144 lines
4.6 KiB
Plaintext
144 lines
4.6 KiB
Plaintext
.. default-role:: literal
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===============================
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Configuration handling basics
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===============================
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Tiramisu is made of almost three main objects :
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- :class:`tiramisu.config.Config` witch is the whole configuration entry point
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- :class:`tiramisu.option.Option` stands for the option types
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- :class:`tiramisu.option.OptionDescription` is the shema, the option's structure
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Accessing the configuration `Option`'s
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-----------------------------------------
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The `Config` object attribute access notation stands for the value of the
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configuration's `Option`. That is, the `Config`'s object attribute is the name
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of the `Option`, and the value is the value accessed by the `__getattr__`
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attribute access mechanism.
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If the attribute of the `Config` called by `__getattr__` has not been set before
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(by the classic `__setattr__` mechanism), the default value of the `Option`
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object is returned, and if no `Option` has been declared in the
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`OptionDescription` (that is the schema of the configuration), an
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`AttributeError` is raised.
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::
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>>> gcdummy = BoolOption('dummy', 'dummy', default=False)
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>>> gcdummy._name
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'dummy'
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>>> gcdummy.getdefault()
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False
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>>> descr = OptionDescription('tiramisu', '', [gcdummy])
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>>> cfg = Config(descr)
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>>> cfg.dummy
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False
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>>> cfg.dummy = True
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>>> cfg.dummy
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True
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>>> cfg.idontexist
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AttributeError: 'OptionDescription' object has no attribute 'idontexist'
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The configuration `Option` objects (in this case the `BoolOption`), are
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organized into a tree into nested `OptionDescription` objects. Every
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option has a name, as does every option group. The parts of the full
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name of the option are separated by dots: e.g.
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``config.optgroup.optname``.
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Let's make the protocol of accessing a config's attribute explicit
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(because explicit is better than implicit):
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1. If the option has not been declared, an `AttributeError` is raised,
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2. If an option is declared, but neither a value nor a default value has
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been set, the returned value is `None`,
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3. If an option is declared and a default value has been set, but no value
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has been set, the returned value is the default value of the option,
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4. If an option is declared, and a value has been set, the returned value is
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the value of the option.
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But there are special exceptions. We will see later on that an option can be a
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:term:`mandatory option`. A mandatory option is an option that must have a defined value.
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If no value have been set yet, the value is `None`.
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When the option is called to retrieve a value, an exception is raised.
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What if a value has been set and `None` is to be returned again ? Don't
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worry, an option value can be "reseted" with the help of the `option.Option.reset()`
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method.
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If you know the path:
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::
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>>> config.gc.dummy
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False
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Setting the values of the options
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----------------------------------------
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An important part of the setting of the configuration consists of setting the
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values of the configuration options. There are different ways of setting values,
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the first one is of course the `__setattr__` method
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::
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cfg.name = value
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And if you wanna come back to a default value, use the builtin `del()` function::
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del(cfg.name)
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.. module:: tiramisu.config
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The handling of options is split into two parts: the description of
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which options are available, what their possible values and defaults are
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and how they are organized into a tree. A specific choice of options is
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bundled into a configuration object which has a reference to its option
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description (and therefore makes sure that the configuration values
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adhere to the option description).
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Configuration's interesting methods
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------------------------------------------
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A `Config` object is informed by an `option.OptionDescription`
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instance. The attributes of the ``Config`` objects are the names of the
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children of the ``OptionDescription``.
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Here are the (useful) methods on ``Config`` (or `SubConfig`).
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.. currentmodule:: tiramisu.config
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.. class:: Config
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.. autoclass:: SubConfig
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:members: find, find_first, __iter__, iter_groups, iter_all, make_dict
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.. automethod:: __init__
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.. rubric:: Summary
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.. autosummary::
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find
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find_first
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__iter__
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iter_groups
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iter_all
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make_dict
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.. rubric:: Methods
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A :class:`~config.CommonConfig` is a abstract base class. A
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:class:`~config.SubConfig` is an just in time created objects that wraps an
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::class:`~option.OptionDescription`. A SubConfig differs from a Config in the
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::fact that a config is a root object and has an environnement, a context wich
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::defines the different properties, access rules, vs... There is generally only
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::one Config, and many SubConfigs.
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