1. What’s New?

As part of moving towards PEP-8 compliance a number of name changes are being made to methods and class attributes with each release. There is a module, pyslet.pep8, which contains a compatibility class for remapping missing class attribute names to their new forms and generating deprecation warnings, run your code with “python -Wd” to force these warnings to appear. As Pyslet makes the transition to Python 3 some of the old names will go away completely.

It is still possible that some previously documented names could now fail (module level functions, function arguments, etc.) but I’ve tried to include wrappers or aliases so please raise an issue on Github if you discover a bug caused by the renaming. I’ll restore any missing old-style names to improve backwards compatibility on request.

Finally, in some cases you are encouraged to derive classes from those defined by Pyslet and to override default method implementations. If you have done this using old-style names you will have to update your method names to prevent ambiguity. I have added code to automatically detect most problems and force fatal errors at runtime on construction, the error messages should explain which methods need to be renamed.

1.1. Version Numbering

Pyslet version numbers use the check-in date as their last component so you can always tell if one build is newer than another. At the moment there is only one actively maintained branch of the code: version ‘0”. Changes are reported against the versions released to PyPi. ‘XX’ at the end of the version indicates changes that have not yet been released to PyPi but have been committed to the master branch (with tests passing).

Not sure which version you are using? Try:

from pyslet.info import version
print version

1.2. Version 0.6.20160201

Summary of New Features:
LTI module rewritten, now suitable for real applications! WSGI-based web-app framework built using Pyslet’s DAL MySQL Database connector for Pyslet’s DAL SSL, Certificates and HTTP Basic Authentication HTTP Cookies URNs

#3 PEP-8 driven refactoring (ongoing)

Added new method decorators to make supporting renamed and redirected methods easier. Added checks for ambiguous names in classes likely to have been sub-classed by third-party code.

#8 Support for SSL Certificates in HTTP Clients

Fixed certificate support in OData and Atom clients. See blog post for further information on how to use certificates: http://swl10.blogspot.co.uk/2014/11/basic-authentication-ssl-and-pyslets.html

#9 HTTP client retry strategy

Improved HTTP retries with simple Fibonacci-based back-off. Also fixed a bug where, if the first request after a server timed out an idle connection is a POST, the request would fail.

#12 bug when using numeric or named parameters in DB API

The basic bug is fixed and I’ve also added support for paramstyle ‘format’.

#14 content element missing in media-link entries

Fixed. Affected atom xml formatted entities only.

#15 MySQL implementation of Pyslet’s DAL (ongoing)

Changes to the core DAL to deal to better support other DB modules. These included added support for LIMIT clauses to speed up paged access to large entity sets. Implementation of a retry strategy when database commands return OperationalError (e.g., MySQL idle timeouts). An updated connection pool manager and an optional pool cleaner method to clean up idle database connections.

#18 Possible bug in parsing AssociationSet names

Added a compatibility mode to odata2.csdl to enable the metadata model to optionally accept hyphen or dash characters in simple identifiers using:

import pyslet.odata2.csdl as edm

#19 OData Function parameter handling

Enabled function parameter passing in OData service operations. Only primitive types are supported but they are now parsed correctly from the query string and coerced to the declared parameter type. Bound functions now receive them as a dictionary of SimpleValue instances.

#20 HTTP Basic Authentication

Fixed an issue with the OData basic authentication support, in some cases the HTTP client was waiting for a 401 when it could have offered the credentials preemptively. See also the following blog article: http://swl10.blogspot.co.uk/2014/11/basic-authentication-ssl-and-pyslets.html

#22 Support for navigation properties in OData expressions

Although the code always contained support in general, the mapping to SQL did not previously support the use of table joins in SQL expressions. This release adds support for joins (but not for nested joins).

#23 A Framework for WSGI-based LTI Applications

Added a new module to make it easier to write WSGI-based applications. Re-factored the existing Basic LTI module to use the new oauthlib and Pyslet’s own OData-inspired data access layer.

#24 ESA Sentinel mission compatibility

Added the capability to override the metadata used by an OData server to deal with validation issues in some services. Clients can now also be created from an offline copy of the service root document.

#26 HTTP client eats memory when downloading large unchunked files

Fixed the download buffer which was failing to write out data until an entire chunk (or the entire download) was complete.

#29 https connections fail on POST after remote server hangup

Partial mitigation with an agressive 2s window in which to start sending a follow-up request when pipelining through https. This is a crude solution and the bug remains open for a more robust solution based around use of the Expect header in HTTP/1.1.

#30 HTTP client cleanup thread

Added an optional parameter to the HTTP client constructor that creates a cleanup thread to close down idle connections periodically.

#31 Removed reliance on Host header in wsgi app class

There are a number of ways an application can be attacked using a forged Host header, wsgi now ignores the Host header and uses a new setting for the preferred scheme//host:port.

#32 get_certificate_chain

Implemented a function to create a complete certificate chain. Implemented using pyOpenSSL with a lot of help from this article

#33 Fixed exception: ‘NoneType’ object has no attribute ‘current_thread’ on exit

Caused by an overly ambitious __del__ method in SQLEntityContainer.

#34 Fixed missing Edm prefix in OData sample code #35 Fixed missing import in rfc5023 (atom protocol) module #36 Fixed incorrect error messages in OData $filter queries #37 Extended comparison operators in OData to include DateTimeOffset values

All thanks to @ianwj5int for spotting

#38 Python 3 compatibility work

I have started revising modules to support Python 3. This is not yet production ready but it is a small impact on existing modules. I have done my best to maintain compatibility, in practice code should continue to work with no changes required.

The most likely failure mode is that you may find a unicode string in Python 2 where you expected a plain str. This can have a knock-on effect of promoting data to unicode, e.g., through formatting operations. In general the returned types of methods are just being clarified and unicode values are returned only where they may have been returned previously anyway. However, in the case of the URI attributes in the rfc2396 module the types have changed from str to unicode in this release.

This is work in progress but the impact is likely to be minimal at this stage.

#40 & #41 Composite keys and Slug headers

Key hints were not working properly between the OData client and server implementations, and were not working at all when the key was composite. It is now possible to pass the formatted entity key predicate (including the brackets) as a Slug to the OData server and it will attempt to parse it and use that key where allowed by the underlying data layer.

#43 Fixes for Python running on Windows

The only substantive changes required were to the way we check for io failures when IOError is raised and the way we handle URI containing non-ASCII characters. Some of the unit tests were also affected due to issues with timing, including the reduced precision of time.time() on Windows-based systems.

Untracked enhancements:

Added a new module to support HTTP cookies. The HTTP/OData client can now be configured to accept cookies. The default behaviour is to ignore them so this won’t affect existing applications.

Added a new module to support URN syntax to provide a better implementation of the IMS LTI vocabularies.

Added an optional params dictionary to the OData expression parser to make it much easier to parse parameterized OData queries.

Added new methods for creating and executing drop table statements in the DAL.

Reworked sample code for the weather data server, included example driver files for mod_wsgi

Other fixes:

Fixed an issue in the OData client that caused basic key lookup in filtered entity collections to use both a key predicate and a $filter query option. This was causing the filter to be ignored, now the key predicate will be added to the filter rather than the path segment.

Fixed the OData DateTime parser to accept (and discard) any time zone specifier given in the literal form as it is now allowed in the ABNF and may therefore be generated by OData servers.

Fixed a bug in the OData server which meant that requests for JSON format responses were not being limited by the builtin topmax and would therefore attempt to return all matching entities in a single response.

Fixed a bug in the OData server which meant that use of $count was causing the $filter to be ignored!

Fixed a bug in the OData URI parser that prevent compound keys from working properly when zealous escaping was used.

Fixed a bug in the OData server which meant that error messages that contained non-ASCII characters were causing a 500 error due to character encoding issues when outputting the expected OData error format.

Fixed a bug in the OData expression evaluator when evaluating expressions that traversed navigation properties over optional relations. If there was no associated entity an error was being raised.

Fixed a bug in the SQL DAL implementation which means that navigation properties that require joining across a composite key were generating syntax errors, e.g., in SQLite the message ‘near “=”: syntax error’ would be seen.

Fixed a bug in the SQLite DAL implementation which means that in-memory databases were not working correctly in multi-threaded environments.

Fixed XML parser bug, ID elements in namespaced documents were not being handled properly.

Fixed bug in the OData server when handling non-URI characters in entity keys

Fixed a bug with composite key handling in media streams when using the SQL layer

1.3. Version 0.5.20140801

Summary of New Features:

  • OData Media Resources
  • HTTP Package refactoring and retry handling
  • Python 2.6 Support

Tracked issues addressed in this release:

#1 added a Makefile to make it easier for others to build and develop the code

Added a tox.ini file to enable support for tox (a tool for running the unittests in multiple Python environments).

#3 PEP-8 driven refactoring (ongoing)

#2 Migrated the code from SVN to git: https://github.com/swl10/pyslet

#4 Added support for read-only properties and tests for auto generated primary and foreign key values

#6 added integration between git and travis ci (thanks @sassman for your help with this)

#10 restored support for Python 2.6

1.3.1. Other Fixes

OData URLs with reserved values in their keys were failing. For example Entity(‘why%3F’) was not being correctly percent-decoded by the URI parsing class ODataURI. Furthermore, the server implementation was fixed to deal with the fact that PATH_INFO in the WSGI environ dictionary follows the CGI convention of being URL-decoded.

1.4. Version 0.4 and earlier

These are obsolete, version 0.4 was developed on Google Code as an integral part of the QTI Migration tool.

1.5. PyAssess

A precursor to Pyslet. For more information see: https://code.google.com/p/qtimigration/wiki/PyAssess