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import tkinter as t
import tkinter.font as f

class App:
    def __init__(self):
        root=t.Tk()

        self.customFont=f.Font(family="Helvetica", size = 12)

        buttonframe = t.Frame()
        label=t.Label(root, text="Hello, World!",f=self.customFont)
        buttonframe.pack()
        label.pack()

        bigger = t.Button(root, text="폰트를 크게", command=self.BigFont)
        smaller = t.Button(root, text="폰트를 작게", command=self.SmallFont)
        bigger.pack()
        smaller.pack()
        root.mainloop()
    def BigFont(self):
        size = self.customFont['size']
        self.customFont.configure(size=size+10)

    def SmallFont(self):
        size = self.customFont['size']
        self.customFont.configure(size=size-10)

app=App()