import math
def main():
    print("Please enter (x,y) of the two points in turn:")
    x1,y1=eval(input("Point1:(x,y)="))
    x2, y2 = eval(input("Point2:(x,y)="))
def square(x):
    return x*x
def distance (x1,y1,x2,y2):
    dist=math.sqrt(square(x1-x2)+square(y1-y2))
    return dist
    print("The distance of two points is :" 'dist')
main()

eval()是将字符串转换为有效的表达式进行计算，得到的是一个值，你这个程序不需eval就可以吧，直接用int()将字符类型数字转换即可，建议百度一下eval()的用法