I just made an app using python and tkinter widgets. 
 There are Labels, Frames, Buttons, etc in the Tk and Toplevel widgets.
However, it includes thousands of codes and its really annoying to resize every widgets when I support multiple resolutions.
Is there any way to expand the resolution ratio for existing Tkinter Tk() and Toplevel() widget and their child widgets? (zooming-in)
 If not, what would be the best approach to support multiple resolutions of a python app with the same ratio?
 Any help would be much appreciated, sorry for bad English.
Can't comment so I add a short tip to the detailed Ethan answer. You can design most of the GUIs in tkinter with either pack,  grid or a combination of both (by placing frames on a window with one of them, and using either grid or pack inside of each frame, to "place" the widgets). You can tune the configurations for proper location and size when the window resizes. Keep placer use for special cases (like overlaying some widget on the top of others)
Python - is there any way to expand the resolution ratio for existing Tkinter Tk() and Toplevel() widget? (zooming-in)