如何重命名dataframe的特定列？

df1 = pd.DataFrame(data=np.array([[18,50],[19,51],[20,55]]),index=['man1','man2','man3'],columns=['age','weight'])
print(df1)
# 修改列名
print("\nchange columns :\n")
#方法1
df1.rename(columns={'weight':'stress'})
#方法2
df1.columns.values[1] = 'stress'
print(df1)

#>	      age  weight
	man1   18      50
	man2   19      51
	man3   20      55
	
	change columns :
	
	      age  stress
	man1   18      50
	man2   19      51
	man3   20      55