>>> def rev(X):
...     L = list(X)
...     L.reverse()
...     return L
...
>>> rev('spam')
['m', 'a', 'p', 's']


>>> def rev(X):
...     res = X[:0]
...     for i in range(len(X)):
...         res = X[i:i+1] + res
...     return res
...
>>> rev('spam')
'maps'
>>> rev([1, 2, 3])
[3, 2, 1]
>>> rev(('a', 'b', 'c'))
('c', 'b', 'a')