jraylan/configparser

backport of configparser from Python 3

This package is a backport of the refreshed and enhanced ConfigParser from later Python versions. To use the backport instead of the built-in version, simply import it explicitly as a backport:

from backports import configparser

To use the backport on Python 2 and the built-in version on Python 3, use the standard invocation:

import configparser

For detailed documentation consult the vanilla version at http://docs.python.org/3/library/configparser.html.

Why you'll love configparser

Whereas almost completely compatible with its older brother, configparser sports a bunch of interesting new features:

• full mapping protocol access (more info):

  >>> parser = ConfigParser()
  >>> parser.read_string("""
  [DEFAULT]
  location = upper left
  visible = yes
  editable = no
  color = blue
  
  [main]
  title = Main Menu
  color = green
  
  [options]
  title = Options
  """)
  >>> parser['main']['color']
  'green'
  >>> parser['main']['editable']
  'no'
  >>> section = parser['options']
  >>> section['title']
  'Options'
  >>> section['title'] = 'Options (editable: %(editable)s)'
  >>> section['title']
  'Options (editable: no)'
  

• there's now one default ConfigParser class, which basically is the old SafeConfigParser with a bunch of tweaks which make it more predictable for users. Don't need interpolation? Simply use ConfigParser(interpolation=None), no need to use a distinct RawConfigParser anymore.

• the parser is highly customizable upon instantiation supporting things like changing option delimiters, comment characters, the name of the DEFAULT section, the interpolation syntax, etc.

• you can easily create your own interpolation syntax but there are two powerful implementations built-in (more info):

  • the classic %(string-like)s syntax (called BasicInterpolation)
  • a new ${buildout:like} syntax (called ExtendedInterpolation)

• fallback values may be specified in getters (more info):

  >>> config.get('closet', 'monster',
  ...            fallback='No such things as monsters')
  'No such things as monsters'
  

• ConfigParser objects can now read data directly from strings and from dictionaries. That means importing configuration from JSON or specifying default values for the whole configuration (multiple sections) is now a single line of code. Same goes for copying data from another ConfigParser instance, thanks to its mapping protocol support.

• many smaller tweaks, updates and fixes

A few words about Unicode

configparser comes from Python 3 and as such it works well with Unicode. The library is generally cleaned up in terms of internal data storage and reading/writing files. There are a couple of incompatibilities with the old ConfigParser due to that. However, the work required to migrate is well worth it as it shows the issues that would likely come up during migration of your project to Python 3.

The design assumes that Unicode strings are used whenever possible [1]. That gives you the certainty that what's stored in a configuration object is text. Once your configuration is read, the rest of your application doesn't have to deal with encoding issues. All you have is text [2]. The only two phases when you should explicitly state encoding is when you either read from an external source (e.g. a file) or write back.

Versioning

This project uses semver to communicate the impact of various releases while periodically syncing with the upstream implementation in CPython. The changelog serves as a reference indicating which versions incorporate which upstream functionality.

Prior to the 4.0.0 release, another scheme was used to associate the CPython and backports releases.

Maintenance

This backport was originally authored by Łukasz Langa, the current vanilla configparser maintainer for CPython and is currently maintained by Jason R. Coombs:

• configparser repository
• configparser issue tracker

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Conversion Process

This section is technical and should bother you only if you are wondering how this backport is produced. If the implementation details of this backport are not important for you, feel free to ignore the following content.

The project takes the following branching approach:

• The 3.x branch holds unchanged files synchronized from the upstream CPython repository. The synchronization is currently done by manually copying the required files and stating from which CPython changeset they come.
• The master branch holds a version of the 3.x code with some tweaks that make it compatible with older Pythons. Code on this branch must work on all supported Python versions. Test with tox or in CI.

The process works like this:

1. In the 3.x branch, run pip-run -- sync-upstream.py, which downloads the latest stable release of Python and copies the relevant files from there into their new locations and then commits those changes with a nice reference to the relevant upstream commit hash.
2. Check for new names in __all__ and update imports in configparser.py accordingly. Optionally, run the tests on a late Python 3. Commit.
3. Merge the new commit to master. Run tests. Commit.
4. Make any compatibility changes on master. Run tests. Commit.
5. Update the docs and release the new version.

Footnotes

[1]

To somewhat ease migration, passing bytestrings is still supported but they are converted to Unicode for internal storage anyway. This means that for the vast majority of strings used in configuration files, it won't matter if you pass them as bytestrings or Unicode. However, if you pass a bytestring that cannot be converted to Unicode using the naive ASCII codec, a UnicodeDecodeError will be raised. This is purposeful and helps you manage proper encoding for all content you store in memory, read from various sources and write back.

[2]

Life gets much easier when you understand that you basically manage text in your application. You don't care about bytes but about letters. In that regard the concept of content encoding is meaningless. The only time when you deal with raw bytes is when you write the data to a file. Then you have to specify how your text should be encoded. On the other end, to get meaningful text from a file, the application reading it has to know which encoding was used during its creation. But once the bytes are read and properly decoded, all you have is text. This is especially powerful when you start interacting with multiple data sources. Even if each of them uses a different encoding, inside your application data is held in abstract text form. You can program your business logic without worrying about which data came from which source. You can freely exchange the data you store between sources. Only reading/writing files requires encoding your text to bytes.