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diff --git a/docs/api/runtime-settings.txt b/docs/api/runtime-settings.txt new file mode 100644 index 000000000..2d60aa3e1 --- /dev/null +++ b/docs/api/runtime-settings.txt @@ -0,0 +1,192 @@ +=========================== + Docutils Runtime Settings +=========================== + +:Author: David Goodger +:Contact: goodger@python.org +:Date: $Date$ +:Revision: $Revision$ +:Copyright: This document has been placed in the public domain. + +.. contents:: + + +Introduction +============ + +Docutils runtime settings are assembled from several sources: +component settings specifications, application settings +specifications, configuration files, and command-line options. +Docutils overlays default and explicitly specified values from these +sources such that settings behave the way we want and expect them to +behave. + +To understand how Docutils deals with runtime settings, the attributes +and parameters involved must first be understood. Begin with the the +docstrings of the attributes of the ``docutils.SettingsSpec`` base +class (in the ``docutils/__init__.py`` module): + +* ``settings_spec`` +* ``settings_defaults`` +* ``settings_default_overrides`` +* ``relative_path_settings`` +* ``config_section`` +* ``config_section_dependencies`` + +Next, several _`convenience function parameters` are also significant +(described in the ``docutils.core.publish_programmatically`` function +docstring): + +* The ``settings`` parameter is a runtime settings + (``docutils.frontend.Values``) object which, if present, is assumed + to be complete (it must include all runtime settings). Also, if the + ``settings`` parameter is present, no further runtime settings + processing is done. In other words, the other parameters, described + below, will have no effect. + +* ``settings_spec``, a `docutils.SettingsSpec` subclass or object, is + treated like a fourth component (after the Parser, Reader, and + Writer). In other words, it's the settings specification for the + "Application" itself. + +* ``settings_overrides`` is a dictionary which will override the + defaults of the components (from their settings specs). + +* ``config_section`` specifies the name of an application-specific + configuration file section. + + +.. _command-line tools: + +Runtime Settings Processing for Command-Line Tools +================================================== + +Following along with the actual code is recommended. The +``docutils/__init__.py``, ``docutils/core.py``, and +``docutils.frontend.py`` modules are described. + +1. A command-line front-end tool imports and calls + ``docutils.core.publish_cmdline``. The relevant `convenience + function parameters`_ are described above. + +2. ``docutils.core.publish_cmdline`` initializes a + ``docutils.core.Publisher`` object, then calls its ``publish`` + method. + +3. The ``docutils.core.Publisher`` object's ``publish`` method checks + its ``settings`` attribute to see if it's defined. If it is, no + further runtime settings processing is done. + + If ``settings`` is not defined, ``self.process_command_line`` is + called with the following relevant arguments: + + * ``settings_spec`` + * ``config_section`` + * ``settings_overrides`` (in the form of excess keyword + arguments, collected in the ``defaults`` parameter) + +4. ``self.process_command_line`` calls ``self.setup_option_parser``, + passing ``settings_spec``, ``config_section``, and ``defaults``. + +5. ``self.setup_option_parser`` checks its ``config_section`` + parameter; if defined, it adds that config file section to + ``settings_spec`` (or to a new, empty ``docutils.SettingsSpec`` + object), replacing anything defined earlier. (See `Docutils + Configuration Files`_ for details.) Then it instantiates a new + ``docutils.frontend.OptionParser`` object, passing the following + relevant arguments: + + * ``components``: A tuple of ``docutils.SettingsSpec`` objects, + ``(self.parser, self.reader, self.writer, settings_spec)`` + * ``defaults`` (originally from ``settings_overrides``) + +6. The ``docutils.frontend.OptionParser`` object's ``__init__`` method + calls ``self.populate_from_components`` with ``self.components``, + which consists of ``self`` prepended to the ``components`` tuple it + received. ``self`` (``docutils.frontend.OptionParser``) defines + general Docutils settings. + +7. In ``self.populate_from_components``, for each component passed, + ``component.settings_spec`` is processed and + ``component.settings_defaults`` is applied. Then, for each + component, ``component.settings_default_overrides`` is applied. + This two-loop process ensures that + ``component.settings_default_overrides`` can override the default + settings of any other component. + +8. Back in ``docutils.frontend.OptionParser.__init__``, the + ``defaults`` parameter (derived from the ``settings_overrides`` + parameter of ``docutils.core.Publisher.publish``) is overlaid over + ``self.defaults``. So ``settings_overrides`` has priority over all + ``SettingsSpec`` data. + +9. Next, ``docutils.frontend.OptionParser.__init__`` checks if + configuration files are enabled (its ``read_config_files`` + parameter is true, and ``self.defaults['_disable_config']`` is + false). If they are enabled (and normally, they are), + ``self.get_standard_config_settings`` is called. This reads the + `docutils configuration files`_, and returns a dictionary of + settings. This is then overlaid on ``self.defaults``. So + configuration file settings have priority over all software-defined + defaults. + +10. Back in the ``docutils.core.Publisher`` object, + ``self.setup_option_parser`` returns the ``option_parser`` object + to its caller, ``self.process_command_line``. + +11. ``self.process_command_line`` calls ``option_parser.parse_args``, + which parses all command line options and returns a + ``docutils.frontend.Values`` object. This is assigned to the + ``docutils.core.Publisher`` object's ``self.settings``. So + command-line options have priority over configuration file + settings. + + When ``option_parser.parse_args`` is called, the source and + destination command-line arguments are also parsed, and assigned + to the ``_source`` and ``_destination`` attributes of what becomes + the ``docutils.core.Publisher`` object's ``self.settings``. + +12. From ``docutils.core.Publisher.publish``, ``self.set_io`` is + called with no arguments. If either ``self.source`` or + ``self.destination`` are not set, the corresponding + ``self.set_source`` and ``self.set_destination`` are called, + effectively with no arguments. + +13. ``self.set_source`` checks for a ``source_path`` parameter, and if + there is none (which is the case for command-line use), it is + taken from ``self.settings._source``. ``self.source`` is set by + instantiating a ``self.source_class`` object. For command-line + front-end tools, the default ``self.source_class`` is used, + ``docutils.io.FileInput``. + +14. ``self.set_destination`` does the same job for the destination + that ``self.set_source`` does for the source (the default + ``self.destination_class`` is ``docutils.io.FileOutput``). + +.. _Docutils Configuration Files: ../user/config.html + + +Runtime Settings Processing From Applications +============================================= + +Applications process runtime settings in a different way than +`command-line tools`_ do. Instead of calling ``publish_cmdline``, the +application calls one of ``publish_file``, ``publish_string``, or +``publish_parts``. These in turn call ``publish_programmatically``, +which implements a generic programmatic interface. Although an +application may also call ``publish_programmatically`` directly, it is +not recommended (if it does seem to be necessary, please write to the +Docutils-develop_ mailing list). + +``publish_programmatically`` accepts the same `convenience function +parameters`_ as ``publish_cmdline``. Where things differ is that +programmatic use does no command-line processing. Instead of calling +``docutils.Publisher.process_command_line`` (as ``publish_cmdline`` +does, via ``docutils.Publisher.publish``), +``docutils.Publisher.process_programmatic_settings`` is called to set +up the runtime settings. + +.. copy & modify the list from command-line tools? + + +.. _Docutils-develop: ../user/mailing-lists.html#docutils-develop |