python中如何给列表排序

>>> a = ["dd","cc","aa","bb"]
>>> a
['dd', 'cc', 'aa', 'bb']
>>> b = sorted(a)  ## 排序并赋值给b
>>> b
['aa', 'bb', 'cc', 'dd']
>>> a
['dd', 'cc', 'aa', 'bb']
>>> c = sorted(a,reverse = True)  ## 逆向排序并赋值给c
>>> c
['dd', 'cc', 'bb', 'aa']
>>> a
['dd', 'cc', 'aa', 'bb']
>>> a.sort()   ## 直接在源列表排序
>>> a
['aa', 'bb', 'cc', 'dd']
>>> a.sort(reverse = True)  ## 直接在源列表逆向排序
>>> a
['dd', 'cc', 'bb', 'aa']