title: Pandas square bracket chaining vs double indexes in single brackets
body: <p>Considering I have the following dataframe</p>
  <pre><code>import pandas as pd
  purchase_1 = pd.Series({'Name': 'Chris',
                          'Item Purchased': 'Dog Food',
                          'Cost': 22.50})
  purchase_2 = pd.Series({'Name': 'Kevyn',
                          'Item Purchased': 'Kitty Litter',
                          'Cost': 2.50})
  purchase_3 = pd.Series({'Name': 'Vinod',
                          'Item Purchased': 'Bird Seed',
                          'Cost': 5.00})
  df = pd.DataFrame([purchase_1, purchase_2, purchase_3], index=['Store 1', 'Store 1', 'Store 2'])
  </code></pre>
  <p>what is the difference between <code>df_slice = df.loc['Store 1', 'Cost']</code> and <code>df_slice = df['Cost']['Store 1']</code>? When I change the value of these slices, the original dataframe is modified in both cases. Although when I try to change the value of the slice from the first option, it raises an error when ran in Jupyter Notebook: <strong>SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame</strong>.</p>