Can't append a *.blend file: "Nothing indicated"


I try to use bpy.ops.wm.append() to import everything from Objects section of a source *.blend file into my master *.blend file. Here’s my code:

blendfile = "Z:\Source.blend"
section   = "\\Object\\"
bpy.ops.wm.append(directory = blendfile + section)

I get a following error:
Error: 'D:\Source.blend\Object\': nothing indicated

It seems that Blender wants me to specify an object, but I’d like to append everything from Objects section.