fillna for a column pandas code example
Example 1: dataframe fillna with 0
df['column'] = df['column'].fillna(0)
Example 2: DataFrame.fillna
>>> df.fillna(0)
A B C D
0 0.0 2.0 0.0 0
1 3.0 4.0 0.0 1
2 0.0 0.0 0.0 5
3 0.0 3.0 0.0 4