How to get html elements with multiple css classes

The expression you're looking for is:

//div[contains(@class, 'class1') and contains(@class, 'class2')]

I highly suggest XPath visualizer, which can help you debug xpath expressions easily. It can be found here:

http://xpathvisualizer.codeplex.com/

According to this answer, which explains why it is important to make sure substrings of the class name that one is looking for are not included, the correct answer should be:

//div[contains(concat(' ', normalize-space(@class), ' '), ' class1 ')
    and contains(concat(' ', normalize-space(@class), ' '), ' class2 ')]

There's a useful python package called cssselect.

from cssselect import CSSSelector CSSSelector('div.gallery').path

Generates a usable XPath:

descendant-or-self::div[@class and contains(concat(' ', normalize-space(@class), ' '), ' gallery ')]

It's very similar to Flynn1179's answer.