沿轴1使用pandas.concat返回沿轴0的级联

我试图水平连接一对具有相同索引的数据帧,但结果总是垂直连接,其中NaN值插入到每一列中。

dct_l = {'1':'a', '2':'b', '3':'c', '4':'d'}
df_l = pd.DataFrame.from_dict(dct_l, orient='index', columns=['Key'])

dummy = np.zeros((4,3))
index = np.arange(1,5)
columns = ['POW', 'KLA','CSE']
df_e = pd.DataFrame(dummy, index, columns)

print(df_l)

  Key
1   a
2   b
3   c
4   d

print(df_e)

   POW  KLA  CSE
1  0.0  0.0  0.0
2  0.0  0.0  0.0
3  0.0  0.0  0.0
4  0.0  0.0  0.0

pd.concat([df_l, df_e], axis=1)

实际结果

   Key  POW  KLA  CSE
1    a  NaN  NaN  NaN
2    b  NaN  NaN  NaN
3    c  NaN  NaN  NaN
4    d  NaN  NaN  NaN
1  NaN  0.0  0.0  0.0
2  NaN  0.0  0.0  0.0
3  NaN  0.0  0.0  0.0
4  NaN  0.0  0.0  0.0

预期结果

   Key  POW  KLA  CSE
1    a  0.0  0.0  0.0
2    b  0.0  0.0  0.0
3    c  0.0  0.0  0.0
4    d  0.0  0.0  0.0

这里发生了什么事?