Loading a DataFrame:
	
	1) from a local CSV file:
	   df = pd.read_csv('WHO.csv', delimiter = ',', index_col=0)
	   
	2) read a CSV file from a URL:
	    URL = "http://www.jre-training.com/Python/notes/population.csv" 
	    master_df = pd.read_csv(URL)
	    
	3) read JSON from REST API:
	   df=pd.read_json('https://api.github.com/users/mralexgray/repos')
 
	4) read from a SQL query:
	    df = pd.read_sql_query("SELECT * from ORDERS", connection)