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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def get_by_signature(user_id, app_id):
        '''
        Get the collection.
        '''
        try:
            return TabCollect.get(
                (TabCollect.user_id == user_id) &
                (TabCollect.post_id == app_id)
            )
        except:
            return None