Based on this answer here, you can try pd.concat
method:
pd.concat([A,B]).drop_duplicates(keep=False)['column1'].unique().tolist()
Output:
# if you just want to see the differences between the dataframe
>>> pd.concat([A,B]).drop_duplicates(keep=False)
column1 column2
1 def 2
1 def 1
# if you just want to see the differences and with only 'column1'
>>> pd.concat([A,B]).drop_duplicates(keep=False)['column1']
1 def
1 def
Name: column1, dtype: object
# if you want unique values in the column1 as a numpy array after taking the differences
>>> pd.concat([A,B]).drop_duplicates(keep=False)['column1'].unique()
array(['def'], dtype=object)
# if you want unique values in the column1 as a list after taking the differences
>>> pd.concat([A,B]).drop_duplicates(keep=False)['column1'].unique().tolist()
['def']