Is there a way to iterate all sub-files inside a .blend file's directories?

So my end goal is to link all brushes from one blend file into another via a script. I know I can link one brush by using the following:

bpy.ops.wm.link(directory="F:/Blender/Scenes/brushes.blend/Brush", filename="CustomBrushForImport")

I also know I can iterate through a folder of files by using the following in python (currently using print so I can visualize what's happening in console)

for filename in os.listdir(testDirectory):
       print (filename)

AFAIK (from what I've tried), I cannot use os.listdir to access anything inside the .blend file (i.e. F:/Blender/Scenes/brushes.blend/Brush), but I don't know of any other functions that operate similarly but for this unique sub-directory. Is there some way to do the same method, or should I just look at creating a list of brushes instead and checking for those brushes inside the .blend file?

Thanks!