ConfigObj New Features

[fuzz...@voidspace.org.uk]

ConfigObj New Features

A new version of ConfigObj is now available. As well as a few bugfixes (and the file size shrinking 40% due to the separation of the tests and changelog), there are several important new features.

Despite being relatively easy to code, these greatly extend the capabilities of ConfigObj. These extracts from the docs summarise what is new.

• Empty Values are now valid syntax, with a new option to write them
• Copy Mode allows the creation of default config files from a configspec, including comments
• unrepr mode allows for the storing and retrieving of basic Python datatypes

Empty values

From Empty Values.

Many config files from other applications allow empty values. As of version 4.3.0, ConfigObj will read these as an empty string.

A new option/attribute has been added (write_empty_values) to allow ConfigObj to write empty strings as empty values.

from configobj import ConfigObj
cfg = '''
    key =
    key2 = # a comment
'''.splitlines()
config = ConfigObj(cfg)
print config
{'key': '', 'key2': ''}

config.write_empty_values = True
for line in config.write():
    print line

key =
key2 =     # a comment

Copy Mode

From Copy Mode.

Because you can specify default values in your configspec, you can use ConfigObj to write out default config files for your application.

However, normally values supplied from a default in a configspec are not written out by the write method.

To do this, you need to specify copy=True when you call validate. As well as not marking values as default, all the comments in the configspec file will be copied into your ConfigObj instance.

from configobj import ConfigObj
from validate import Validator
vdt = Validator()
config = ConfigObj(configspec='default.ini')
config.filename = 'new_default.ini'
config.validate(vdt, copy=True)
config.write()

Hint

There are functions to assist in the automatic creation of a configspec, in the ConfigPersist Module.

unrepr mode

From unrepr mode.

The unrepr option allows you to store and retrieve the basic Python data-types using config files. It has to use a slightly different syntax to normal ConfigObj files. Unsurprisingly it uses Python syntax.

This means that lists are different (they are surrounded by square brackets), and strings must be quoted.

The types that unrepr can work with are :

strings, lists tuples

None, True, False

dictionaries, integers, floats

longs and complex numbers

You can't store classes, types or instances.

unrepr uses repr(object) to write out values, so it currently doesn't check that you are writing valid objects. If you attempt to read an unsupported value, ConfigObj will raise a configobj.UnknownType exception.

Values that are triple quoted cased. The triple quotes are removed before converting. This means that you can use triple quotes to write dictionaries over several lines in your config files. They won't be written like this though.

If you are writing config files by hand, for use with unrepr, you should be aware of the following differences from normal ConfigObj syntax :

List : ['A List', 'With', 'Strings']

Strings : "Must be quoted."

Backslash : "The backslash must be escaped \\"

These all follow normal Python syntax.

So ConfigObj can now be used for simple (as in easy) data persistence. Move over YAML.

Posted by Fuzzyman on 2006-04-07 22:51:40.
Categories: Projects, Python
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