How to remove rows in a Pandas dataframe if the same row exists in another dataframe?

You an use merge with parameter indicator and outer join, query for filtering and then remove helper column with drop:

DataFrames are joined on all columns, so on parameter can be omit.

print (pd.merge(a,b, indicator=True, how='outer')
         .query('_merge=="left_only"')
         .drop('_merge', axis=1))
   0   1
0  1  10
2  3  30