import tkinter as tk

coords = [[100, 100], [300, 300]]


root = tk.Tk()
canvas = tk.Canvas(width=400,
                   height=400,
                   background="bisque")
canvas.pack(fill="both", expand=True)
line = canvas.create_line(coords)
coords[1] = [200, 200]
canvas.coords(line, coords)  # line with error

root.mainloop()