new_contents: 
  
  
  def adjusted_percent_change(s, lag=1, epsilon=0.1, center=0):
      """ Where s is a pandas timeseries, it calculates the percent
          change for a given lag interval. Uses epsilon to prevent
          division by zero problems, and infinities. 
      """
      out = (s+epsilon)/(s.shift(lag)+epsilon)
      if center == 1:
          return out
      elif center == 0:
          return out - 1
      else:
          assert False, "`center` must be 1 or 0"
  
subject: Add adjusted percentage change