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Generic configuration mechanism

Project description

Confetti is a Python library for dealing with hierarchical configuration data.

Updating Paths

Setting paths is done by settings items:

>>> c['a'] = 3
>>> c.root.a
3

Setting paths that didn’t exist before is not allowed, unless you assign a config object:

>>> c['b'] = 3 #doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
 ...
CannotSetValue: Cannot set key 'b'

>>> c['b'] = Config(2)
>>> c.root.b
2

Assigning can also be done via the root proxy:

>>> c.root.a = 3
>>> c.root.a
3

Backing Up/Restoring

Whenever you want to preserve the configuration prior to a change and restore it later, you can do it with backup() and restore(). They work like a stack, so they push and pop states:

>>> c = Config({"value":2})
>>> c['value']
2
>>> c.backup()
>>> c['value'] = 3
>>> c['value']
3
>>> c.backup()
>>> c['value'] = 4
>>> c['value']
4
>>> c.restore()
>>> c['value']
3
>>> c.restore()
>>> c['value']
2

Metadata

You can store metadata on config variables and paths. This is useful for documenting paths or for attaching arbitrary information:

>>> from confetti import Metadata
>>> c = Config({
...     "key" : "value" // Metadata(some_key="some_value"),
...     })

It can later be retrieved:

>>> c.get_config("key").metadata
{'some_key': 'some_value'}

Metadata can also be attached to config branches:

>>> c = Config({
...     "key" : {
...         "a" : 1,
...         "b" : 2,
...         } // Metadata(doc="this is a nested dict")
...     }) // Metadata(doc="and this is the root")
>>> c.metadata
{'doc': 'and this is the root'}
>>> c.get_config("key").metadata
{'doc': 'this is a nested dict'}

Utilities

Path Assignment

It is possible to assign to a config via path assignment, e.g:

>>> c = Config(dict(a=dict(b=dict(c=3))))
>>> c.assign_path("a.b.c", 4)
>>> c.root.a.b.c
4

Expression Path Assignment

In some cases you would like to receive strings like this:

a.b.c=2

And make sense of them in the context of the configuration. This might be because they originate from command line, overlay files, or whatever other source comes to mind. confetti’s utilities provide a function for this:

>>> from confetti.utils import assign_path_expression
>>> assign_path_expression(c, "a.b.c=2")
>>> c.root.a.b.c
'2'

Note that in this method, types are always strings. If your leaf already has a value, the deduce_type flag can be used to deduce the type from the current value:

>>> c['a']['b']['c'] = 3
>>> assign_path_expression(c, 'a.b.c=666', deduce_type=True)
>>> c.root.a.b.c
666

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