import tkinter as tk

# --- functions ---

def other_function(value):
    print('Other Function:', value)

def on_click():
    print('Entry:', entry.get())
    other_function( entry.get() )

# --- main ---

root = tk.Tk()

entry = tk.Entry(root)
entry.pack()

button = tk.Button(root, text='OK', command=on_click)
button.pack()

root.mainloop()

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