Allow tuples as second argument to namedtuple

mypy/semanal.py

@@ -1634,14 +1634,14 @@ def parse_namedtuple_args(self, call: CallExpr,
                 "namedtuple() expects a string literal as the first argument", call)
         types = []  # type: List[Type]
         ok = True
-        if not isinstance(args[1], ListExpr):
+        if not isinstance(args[1], (ListExpr, TupleExpr)):
             if (fullname == 'collections.namedtuple'
                     and isinstance(args[1], (StrExpr, BytesExpr, UnicodeExpr))):
                 str_expr = cast(StrExpr, args[1])
                 items = str_expr.value.replace(',', ' ').split()
             else:
                 return self.fail_namedtuple_arg(
-                    "List literal expected as the second argument to namedtuple()", call)
+                    "List or tuple literal expected as the second argument to namedtuple()", call)
         else:
             listexpr = args[1]
             if fullname == 'collections.namedtuple':

test-data/unit/check-namedtuple.test

@@ -9,6 +9,17 @@ a = x[1]
 a, b, c = x # E: Need more than 2 values to unpack (3 expected)
 x[2] # E: Tuple index out of range
 
+[case testNamedTupleWithTupleFieldNamesUsedAsTuple]
+from collections import namedtuple
+
+X = namedtuple('X', ('x', 'y'))
+x = None  # type: X
+a, b = x
+b = x[0]
+a = x[1]
+a, b, c = x # E: Need more than 2 values to unpack (3 expected)
+x[2] # E: Tuple index out of range
+
 [case testNamedTupleNoUnderscoreFields]
 from collections import namedtuple
 
@@ -82,6 +93,19 @@ x, y = n
 x = y  # E: Incompatible types in assignment (expression has type "str", variable has type "int")
 
 
+[case testNamedTupleWithTupleFieldNamesWithItemTypes]
+from typing import NamedTuple
+N = NamedTuple('N', (('a', int),
+                     ('b', str)))
+n = N(1, 'x')
+s = n.a # type: str  # E: Incompatible types in assignment (expression has type "int", \
+                          variable has type "str")
+i = n.b # type: int  # E: Incompatible types in assignment (expression has type "str", \
+                          variable has type "int")
+x, y = n
+x = y  # E: Incompatible types in assignment (expression has type "str", variable has type "int")
+
+
 [case testNamedTupleConstructorArgumentTypes]
 from typing import NamedTuple
 N = NamedTuple('N', [('a', int),

test-data/unit/semanal-namedtuple.test

@@ -32,6 +32,22 @@ MypyFile:1(
     Block:3(
       PassStmt:3())))
 
+[case testTwoItemNamedtupleWithTupleFieldNames]
+from collections import namedtuple
+N = namedtuple('N', ('a', 'xyz'))
+def f() -> N: pass
+[out]
+MypyFile:1(
+  ImportFrom:1(collections, [namedtuple])
+  AssignmentStmt:2(
+    NameExpr(N* [__main__.N])
+    NamedTupleExpr:2(N, Tuple[Any, Any]))
+  FuncDef:3(
+    f
+    def () -> Tuple[Any, Any, fallback=__main__.N]
+    Block:3(
+      PassStmt:3())))
+
 [case testTwoItemNamedtupleWithShorthandSyntax]
 from collections import namedtuple
 N = namedtuple('N', ' a  xyz ')
@@ -59,6 +75,17 @@ MypyFile:1(
     NameExpr(N* [__main__.N])
     NamedTupleExpr:2(N, Tuple[builtins.int, builtins.str])))
 
+[case testNamedTupleWithTupleFieldNamesWithItemTypes]
+from typing import NamedTuple
+N = NamedTuple('N', (('a', int),
+                     ('b', str)))
+[out]
+MypyFile:1(
+  ImportFrom:1(typing, [NamedTuple])
+  AssignmentStmt:2(
+    NameExpr(N* [__main__.N])
+    NamedTupleExpr:2(N, Tuple[builtins.int, builtins.str])))
+
 [case testNamedTupleBaseClass]
 from collections import namedtuple
 N = namedtuple('N', ['x'])
@@ -121,7 +148,7 @@ N = namedtuple(1, ['x']) # E: namedtuple() expects a string literal as the first
 
 [case testNamedTupleWithInvalidItems]
 from collections import namedtuple
-N = namedtuple('N', 1) # E: List literal expected as the second argument to namedtuple()
+N = namedtuple('N', 1) # E: List or tuple literal expected as the second argument to namedtuple()
 
 [case testNamedTupleWithInvalidItems2]
 from collections import namedtuple