text: import pandas as pd
  from matplotlib import pyplot as plt
  
  # read data from file
  def read_column_from_data(file_path, column_name, num_measurements = None):
   
    """
    calculates mean from the data in an csv file
  	Args:
  	file_path(string)
  	num_measurements(int) : 
  	Returns:
  	column_data (panda series)
    """
  
    if num_measurements:
      data = pd.read_csv(file_path, nrows=num_measurements)
    else:
      data = pd.read_csv(file_path)
    column_data = data[column_name]
    return column_data
  
  temperatures = read_column_from_data(file_path = 'temperatures.csv', column_name = 'Air temperature (degC)', num_measurements = 25)
  
  # compute statistics
  mean = temperatures.mean()
  
  # plot results
  plt.plot(temperatures, 'r-')
  plt.axhline(y=mean, color='b', linestyle='--')
  plt.savefig('25.png')
  plt.clf()
  