[::-1]

In [21]: str1=''

In [22]: for i in range(10):
    ...:     str1=str1+str(i)
    ...:

In [23]: str1
Out[23]: '0123456789'

In [24]: str1[0:10]
Out[24]: '0123456789'

In [25]: str1[:10]
Out[25]: '0123456789'

In [27]: str1[:10]
Out[27]: '0123456789'

In [28]: str1[:]
Out[28]: '0123456789'

In [29]: str1[0:5:2]
Out[29]: '024'

In [31]: str1[::2]
Out[31]: '02468'

In [32]: str1[::-1]
Out[32]: '9876543210'

In [33]: str1[::-2]
Out[33]: '97531'