Make type of *args argument Sequence instead of list

Closes #261.

Author: JukkaL

mypy/checker.py

@@ -517,7 +517,8 @@ def check_func_def(self, defn: FuncItem, typ: CallableType, name: str) -> None:
             for i in range(len(typ.arg_types)):
                 arg_type = typ.arg_types[i]
                 if typ.arg_kinds[i] == nodes.ARG_STAR:
-                    arg_type = self.named_generic_type('builtins.list',
+                    # TODO: This should actually be Tuple[t, ...] once it's supported.
+                    arg_type = self.named_generic_type('typing.Sequence',
                                                        [arg_type])
                 elif typ.arg_kinds[i] == nodes.ARG_STAR2:
                     arg_type = self.named_generic_type('builtins.dict',

mypy/test/data/check-varargs.test

@@ -6,12 +6,12 @@
 
 
 [case testVarArgsWithinFunction]
-from typing import Undefined, List
+from typing import Undefined, Sequence
 def f( *b: 'B') -> None:
-    ab = Undefined # type: List[B]
-    ac = Undefined # type: List[C]
-    b = ac # E: Incompatible types in assignment (expression has type List[C], variable has type List[B])
-    ac = b # E: Incompatible types in assignment (expression has type List[B], variable has type List[C])
+    ab = Undefined # type: Sequence[B]
+    ac = Undefined # type: Sequence[C]
+    b = ac # E: Incompatible types in assignment (expression has type Sequence[C], variable has type Sequence[B])
+    ac = b # E: Incompatible types in assignment (expression has type Sequence[B], variable has type Sequence[C])
     b = ab
     ab = b
 

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

@@ -32,3 +32,7 @@ def __iter__(self) -> 'Iterator[T]': pass
 class Iterator(Iterable[T], Generic[T]):
     @abstractmethod
     def __next__(self) -> T: pass
+
+class Sequence(Generic[T]):
+    @abstractmethod
+    def __getitem__(self, n: Any) -> T: pass

mypy/test/data/pythoneval.test

@@ -993,3 +993,12 @@ def f() -> Optional[int]: pass
 x = f()
 y = 1
 y = x
+
+[case testAppendToStarArg]
+import typing
+def f(*x: int) -> None:
+    x.append(1)
+f(1)
+[out]
+_program.py: In function "f":
+_program.py, line 3: Sequence[int] has no attribute "append"

mypy/test/testtypes.py

@@ -237,7 +237,7 @@ def callable(self, vars, *a) -> CallableType:
         for v in vars:
             tv.append(TypeVarDef(v, n, None, self.fx.o))
             n -= 1
-        return CallableType(a[:-1],
+        return CallableType(list(a[:-1]),
                         [ARG_POS] * (len(a) - 1),
                         [None] * (len(a) - 1),
                         a[-1],