擅长:python、mysql、java
<p>来自<a href="https://docs.python.org/3/library/stdtypes.html#set-types-set-frozenset" rel="noreferrer">the official docs</a></p>
<blockquote>
<p>The frozenset type is immutable and hashable — its contents cannot be altered after it is created; <strong>it can therefore be used as a dictionary key</strong> or as an element of another set.</p>
</blockquote>
<p>(重点是我的)</p>