title: how to slice a pandas data frame more elegantly
body: <p>i'm wondering if there is a better way to slice a data frame with different criteria for the same variable.</p>
  <p>actually i'm looking at this example:
  <code>df_european_union = df[(df['Country'] == 'Austria')|(df['Country'] == 'Belgium')|(df['Country'] == 'Bulgaria')...</code></p>
  <p>this works just fine but i don't think it's close to best practice.</p>
  <p>already tried approaches like:
  <code>df_european_union = df[(df['Country'] == ['Austria','Belgium', ... ]]</code></p>
  <p>or
  <code>eu = ['Austria','Belgium','Bulgaria',...] df_european_union = df[(df['Country'] == eu]</code></p>