擅长:python、mysql、java
<p>假设秩序很重要</p>
<pre><code>>>> a = [['Rostock', 'Lubeck'], ['Rostock', 'Hamburg'], ['Rostock', 'Bremen'], ['Rostock', 'Hannover']]
>>> from collections import OrderedDict
>>> list(OrderedDict.fromkeys(y for x in a for y in x))
['Rostock', 'Lubeck', 'Hamburg', 'Bremen', 'Hannover']
</code></pre>
<p>或等效地:</p>
<pre><code>>>> from itertools import chain
>>> list(OrderedDict.fromkeys(chain.from_iterable(a)))
</code></pre>