hacer con python 2 hojas de un excel

def read_excel(filename=None):
    #filename = './HW1_data.xlsx'
    df = pd.read_excel(filename).dropna()
    df.columns = ['country', 'population', 'area', 'density']
    return df

df = read_excel()
df2 = read_excel('./HW1_data2.xlsx')