cmp是Python2.x自帶的比較函數，無需import模塊。官方手冊說明：

cmp(x, y)

Compare the two objects x and y and return an integer according to theoutcome.  The return value is negative if x < y, zero if x == y andstrictly positive if x > y.

如下所示：

python3.x則取消了這個函數，以下是官方說明：

The cmp() function should be treated as gone, and the __cmp__() special method is no longer supported. Use __lt__() for sorting, __eq__() with __hash__(), and other rich comparisons as needed. (If you really need the cmp() functionality, you could use the expression (a > b) - (a < b) as the equivalent for cmp(a, b).)大意就是cmp()函數已經“離開”了，如果你真的需要cmp()函數，你可以用表達式(a > b) - (a < b)代替cmp(a,b)

比如你一開始用的:
import modulename
如果修改的話，要這樣：
reload(modulename)