I have this pandas dataframe:

    Column1   Column2    Column3
1     A                     C
2     A         D   
3     B

If the is a "D" in my column2 i want to duplicate the row with is values and reset the index like this :

    Column1  Column2    Column3
1     A                    C
2     A         D   
3     A         D   
4     B

How do I do this in pandas?

>Solution :

First test if duplicated columns names, if necessary deduplicate them:

print (df.columns[df.columns.duplicated(keep=False)])

Then join filtered rows with concat and sort indices:

df = df.reset_index(drop=True)

df = (pd.concat([df, df[df['Column2'].eq('D')]])
        .sort_index(kind='stable', ignore_index=True)
        .rename(lambda x: x+1))
print (df)
  Column1 Column2 Column3
1       A     NaN       C
2       A       D     NaN
3       A       D     NaN
4       B     NaN     NaN