擅长:python、mysql、java
<p>这个<a href="https://docs.python.org/2/library/stdtypes.html#str.join" rel="nofollow noreferrer">doc</a>还说:</p>
<blockquote>
<p>A TypeError will be raised if there are any non-string values in
iterable...</p>
</blockquote>
<p>毕竟,<code>Symbol('a')</code>不是一个字符串</p>