Partial borders in Python Tkinter
The answer to your question depends on what you mean by "borders". Individual widgets have borders (buttons, etc), and for those you can't change just part of the border.
If instead you're asking about how to layout your widgets so that there are dividing lines between them, you can do this with the padx and pady options of grid and pack. For those you can have different amounts of padding on each edge.
There is no way to this built in to tkinter, but why do you need this behaviour? There is probably a better way to accomplish what you need. See this this resource for more help with your problem.