191 lines
5.5 KiB
Plaintext
191 lines
5.5 KiB
Plaintext
.. default-role:: literal
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===============================
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Configuration handling basics
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===============================
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`Config` and `Option` objects
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================================
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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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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 do not want to use the pythonic way, that is the attribute access
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way to obtain the value of the configuration option, you can also search
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for it recursively in the whole config namespaces with the ``get()``
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method :
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::
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>>> config.get('bool')
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True
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To find the right option, `get()` searches recursively into the whole
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tree. For example, to find an option which is in the `gc` namespace
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there are two possibilites.
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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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If you don't remember the path:
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::
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>>> config.get('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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wich has the same effect that the "global" `set()` method (it expects that
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the value owner is the default)
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::
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cfg.set(name=value)
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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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The configuration object important methods
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---------------------------------------------
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`config.Config()` object that lives in `config.py` hold the
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choosen values for the options (or the default value for the
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`option.Option()` object, if no choice was made).
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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``:
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.. currentmodule:: tiramisu.config
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.. autoclass:: Config
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.. automethod:: __init__
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.. rubric:: Methods
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.. autosummary::
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~Config.__init__
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~Config.set
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.. automethod:: set
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We can see that values can also be config objects, it's the
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sub-namespaces that are stored in the values as `Config()` objects.
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convenience utilities (iteration, exports...)
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-----------------------------------------------
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With this `config.Config()` configuration management entry point,
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it is possible to
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- `iter` on config, notice that there is an iteration order wich is
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the order of the :ref:`optdescr` specification entries,
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- compare two configs (equality),
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- export the whole config into a `dict` with `config.make_dict()`,
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`option.Option()` objects in a config are iterable in the pythonic
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way, that is something like `[(name, value) for name, value in config]`.
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To iter on groups in the same manner, use the
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`config.Config.iter_groups()` method wich yields generators too.
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**iteration utilities**
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.. autoclass:: Config
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.. automethod:: __init__
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.. rubric:: Methods
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.. autosummary::
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~Config.get
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~Config.find
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~Config.find_first
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~Config.getpaths
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~Config.iter_groups
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~Config.__iter__
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.. automethod:: get
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.. automethod:: find
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.. automethod:: find_first
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.. automethod:: getpaths
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.. automethod:: iter_groups
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.. automethod:: __iter__
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