title: Pandas: type of file to save to contain dtypes
body: <p>I'm working on some <code>datasets</code> contains many <code>DateTime</code> variables. I always save a <code>.csv</code> file after the data cleaning. However, when I load the file to pandas next time, I have to convert <code>dtypes</code> again and it will take a long time. Thus, I wonder if there is a type of file I can save with Pandas to avoid this.</p>