help me~!about base64

[ylj798 at gmail.com]

my code：
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import base64
def deflashget(st):
     if st.startswith('Flashget://'):
         return base64.decodestring(st[len('Flashget://'):])[10:-10]
     elif st.startswith('http://') or st.startswith('ftp://'):
         return 'Flashget://' + base64.encodestring('[FLASHGET]' + st
+'[FLASHGET]').replace('\n', '')

st='Flashget://
W0ZMQVNIR0VUXWh0dHA6Ly9kb3duLnJub3ZlbC5jb20vYm9va3R4dC8zLzEzNjgyLzEzNjgyLnppcFtGTEFTSEdFVF0=&1064'
print deflashget(st)
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it's run ,Eric gave me error,the error is "'module' object has no
attribute 'decodestring'",
what can I do? who can help me?