Python - Cachetools LRUCache KeyError

If your application is threaded and you’re getting a “KeyError” while using the non-decorator version of cachetool’s LRUCache, then you need to put whatever is manipulating the cache object inside of a lock. Also, since LRUCache is modified when values are gotten from it, you will also need to make sure you’re locking when you get values from cache too. If you can use the decorator version of LRUCache, that’s preferred since it has built-in locking.

Here’s an example of the error:

And an example of the fix: https://bitbucket.org/zzzeek/dogpile.cache/pull-requests/32/add-a-cachetools-lru-lfu-in-memory-backend/diff#comment-22242704

Javascript's Round vs PHP's Round

Today I learned that by default PHP rounds differently than javascript.

PHP (using the default PHP_ROUND_HALF_UP)

php > echo round(-1.5);
-2

“Round val up to precision decimal places away from zero, when it is half way there. Making 1.5 into 2 and -1.5 into -2.”

https://secure.php.net/manual/en/function.round.php

Javascript

Math.round(-1.5);
-1

“For negative numbers, if the decimal portion is exactly -0.5, the return value is the smallest integer that is greater than the number.”

https://msdn.microsoft.com/en-us/library/5cza0web(v=vs.94).aspx

Django-Moderation

It would be nice if there were a sqlalchemy/flask equivalent to this: https://github.com/dominno/django-moderation

The equivalent might use sqlalchemy_utils for its generic relationships: https://sqlalchemy-utils.readthedocs.io/en/latest/generic_relationship.html

Modified Preorder Tree Traversal

This was a great explanation of Modified Preorder Tree Traversal (or MPTT): https://www.sitepoint.com/hierarchical-data-database-2/

A common use-case for MPTT is categorization data, like with the way django-oscar uses django-mptt: https://github.com/django-mptt/django-mptt

Datatables - Uncaught TypeError: Cannot read property 'style' of undefined

If you see this error in datatables: “Uncaught TypeError: Cannot read property ‘style’ of undefined”

It’s likely that you’re missing a header column in your table. Make sure you have the same number of <th> elements as items in the “columns” section of your datatables initialization.

Select2 Replacement

This selectize.js library looks like a good replacement for Select2: selectize.js

Javascript Data Tables

Updated 2026-09-08: mindmup/editable-table and daniel-nagy/md-data-table are now archived on GitHub. Swapped the SlickGrid link for 6pac/SlickGrid, the actively maintained fork of the original.

• https://fooplugins.github.io/FooTable/index.html - good, no inline editing though
• https://datatables.net/ - editable plugin requires purchase
• https://github.com/6pac/SlickGrid - actively maintained fork; the original mleibman/SlickGrid is unmaintained
• https://handsontable.com/ - responsiveness doesn’t work very well
• https://github.com/mindmup/editable-table - only supports editing, now archived
• https://github.com/David-Mulder/paper-datatable - pretty, but doesn’t seem very battle-tested
• https://www.ag-grid.com/ - no tests
• https://github.com/angular-ui/ui-grid - requires angular
• ng-table - requires angular
• http://backgridjs.com/ - requires backbone
• https://github.com/daniel-nagy/md-data-table - pretty, but requires angular, now archived
• jQuery Dynatable - not editable
• http://www.jtable.org/ - last updated in 2014, styling looks dated
• https://datazenit.com/static/sensei-grid/examples/ - simple, editable

Falsehoods programmers believe about time and time zones

This article has a lot of great lessons learned about timezones: Falsehoods programmers believe about time and time zones (archived)

SQLAlchemy - JSON not changing on commit

If your changes to a JSON, JSONB, or HSTORE field aren’t saving after you commit, then you need to wrap your field in the MutableDict shown here: http://docs.sqlalchemy.org/en/latest/dialects/postgresql.html#sqlalchemy.dialects.postgresql.HSTORE

SQLAlchemy - AttributeError: type object 'JSONB' has no attribute 'lower'

This error happened because I mistyped “db.column” instead of “db.Column” when I was creating my database model using SQLAlchemy.

This might be your problem if db.create_all() isn’t creating all the columns you expected.