Drop duplicate row if column is null

drop_duplicate_if_null.py

>>> df1
   name  flag
0     1     1
1     2     1
2     3     1
3     4     1
>>> df2
   name  flag
0     3   NaN
1     4   NaN
>>>
>>> df = df1.append(df2)
<stdin>:1: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
>>>
>>> df
   name  flag
0     1   1.0
1     2   1.0
2     3   1.0
3     4   1.0
0     3   NaN
1     4   NaN
>>>
>>>
>>> _flags = df.flag.notna()
>>>
>>> _names = ~df.name.duplicated()
>>>
>>> df[_flags & _names]
   name  flag
0     1   1.0
1     2   1.0
2     3   1.0
3     4   1.0