title: Python: pandas dataframe condition for slice of a dataframe
body: <p>I want to change the content in a slice of the pandas dataframe column that has 'ABC' ONLY in the column if the condition is fulfill.
  I try the code as below but it return this error</p>
  
  <blockquote>
  <pre><code>A value is trying to be set on a copy of a slice from a DataFrame.Try using .loc[row_indexer,col_indexer] = value instead
  </code></pre>
  </blockquote>
  
  <pre><code> print df
  
     Item  Price  Quantity
  0  ABC    10     30
  1  ABB    20     50 
  2  ABC    37     89
  3  ABG    5      78
  
  con1 = df['Price']&gt;10
  con2 = df['Quantity']&gt;20
  df[df['Item']=='ABC'].loc[con1 &amp; con2,'Item'] = 'ABCD'
  
  Output that I want
  
     Item  Price  Quantity
  0  ABC    10     30
  1  ABB    20     50 
  2  ABCD   37     89
  3  ABG    5      78
  </code></pre>