df=pd.DataFrame(np.array([1,2,3,4,np.nan,6,7,8,9,10,np.nan]).reshape(-1,11))
df.fillna(method='ffill',axis=1)

0   1   2   3   4   5   6   7   8   9   10
0   1.0 2.0 3.0 4.0 4.0 6.0 7.0 8.0 9.0 10.0    10.0

df.fillna(method='bfill',axis=1)
    0   1   2   3   4   5   6   7   8   9   10
0   1.0 2.0 3.0 4.0 6.0 6.0 7.0 8.0 9.0 10.0    NaN