>>> L = [1,10,56,23,897,56,1000]
>>> L.remove(56)
>>> L
[1, 10, 23, 897, 56, 1000]
>>> L.remove(100000)
Traceback (most recent call last):
  File "<pyshell#165>", line 1, in <module>
    L.remove(100000)
ValueError: list.remove(x): x not in list