How to get active_texture.name
via python? Or get active_texture[ID]
?
(I mean a texture in active slot)
In this case, you can reference it from the brush it is applied to:
bpy.data.brushes['NameOfBrush'].texture
Or use the active brush (if the context is sculpt mode, texture mode, etc.):
bpy.context.brush.texture
Or:
bpy.context.sculpt.brush.texture
https://www.blender.org/api/blender_python_api_current/info_api_reference.html#indirect-data-access