1.2.0

Released: September 20, 2019

• [command] [feature] Added new --purge flag to the alembic stamp command, which will
  unconditionally erase the version table before stamping anything. This is
  useful for development where non-existent version identifiers might be left
  within the table. Additionally, alembic.stamp now supports a list of
  revision identifiers, which are intended to allow setting up muliple heads
  at once. Overall handling of version identifiers within the
  alembic.stamp command has been improved with many new tests and
  use cases added.

  References: #473

• [autogenerate] [bug] Improved the Python rendering of a series of migration operations such that
  a single "pass" is rendered for a UpgradeOps or
  DowngradeOps based on if no lines of Python code actually
  rendered under the operation, rather than whether or not sub-directives
  exist. Removed extra "pass" lines that would generate from the
  ModifyTableOps directive so that these aren't duplicated under
  operation rewriting scenarios.

  References: #550

• [feature] [runtime] Added new feature MigrationContext.autocommit_block(), a special
  directive which will provide for a non-transactional block inside of a
  migration script. The feature requres that: the database driver
  (e.g. DBAPI) supports the AUTOCOMMIT isolation mode. The directive
  also necessarily needs to COMMIT the existing transaction in progress
  in order to enter autocommit mode.

  References: #123

• [change: py3k] Python 3.4 support is dropped, as the upstream tooling (pip, mysqlclient)
  etc are already dropping support for Python 3.4, which itself is no longer
  maintained.

• [autogenerate] [usecase] Added autogenerate support for Column objects that have
  dialect-specific **kwargs, support first added in SQLAlchemy 1.3.
  This includes SQLite "on conflict" as well as options used by some
  third party dialects.

  References: #518

• [autogenerate] [usecase] Added rendering for SQLAlchemy Variant datatypes, which render as the
  base type plus one or more .with_variant() method calls.

  References: #131

• [commands] [feature] Added "post write hooks" to revision generation. These allow custom logic
  to run after a revision Python script is generated, typically for the
  purpose of running code formatters such as "Black" or "autopep8", but may
  be used for any arbitrary post-render hook as well, including custom Python
  functions or scripts. The hooks are enabled by providing a
  [post_write_hooks] section in the alembic.ini file. A single hook
  is provided which runs an arbitrary Python executable on the newly
  generated revision script, which can be configured to run code formatters
  such as Black; full examples are included in the documentation.

  References: #307

• [commands] [usecase] Made the command interface revision lookup behavior more strict in that an
  Alembic revision number is only resolved based on a partial match rules if
  it has at least four characters, to prevent simple typographical issues
  from inadvertently running migrations.

  References: #534

• [environment] [feature] Added new flag --package to alembic init. For environments where
  the Alembic migration files and such are within the package tree and
  importable as modules, this flag can be specified which will add the
  additional __init__.py files in the version location and the
  environment location.

  References: #463

• [autogenerate] [bug] Fixed bug where rendering of comment text for table-level comments within
  Operations.create_table_comment() and
  Operations.drop_table_comment() was not properly quote-escaped
  within rendered Python code for autogenerate.

  References: #549

• [autogenerate] [bug] Modified the logic of the Rewriter object such that it keeps a
  memoization of which directives it has processed, so that it can ensure it
  processes a particular directive only once, and additionally fixed
  Rewriter so that it functions correctly for multiple-pass
  autogenerate schemes, such as the one illustrated in the "multidb"
  template. By tracking which directives have been processed, a
  multiple-pass scheme which calls upon the Rewriter multiple times
  for the same structure as elements are added can work without running
  duplicate operations on the same elements more than once.

  References: #505