problem consider whether "mutating" is actually part
@@ -646,7 +646,7 @@ method signature.  E.g.:
    class Message:
        def bytes(self):
            ...
-       def register(self, path: bytes):  # error: Invalid type "mod.Message.bytes"
+       def register(self, path: bytes):  # error: Function "__main__.Message.bytes" is not valid as a type
            ...
 
 The third line elicits an error because mypy sees the argument type