Skip arg count checks for dynamic functions.

Author: Guido van Rossum

mypy/checkexpr.py

@@ -238,8 +238,9 @@ def check_call(self, callee: Type, args: List[Node],
             arg_types = self.infer_arg_types_in_context2(
                 callee, args, arg_kinds, formal_to_actual)
 
-            self.check_argument_count(callee, arg_types, arg_kinds,
-                                      arg_names, formal_to_actual, context, self.msg)
+            if self.chk.typing_mode_full():
+                self.check_argument_count(callee, arg_types, arg_kinds,
+                                          arg_names, formal_to_actual, context, self.msg)
 
             self.check_argument_types(arg_types, arg_kinds, callee,
                                       formal_to_actual, context,

mypy/test/data/check-dynamic-typing.test

@@ -655,3 +655,25 @@ class A(B):
         x()
 [out]
 main: note: In class "A":
+
+
+-- Don't complain about too few/many arguments in dynamic functions
+-- ----------------------------------------------------------------
+
+[case testTooManyArgsInDynamic]
+def f() -> None: pass
+def g():
+    f(1) # Silent
+[out]
+
+[case testTooFewArgsInDynamic]
+def f(a: int) -> None: pass
+def g():
+    f() # Silent
+[out]
+
+[case testJustRightInDynamic]
+def f(a: int) -> None: pass
+def g():
+    f('') # Silent
+[out]