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copied!<p><code>.decode('base64')</code> can be called only on a string that's encoded as "base-64, in order to retrieve the byte sequence that was there encoded. Presumably that byte sequence, in the example you bring, was zlib-compressed, and so the <code>.decode('zlib')</code> part decompresses it.</p> <p>Now, for your case:</p> <pre><code>>>> 'dsss'.decode('base64') 'v\xcb,' </code></pre> <p>But <code>'v\xcv,'</code> is not a zlib-compressed string! And so of course you cannot ask zlib to "decompress" it. Fortunately <code>zlib</code> recognizes the fact (that <code>'v\xcv,'</code> could not possibly have been produced by applying any of the compression algorithms <code>zlib</code> knows about to any input whatsoever) and so gives you a helpful error message (instead of a random-ish string of bytes, which you might well have gotten if you had randomly supplied a different but equally crazy input string!-)</p> <p><strong>Edit</strong>: the error in</p> <pre><code>a.encode('base64') print a a.decode('base64')#error </code></pre> <p>is obviously due to the fact that <strong>strings are immutable</strong>: just calling <code>a.encode</code> (or any other method) does <strong>not</strong> alter <code>a</code>, it produces a new string object (and here you're just printing it).</p> <p>In the next snippet, the error is only in the OP's mind:</p> <pre><code>>>> a='dsss' >>> a=a.encode('zlib') >>> print a x?K)..F? >>> a=a.decode('zlib') >>> print a#why can't print 'dsss' dsss >>> </code></pre> <p>that "why can't print" question is truly peculiar, applied to code that <strong>does</strong> print 'dsss'. Finally, </p> <blockquote> <p>i think the 'print a' encode the a with 'uhf-8'.</p> </blockquote> <p>You think wrongly: there's no such thing as "uhf-8" (you mean "utf-8" maybe?), and anyway <code>print a</code> does <strong>not</strong> alter <code>a</code>, any more than just calling <code>a.encode</code> does.</p>

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