Compare two lists from sql in python and show result using

I’m having a question on python. I’m trying to compare two dataframes and check which elements are different and insert them into another dataframe. So here are my dataframes. df1:

PN      Stock        WHS      Cost
1111     1           VLN       0.2
1111     2           VLN       0.2
1115     1           KNS       0.5 


    PN      Stock        WHS      Cost    Time
   1111        1         VLN       0.2     15:00
   1111        3         VLN       0.2     16:00

So the idea is to add to df1 the data from df2 that is not yet in df1; line 2 in df2 does not exist in df1 so I want to insert it.
How should i write code to find not existing line so that I could insert it?
I have tried:

   for index, row in df1.iterrows():
        if df2[(df2['PN']==row['PN']) & (df2['Stock'] ==row['Stock']) & (df2['Whs'] = row['Whs']) & (df2['Cost']==row['Cost'])].empty
              print row['PN']

To check which rows to update but i get basically all rows printed, not the ones that do not match. How can I solve this please? Is it possible to use somehow ‘IN’ function, comparing each df1 line with whole df2???

Source: sql

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