def getFloatFromUser(message):
    """
    Obtains positive real number from user.
        
    Arguments:
    message -- the message that is printed for the user, describing what is expected
    
    Returns:
    var -- a positive real number that the user entered
    """
    
    var = None # initialize the variable we return
    
    # try to get input from user until it works
    while var is None:
        var = input(message)
        try:
            var = float(var)
            if var < 0.0: raise ValueError('Must be positive!')
        except: # if var is not float or positive, it comes here
            print("\t Please, enter a positive real number...")
            var = None
            
    return var