Is it possible to call a class but without a new instance created?

[Peter Otten]

Jach Fong wrote:

> Is it possible to call a class but without a new instance created?

Yes, this is possible in Python, by writing a custom __new__ method. An 
extreme example:

>>> class Three:
...     def __new__(*args): return 3
... 
>>> a = Three()
>>> b = Three()
>>> a
3
>>> b
3
>>> a is b
True

But this is not what is done with the tkinter Font class. Most tkinter 
classes refer to a tcl/tk object and so does Font.

import tkinter as tk
from tkinter.font import Font

root = tk.Tk()

a = Font(root, name="foo", size=10, exists=False)

label = tk.Label(root, text="hello", font=a)
label.pack()

def update_foo():
    b = Font(root, name="foo", size=20, exists=True)
    # two distinct Font objects referring to the same underlying tcl font.
    assert a is not b


button = tk.Button(root, text="update foo font to 20pt", command=update_foo)
button.pack()

root.mainloop()

Here the b = Font(...) creates another wrapper for the "foo" font and 
updates its size in the process so that the label's appearance is updated, 
too.