def numerical(df):
    """ Extract names of numerical column
    
    This function accepts a dataframe and returns numerical list,
    containing the names of numerical columns(numerical_var).
        
    Keyword arguments:
    df - Pandas dataframe from which the columns name will be extracted
    
    Returns:
    numerical_var - List of numerical features
    """
    numerical_var = df.select_dtypes(include = 'number')
    return numerical_var.columns