How to change font and size of buttons and frame in tkinter using python?

tkdocs tutorial recommends using named fonts and styles if you want to tweak the appearences:

import random
try:
    import tkinter as Tk
    import tkinter.ttk as ttk
    import tkinter.font as font
except ImportError: # Python 2
    import Tkinter as Tk
    import ttk
    import tkFont as font

def change_font_family(query, named_font):
    named_font.configure(family=random.choice(font.families()))

root = parent = Tk.Tk()
root.title("Change font demo")

# standard named font (everything that uses it will change)
font.nametofont('TkDefaultFont').configure(size=5) # tiny

# you can use your own font
MyFont = font.Font(weight='bold')

query = Tk.StringVar()
ttk.Entry(parent, textvariable=query, font=MyFont).grid() # set font directly
ttk.Button(parent, text='Change Font Family',  style='TButton', # or use style
           command=lambda: change_font_family(query, MyFont)).grid()
query.set("The quick brown fox...")

# change font that widgets with 'TButton' style use
root.after(3000, lambda: ttk.Style().configure('TButton', font=MyFont))
# change font size for everything that uses MyFont
root.after(5000, lambda: MyFont.configure(size=48)) # in 5 seconds
root.mainloop()

UPDATE: The New Mexico Tech tkinter website has been archived on GitHub.

First the best reference for Tkinter is this New Mexico Tech website. In the toc you will find a section on fonts, and in the section on Button widgets you'll find the option font.

you must have a Tkinter object to create a font

Python-2

Support for Python-2 has officially ended as of Jan 1, 2020

from Tkinter import *  # Note: UPPER case "T" in Tkinter
import tkFont
root = Tk()

Python-3

Python-3 Tk wrappers differ from Python-2

from tkinter import *  # Note: lower case "t" in tkinter
from tkinter import font as tkFont  # for convenience
root = Tk()

create a font like the example from New Mexico Tech website

helv36 = tkFont.Font(family='Helvetica', size=36, weight='bold')
# you don't have to use Helvetica or bold, this is just an example

(Note: recall for Python-3 font was imported as tkFont for convenience)

now you can set the font for button created from Button in the original post

button['font'] = helv36

The size of the button will depend on your geometry manager, EG: grid or pack. Only the grid method is covered in the layouts section by New Mexico Tech site, but effbot.org is also a great reference and he covers pack pretty well.

try:  # Python-2
    from Tkinter import *
    import tkFont
except ImportError:  # Python-3
    from tkinter import *
    from tkinter import font as tkFont
# using grid
# +------+-------------+
# | btn1 |    btn2     |
# +------+------+------+
# | btn3 | btn3 | btn4 |
# +-------------+------+
root = Tk()
# tkFont.BOLD == 'bold'
helv36 = tkFont.Font(family='Helvetica', size=36, weight=tkFont.BOLD)
btn1 = Button(text='btn1', font=helv36)
btn2 = Button(text='btn2', font=helv36)
btn3 = Button(text='btn3', font=helv36)
btn4 = Button(text='btn4', font=helv36)
btn5 = Button(text='btn5', font=helv36)
root.rowconfigure((0,1), weight=1)  # make buttons stretch when
root.columnconfigure((0,2), weight=1)  # when window is resized
btn1.grid(row=0, column=0, columnspan=1, sticky='EWNS')
btn2.grid(row=0, column=1, columnspan=2, sticky='EWNS')
btn3.grid(row=1, column=0, columnspan=1, sticky='EWNS')
btn4.grid(row=1, column=1, columnspan=1, sticky='EWNS')
btn5.grid(row=1, column=2, columnspan=1, sticky='EWNS')

Also try ttk.