Make untyped mutating callbacks work

src/callback.jl

@@ -15,9 +15,22 @@
 
 # convert Python args to Julia; overridden below for a FuncWrapper type
 # that allows the user to specify the argument types.
-julia_args(f, args) = convert(PyAny, args)
+julia_args(f, args) =
+    [_julia_arg(_getindex(args, i, PyObject)) for i in 1:length(args)]
 julia_kwarg(f, kw, arg) = convert(PyAny, arg)
 
+# For mutating functions such as fill! to mutate Python objects,
+# arguments have to be wrapped by an appropriate wrapper (e.g.,
+# PyArray) rather than copying to a Julia object.
+function _julia_arg(arg)
+    if haskey(PyCall.npy_api, :PyArray_Type) &&
+            pyisinstance(arg, PyCall.npy_api[:PyArray_Type])
+        return convert(PyArray, arg)
+    else
+        return convert(PyAny, arg)
+    end
+end
+
 function _pyjlwrap_call(f, args_::PyPtr, kw_::PyPtr)
     args = PyObject(args_) # don't need pyincref because of finally clause below
     try

test/runtests.jl

@@ -151,6 +151,13 @@ const PyInt = pyversion < v"3" ? Int : Clonglong
         @test x == ["bar"]
     end
 
+    py"""
+    def apply(f, *args):
+        f(*args)
+        return args
+    """
+    @test py"apply"(fill!, zeros(3), 10)[1] == [10, 10, 10]
+
     @test roundtripeq(Dates.Date(2012,3,4))
     @test roundtripeq(Dates.DateTime(2012,3,4, 7,8,9,11))
     @test roundtripeq(Dates.Millisecond(typemax(Int32)))