>>> from sqlalchemy import exc
>>> dir(exc)
['ArgumentError', 'CircularDependencyError', 'CompileError', 'ConcurrentModificationError', 'DBAPIError', 'DataError', 'DatabaseError', 'DisconnectionError', 'FlushError', 'IdentifierError', 'IntegrityError', 'InterfaceError', 'InternalError', 'InvalidRequestError', 'NoReferenceError', 'NoReferencedColumnError', 'NoReferencedTableError', 'NoSuchColumnError', 'NoSuchTableError', 'NotSupportedError', 'OperationalError', 'ProgrammingError', 'SADeprecationWarning', 'SAPendingDeprecationWarning', 'SAWarning', 'SQLAlchemyError', 'SQLError', 'TimeoutError', 'UnboundExecutionError', 'UnmappedColumnError', '__builtins__', '__doc__', '__file__', '__name__', '__package__']
>>>

from sqlalchemy import exc
db.add(user)
try:
  db.commit()
except exc.SQLAlchemyError:
  pass