Creating debtcollector

https://blueprints.launchpad.net/oslo.utils/+spec/adopt-debtcollector

The goal of this library would be to provide well documented developer facing deprecation patterns that start of with the a basic set and can expand into a larger set of patterns as time goes on (it would not start off being a library that would be used for operator facing deprecation, as that is already covered by the versionutils.py module in the oslo-incubator).

For example the following patterns could be considered common:

  • Deprecating a keyword argument to be later replaced with a replacement keyword argument (useful when a new name was later determined to be better than an initial name).
  • Altering the name of a property to refer to a new and improved name (useful when say a property name is discovered after a certain amount of time to make more sense than an initial property name).
  • Moving a class (with or without breaking those who are inheriting from your old location); this is useful when a class is better located at a different (potentially better named, more meaningfully named) module than it was initially placed at (this is common when the initial location was thought of to be a good location, but after usage a alternative location would make more sense).
  • ...

The desired output of these patterns would be an application of the warnings module that would use the common functions that module provides to emit DeprecationWarning or PendingDeprecationWarning or similar derivative to developers using libraries (or potentially applications) about future deprecations.

Since the warnings module supports different types of actions we should take advantage of that capability (or extend it as needed) to avoid creating a bunch of garbage messages that will appear for the developers using deprecated features/functionality.

For example the library/functions provided should be affected by the warnings modules action strings that are defined/copied below.

Value Disposition
error turn matching warnings into exceptions
ignore never print matching warnings (the default in python 2.7+)
always always print matching warnings
default print the first occurrence of matching warnings for each location where the warning is issued
module print the first occurrence of matching warnings for each module where the warning is issued
once print only the first occurrence of matching warnings, regardless of location

Using these settings appropriately would be expected to help avoid polluting logs or sys.stderr where these messages can show up (we should look into how to make these messages visible in the openstack CI system, and less/not visible in a released library).

To aid in this process it might be useful to hook into the following (but this can be for later discussion):

https://docs.python.org/2/library/logging.html#logging.captureWarnings

Depending on future functionality we could let applications use the logging.captureWarnings function, or provide this in oslo.log or do something different (the point being that the warnings module and supporting API will be the entrypoint that these patterns use, how applications or other libraries adapt/plugin to the warnings module can be adjusted and tweaked as seen fit).

Library Name

debtcollector

Contents

  • debtcollector/__init__.py
  • debtcollector/utils.py (internal utils, not for public usage)
  • debtcollector/moves.py (for patterns common to moving code/classes/properties...)
  • debtcollector/renames.py (for patterns common to renaming code/classes/properties...)
  • ... (others as patterns emerge)

Early Adopters

  • Taskflow
  • Others?

Public API

Current idea for API (will likely evolve as new patterns appear...)

  • debtcollector/moves.py
# Patterns devoted to 'moving' functions, methods, classes, arguments...

def moved_decorator(kind, new_attribute_name, message=None,
                    version=None, removal_version=None,
                    stacklevel=3)

 # Creates a decorator of the given kind for the given attribute name
 # with the provided message, version deprecated in, the version it will
 # be removed in and the given stacklevel (used to output the users code
 # location when this decorator is called).
 #
 # An example message:
 >>> kind = 'Property'
 >>> new_attribute_name = 'a'
 >>> what = "%s '%s' has moved to '%s" % (kind, 'b', new_attribute_name)
 >>> deprecation._generate_moved_message(what, message='sorry its going away', version='0.1', removal_version='0.2')
 "Property 'a' has moved to 'b' in version '0.1' and will be removed in version '0.2': sorry its going away"

 def moved_property(new_attribute_name, message=None,
                    version=None, removal_version=None, stacklevel=3):

 # Decorator specialization of moved_decorator that sets the kind to
 # a property instead of allowing it to be specified.

 def moved_class(new_class, old_class_name, old_module_name, message=None,
                 version=None, removal_version=None, stacklevel=3):

 # Same as moved_decorator but for classes, returns a class proxy that can
 # not be inherited from (useful for when the user of this is aware that no
 # inheritance is happening)

 def moved_class_inheritable(new_class, old_class_name, old_module_name, message=None,
                             version=None, removal_version=None, stacklevel=3):

 # Same as moved_class but for classes, returns a new-old class that can
 # be inherited from (useful for when the user of this is unaware if any
 # inheritance is happening)

 ...
  • debtcollector/renames.py
# Patterns devoted to 'renaming' functions, methods, classes, arguments...

def renamed_kwarg(old_name, new_name, message=None,
                  version=None, removal_version=None, stacklevel=3):

# Creates a decorator that can be applied to a keyword argument accepting
# method, function, callable that will warn the user of that function
# when they are using the old, to be removed keyword argument; creates
# an appropriate message telling the user this (in a similar format
# as mentioned above).

...
  • debtcollector/utils.py
# Generic *internal* library used utils...

def generate_message(prefix, postfix=None, message=None,
                     version=None, removal_version=None):

# Generates the messages for renames or moves in a common (share as much
# as possible manner) so that the messages look and feel like they are
# coming from a common library

...

Implementation

Assignee(s)

Primary assignee:

  • Harlowja

Other contributors:

  • You?

Primary maintainer

Primary maintainer:

  • Harlowja (@yahoo)

Other contributors:

  • Szhukov (@yahoo)
  • You?

Security Contact

Security Contact: harlowja

Milestones

Target Milestone for completion: kilo-2

Work Items

  • Change owner of Launchpad project (make it part of the Oslo projectgroup)
  • Give openstackci Owner permissions on PyPI
  • Create Initial Repository
  • Make the library do something
  • Update the README.rst
  • Publish git repo
  • Oslo team review new repository
  • Infra project configuration
  • Update Gerrit Groups and ACLs
  • openstack-infra/devstack-gate adjustments
  • openstack/requirements projects.txt adjustments
  • Update project list on docs.openstack.org
  • Tag a release
  • Profit!

Adoption Notes

N/A

Dependencies

Requirements

Note

All of the currently planned dependencies are in the requirements repository.

References

Note

This work is licensed under a Creative Commons Attribution 3.0 Unported License. http://creativecommons.org/licenses/by/3.0/legalcode