Calcular ángulo

import turtle

def check_if_valid(var):
    while True:
        if var.isdigit():
            break
        else:
            var = input('Enter a valid number ->')


def get_x_and_y():
    x = input('\'x\' coordinate -> ')
    check_if_valid(x)
    y = input('\'y\' coordinate -> ')
    check_if_valid(y)
    return [int(x),int(y)]

print('This program will read in 2 points, and draw 2 lines. \n\
Then it will calculate the acute (smaller) angle \n\
between the 2 lines you draw.')

# get coordinates


print('1st point')
point1 = get_x_and_y()
print('2nd point')
point2 = get_x_and_y()

# calculates the acute angle

up = point2[1] - point1[1]
down = point2[0] - point1[0]
m = up / down
'''Aquí el problema! ¿Cómo obtener 2 puntos por cada línea?'''

# start drawing
turtle.title('Angle Calculator')

#multiplicados por 4 para hacer las líneas más grandes.
turtle.goto(point1[0] * 4, point1[1] * 4) #goes to the first point
turtle.goto(point2[0] * 4, point1[1] * 4) # goes to the second point

turtle.done()