infi.conf 0.0.16

Generic configuration mechanism

Overview

infi.conf is a generic mechanism for storing, loading and manipulating configuration.

Usage

Basics

Given a file like this:

>>> f = open("/tmp/my_file.cfg", "w")
>>> _ = f.write("""
... CONFIG = {
...    "a" : {
...       "b" : 2,
...    }
... }""")
>>> f.close()

Obtaining a configuration object is done via:

>>> from infi.conf import Config
>>> c = Config.from_filename("/tmp/my_file.cfg")
>>> c.root.a.b
2

Loading From Other Sources

You can also load from string:

>>> c = Config.from_string("CONFIG = {'a' : 2}")
>>> c.root.a
2

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

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))))
>>> from infi.conf.utils import assign_path
>>> assign_path(c, "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. infi.conf’s utilities provide a function for this:

>>> from infi.conf.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