title: Applying function with multiple arguments to create a new pandas column
body: <p>I want to create a new column in a <code>pandas</code> data frame by applying a function to two existing columns. Following this <a href="https://stackoverflow.com/a/14603893/2327821">answer</a> I've been able to create a new column when I only need one column as an argument:</p>
  
  <pre><code>import pandas as pd
  df = pd.DataFrame({"A": [10,20,30], "B": [20, 30, 10]})
  
  def fx(x):
      return x * x
  
  print(df)
  df['newcolumn'] = df.A.apply(fx)
  print(df)
  </code></pre>
  
  <p>However, I cannot figure out how to do the same thing when the function requires multiple arguments. For example, how do I create a new column by passing column A and column B to the function below?</p>
  
  <pre><code>def fxy(x, y):
      return x * y
  </code></pre>