What follows is essentially a stream-of-consciousness dump from the PyATL meeting on August 20.
Introduction to Python and Sqlite3
Presented by Alfredo Deza
- For simple things, it’s blazing fast
- It’s local, so no network necessary
- Serializes to a single file
- Uses DB-API 2.0 (see PEP 249). Once you have your
cursor, you can start running SQL.
- NOTE: Use
sqlite3.connect(':memory:', isolation_level='exclusive')to use an in-memory DB
iterdump()method of the sqlite3 connection gives you an iterable that lets you export the in-memory database. This is handy if you want to write them all to a file.
- Although the sqlite3 docs claim that the concurrency situation has improved, the Internet at large seems to indicate that problems still abound.
Presented by Skylar Saveland
- Recommend you use PostGIS w/ PostgresQL
- OpenLayers is a nice library for embedding map widgets on any webpage.
- Core team is available on IRC (
- They make it fairly easy to integrate with Google Maps
- Instead of standard Django
models, you use the one from GeoDjango and then you get the
Polygonetc. so that you can store GIS data right with your Django models
- You can do distance, intersection, touches, etc. queries right in the ORM
Nuts & Bolts
Presented by Brandon Rhodes
PyCon is 6 months away
- String formatting
- New in 2.6
unicodeobjects now have a
format()method, and that’s the encouraged way to do string formatting;
%is right out.
- At least one of the benefits of the new method is that it’s easier to read the name-based format
- It lets you use dot-notation to access attributes of parameters
- Also supports indexing into lists, etc.
- I need to look this up, pronto. It’s covered briefly in the sequence types in the standard docs and links to a dedicated page for the new syntax.
- lxml != ElementTree
- The goal of ElementTree is to be a Pythonic XML library
- It’s probably a dead project, since the current version is 2 years old
- lxml uses the “ElementTree” object model, but it’s built on top of libxml2 and libxslt so it’s blazing fast.
- Remember these two imports:
from lxml import etree
from lxml.cssselect import CSSSelector as css
- lxml also supports CSS selectors
- Don’t forget the default for lxml is an XML parser; you want the HTML parser
- Ian Bicking says lxml is better than BeautifulSoup
Making Code More Testable
Presented by Brandon Rhodes
- Based on Writing Testable Code; showing Python examples of how some of these actually look when you put them in action
Don’t Mix Object Graph Construction with Application Logic
- This one makes it really hard to test classes in isolation, because instantiating one starts instantiating a bunch of objects we don’t want to test.
- On a side note, nose handily shows you captured
stdoutwhen a test fails, and doesn’t show you when the test is successful. That way you can you leave your debugging print statements. It does not capture
- The simple fix for this in Python is to accept dependencies in the
__init__method. You might recognize this as constructor-based dependency injection. In Java, mutator-based dependency injection is more common.
Avoid “Global State”
- Even though every programmer (should) know global state is evil, you still see this quite often in web apps where the global state is something like the request and/or session.
- The breakage is quite often far more extensive than you would expect, e.g., a test in one file that doesn’t handle global state well can break tests in other files, even if they are doing a good job of handling the global state.
- The fix is to pass the state explicitly, even if the state has to be passed to a lot of functions. This is inconvenient at times, but is usually worth it.
Back to flipping out…