Is there any way you can make an entry box in tkinter wait for input? (in Python 3)

First of all, 'operation' is called a function, not a method. I recommend you to search about what's the difference at Google.

You don't need Tkinter to wait for Entry. You can check it at the function code. For example check if an entry exists if not then return nothing.

For example:

if not ans.get():
    return

^^^ The example checks if an entry exists, if not it'll return None and stop the function from throwing an error. If you want you can read about try, except as well.

You shouldn't be arbitrarily waiting for input using things like sleep, and attempting to read another value inside of your operation function seems like the wrong logical approach. You can avoid needing to wait on input altogether if you take advantage of the event-driven nature of tkinter controls and abstract your code a bit.

This is a very simple solution based on your original program but modified to store operands and operators in an array before evaluating them in order. There may be a few edge cases where this fails if the user inputs an invalid order of operations, but I tried to accommodate for the obvious cases.

The notable difference is this code isn't trying to evaluate anything within the operation routine. It instead stores the operands and operators until = is entered, which is when evaluation takes place.

import tkinter as tk

root = tk.Tk()
root.title('Calculator')
ans = tk.Entry(root, borderwidth=4, width=40)
ans.grid(row=0, column=0, columnspan=4, padx=10, pady=10)

data = []
tmpnum = None

def typeNum(number):
    global tmpnum
    current = ans.get()
    ans.delete(0, tk.END)
    ans.insert(0, str(current) + str(number))
    tmpnum = int(str(current) + str(number))

def eq():
    global tmpnum
    global data
    if tmpnum:
        data.append(tmpnum)
    print("DEBUG")
    print(data)

    # Evaluate
    if len(data) < 3:
        print("ERROR: incomplete equation")
        data.clear()
        return

    firstnum = data.pop(0)
    operator = data.pop(0)
    secondnum = data.pop(0)
    data.clear()

    if operator == "+":
        answer = firstnum + secondnum
    elif operator == "-":
        answer = firstnum - secondnum
    elif operator == "*":
        answer = firstnum * secondnum
    elif operator == "/":
        answer = firstnum / secondnum

    ans.delete(0, tk.END)
    ans.insert(0, str(answer))
    tmpnum = answer # Store result in case you want to use it for next operation

def operation(op):
    global tmpnum
    global data
    ans.delete(0, tk.END)
    if tmpnum:
        data.append(tmpnum)
        tmpnum = None
        data.append(op)

def clearAll():
    global data
    ans.delete(0, tk.END)
    data.clear()



button1 = tk.Button(root, text='1', padx=40, pady=20, command=lambda: typeNum(1))
button2 = tk.Button(root, text='2', padx=40, pady=20, command=lambda: typeNum(2))
button3 = tk.Button(root, text='3', padx=40, pady=20, command=lambda: typeNum(3))
button4 = tk.Button(root, text='4', padx=40, pady=20, command=lambda: typeNum(4))
button5 = tk.Button(root, text='5', padx=40, pady=20, command=lambda: typeNum(5))
button6 = tk.Button(root, text='6', padx=40, pady=20, command=lambda: typeNum(6))
button7 = tk.Button(root, text='7', padx=40, pady=20, command=lambda: typeNum(7))
button8 = tk.Button(root, text='8', padx=40, pady=20, command=lambda: typeNum(8))
button9 = tk.Button(root, text='9', padx=40, pady=20, command=lambda: typeNum(9))

button0 = tk.Button(root, text='0', padx=40, pady=20, command=lambda: typeNum(0))
equals = tk.Button(root, text='=', padx=40, pady=20, command=eq)
clear = tk.Button(root, text='CLEAR', padx=23, pady=20, command=clearAll)

add = tk.Button(root, text='+', padx=30, pady=20, command=lambda: operation('+'))
sub = tk.Button(root, text='-', padx=30, pady=20, command=lambda: operation('-'))
mult = tk.Button(root, text='x', padx=30, pady=20, command=lambda: operation('*'))
div = tk.Button(root, text='÷', padx=30, pady=20, command=lambda: operation('/'))

button1.grid(row=1, column=0)
button2.grid(row=1, column=1)
button3.grid(row=1, column=2)

button4.grid(row=2, column=0)
button5.grid(row=2, column=1)
button6.grid(row=2, column=2)

button7.grid(row=3, column=0)
button8.grid(row=3, column=1)
button9.grid(row=3, column=2)

button0.grid(row=4, column=0)
equals.grid(row=4, column=1)
clear.grid(row=4, column=2)

add.grid(row=1, column=3)
sub.grid(row=2, column=3)
mult.grid(row=3, column=3)
div.grid(row=4, column=3)

root.mainloop()

I think your solution would also be fine if it didn't mess up the GUI. Time.sleep() function completely stops the code including the GUI so I recommend using a threading with tkinter.

https://www.youtube.com/watch?v=FwKQwx91NAM

This video will help your problem with messing up with the GUI.