Simple Calculator

import tkinter as tk

calculation = ""

def add_to_calculation(symbol):
    global calculation #global key word makes calculation available across the program 
    calculation += str(symbol)                    # and not just in the function
    text_result.delete(1.0, "end")
    text_result.insert(1.0, calculation)
    
def evaluate_calculation():
    global calculation
    try:
        
        calculation = str(eval(calculation))
        text_result.delete(1.0, 'end')
        text_result.insert(1.0, calculation)
    except:
        clear_field()
        text_result.insert(1.0, "Error")


def clear_field():
    global calculation
    calculation = ''
    text_result.delete(1.0, "end")
    

root = tk.Tk() # the display field
root.geometry("300x275") #size of the display field

text_result = tk.Text(root, height=2, width=16, font=("Arial", 24)) #field that returns the calculation
text_result.grid(columnspan=5)
btn_1 = tk.Button(root, text="1", command= lambda: add_to_calculation(1), width="5", font=("Arial", 14))
btn_1.grid(row=2, column=1)
btn_2 = tk.Button(root, text="2", command= lambda: add_to_calculation(2), width="5", font=("Arial", 14))
btn_2.grid(row=2, column=2)
btn_3 = tk.Button(root, text="3", command= lambda: add_to_calculation(3), width="5", font=("Arial", 14))
btn_3.grid(row=2, column=3)
btn_4 = tk.Button(root, text="4", command= lambda: add_to_calculation(4), width="5", font=("Arial", 14))
btn_4.grid(row=3, column=1)
btn_5 = tk.Button(root, text="5", command= lambda: add_to_calculation(5), width="5", font=("Arial", 14))
btn_5.grid(row=3, column=2)
btn_6 = tk.Button(root, text="6", command= lambda: add_to_calculation(6), width="5", font=("Arial", 14))
btn_6.grid(row=3, column=3)
btn_7 = tk.Button(root, text="7", command= lambda: add_to_calculation(7), width="5", font=("Arial", 14))
btn_7.grid(row=4, column=1)
btn_8 = tk.Button(root, text="8", command= lambda: add_to_calculation(8), width="5", font=("Arial", 14))
btn_8.grid(row=4, column=2)
btn_9 = tk.Button(root, text="9", command= lambda: add_to_calculation(9), width="5", font=("Arial", 14))
btn_9.grid(row=4, column=3)
btn_0 = tk.Button(root, text="0", command= lambda: add_to_calculation(0), width="5", font=("Arial", 14))
btn_0.grid(row=5, column=2)
btn_plus = tk.Button(root, text="+", command= lambda: add_to_calculation("+"), width="5", font=("Arial", 14))
btn_plus.grid(row=2, column=4)
btn_minus = tk.Button(root, text="-", command= lambda: add_to_calculation("-"), width="5", font=("Arial", 14))
btn_minus.grid(row=3, column=4)
btn_multiply = tk.Button(root, text="*", command= lambda: add_to_calculation("*"), width="5", font=("Arial", 14))
btn_multiply.grid(row=4, column=4)
btn_divide = tk.Button(root, text="/", command= lambda: add_to_calculation("/"), width="5", font=("Arial", 14))
btn_divide.grid(row=5, column=4)
btn_equal = tk.Button(root, text="=", command= evaluate_calculation, width="5", font=("Arial", 14))
btn_equal.grid(row=6, column=4)
btn_open = tk.Button(root, text="(", command= lambda: add_to_calculation("("), width="5", font=("Arial", 14))
btn_open.grid(row=5, column=1)
btn_close = tk.Button(root, text=")", command= lambda: add_to_calculation(")"), width="5", font=("Arial", 14))
btn_close.grid(row=5, column=3)
btn_clear = tk.Button(root, text="clear", command= clear_field, width="5", font=("Arial", 14))
btn_clear.grid(row=6, column=1, columnspan=3)
root.mainloop()