How to modify the default font in Tkinter?

Tkinter has several built-in fonts — TkDefaultFont, TkTextFont, TkFixedFont, etc. These are all what are called “named fonts”. They are remarkably powerful — change one of these and all widgets that use them will change as well.

To change one of these fonts, get a handle to it and then use the configure method to change. For example, to change the size of TkDefaultFont to 48 you would do this:

default_font = tkFont.nametofont("TkDefaultFont")

That’s it. You don’t have to do anything else — everything that uses TkDefaultFont will instantly notice the change.

In your question you imply you want TkDefaultFont font to be used by everything. To do that you can use option_add as you’ve shown:

root.option_add("*Font", default_font)

Note, however, that option_add only affects widgets created after you’ve called option_add, so you need to do it before creating any other widgets.

Also note that you can give the font name to option_add if you don’t want to bother with getting the font instance first (ie: root.option_add("*Font", "TkDefaultFont")).

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