# pytds.extensions – Extensions to the DB API

## Isolation level constants

`pytds.extensions.``ISOLATION_LEVEL_READ_UNCOMMITTED`

  Transaction can read uncommitted data

`pytds.extensions.``ISOLATION_LEVEL_READ_COMMITTED`

  Transaction can read only committed data, will block on attempt to read modified uncommitted data

`pytds.extensions.``ISOLATION_LEVEL_REPEATABLE_READ`

  Transaction will place lock on read records, other transactions will block trying to modify such records

`pytds.extensions.``ISOLATION_LEVEL_SERIALIZABLE`

  Transaction will lock tables to prevent other transactions from inserting new data that would match selected recordsets

`pytds.extensions.``ISOLATION_LEVEL_SNAPSHOT`

  Allows non-blocking consistent reads on a snapshot for transaction without blocking other transactions changes