Configuration

Note

this section discusses the internal API of Alembic as regards internal configuration constructs. This section is only useful for developers who wish to extend the capabilities of Alembic. For documentation on configuration of an Alembic environment, please see Tutorial.

The Config object represents the configuration passed to the Alembic environment. From an API usage perspective, it is needed for the following use cases:

  • to create a ScriptDirectory, which allows you to work with the actual script files in a migration environment
  • to create an EnvironmentContext, which allows you to actually run the env.py module within the migration environment
  • to programatically run any of the commands in the Commands module.

The Config is not needed for these cases:

class alembic.config.Config(file_=None, ini_section='alembic', output_buffer=None, stdout=<open file '<stdout>', mode 'w'>, cmd_opts=None, config_args=immutabledict({}), attributes=None)

Represent an Alembic configuration.

Within an env.py script, this is available via the EnvironmentContext.config attribute, which in turn is available at alembic.context:

from alembic import context

some_param = context.config.get_main_option("my option")

When invoking Alembic programatically, a new Config can be created by passing the name of an .ini file to the constructor:

from alembic.config import Config
alembic_cfg = Config("/path/to/yourapp/alembic.ini")

With a Config object, you can then run Alembic commands programmatically using the directives in alembic.command.

The Config object can also be constructed without a filename. Values can be set programmatically, and new sections will be created as needed:

from alembic.config import Config
alembic_cfg = Config()
alembic_cfg.set_main_option("script_location", "myapp:migrations")
alembic_cfg.set_main_option("url", "postgresql://foo/bar")
alembic_cfg.set_section_option("mysection", "foo", "bar")

Warning

When using programmatic configuration, make sure the env.py file in use is compatible with the target configuration; including that the call to Python logging.fileConfig() is omitted if the programmatic configuration doesn’t actually include logging directives.

For passing non-string values to environments, such as connections and engines, use the Config.attributes dictionary:

with engine.begin() as connection:
    alembic_cfg.attributes['connection'] = connection
    command.upgrade(alembic_cfg, "head")
Parameters:
  • file_ – name of the .ini file to open.
  • ini_section – name of the main Alembic section within the .ini file
  • output_buffer – optional file-like input buffer which will be passed to the MigrationContext - used to redirect the output of “offline generation” when using Alembic programmatically.
  • stdout

    buffer where the “print” output of commands will be sent. Defaults to sys.stdout.

    New in version 0.4.

  • config_args

    A dictionary of keys and values that will be used for substitution in the alembic config file. The dictionary as given is copied to a new one, stored locally as the attribute .config_args. When the Config.file_config attribute is first invoked, the replacement variable here will be added to this dictionary before the dictionary is passed to SafeConfigParser() to parse the .ini file.

    New in version 0.7.0.

  • attributes

    optional dictionary of arbitrary Python keys/values, which will be populated into the Config.attributes dictionary.

    New in version 0.7.5.

Construct a new Config

attributes

A Python dictionary for storage of additional state.

This is a utility dictionary which can include not just strings but engines, connections, schema objects, or anything else. Use this to pass objects into an env.py script, such as passing a sqlalchemy.engine.base.Connection when calling commands from alembic.command programmatically.

New in version 0.7.5.

cmd_opts = None

The command-line options passed to the alembic script.

Within an env.py script this can be accessed via the EnvironmentContext.config attribute.

New in version 0.6.0.

config_file_name = None

Filesystem path to the .ini file in use.

config_ini_section = None

Name of the config file section to read basic configuration from. Defaults to alembic, that is the [alembic] section of the .ini file. This value is modified using the -n/--name option to the Alembic runnier.

file_config

Return the underlying ConfigParser object.

Direct access to the .ini file is available here, though the Config.get_section() and Config.get_main_option() methods provide a possibly simpler interface.

get_main_option(name, default=None)

Return an option from the ‘main’ section of the .ini file.

This defaults to being a key from the [alembic] section, unless the -n/--name flag were used to indicate a different section.

get_section(name)

Return all the configuration options from a given .ini file section as a dictionary.

get_section_option(section, name, default=None)

Return an option from the given section of the .ini file.

get_template_directory()

Return the directory where Alembic setup templates are found.

This method is used by the alembic init and list_templates commands.

print_stdout(text, *arg)

Render a message to standard out.

set_main_option(name, value)

Set an option programmatically within the ‘main’ section.

This overrides whatever was in the .ini file.

Parameters:
  • name – name of the value
  • value – the value. Note that this value is passed to ConfigParser.set, which supports variable interpolation using pyformat (e.g. %(some_value)s). A raw percent sign not part of an interpolation symbol must therefore be escaped, e.g. %%. The given value may refer to another value already in the file using the interpolation format.
set_section_option(section, name, value)

Set an option programmatically within the given section.

The section is created if it doesn’t exist already. The value here will override whatever was in the .ini file.

Parameters:
  • section – name of the section
  • name – name of the value
  • value – the value. Note that this value is passed to ConfigParser.set, which supports variable interpolation using pyformat (e.g. %(some_value)s). A raw percent sign not part of an interpolation symbol must therefore be escaped, e.g. %%. The given value may refer to another value already in the file using the interpolation format.
alembic.config.main(argv=None, prog=None, **kwargs)

The console runner function for Alembic.