Turn Python warnings into errors

It's generally good practice to run unit tests with warnings turned into errors to ensure deprecation warnings are honoured in a timely manner. Despite often coming across people saying that this can be done with a command line flag, after a bit of searching around I couldn't find a simple example of how to do this.

After a bit of trial and error it turns out to be very simple:

python -W error foo.py

The above flag will turn all warnings into errors.

For more complex usage Doug Hellman has a good write up: http://doughellmann.com/PyMOTW/warnings/

Enabling Upstart user jobs to start at boot.

I've come across an issue with Upstart – user jobs' start on stanzas aren't honored at boot time.

The real issue is more general: user jobs aren't loaded into Upstart until the user creates an Upstart session. If a job isn't loaded into Upstart, it's basically invisible and hence its start on stanzas won't be honored.

Loading user jobs into Upstart is simple. It happens automatically when a user creates an Upstart session by connecting via D-Bus using initctl or one of the shortcuts (e.g. start or status). Until user jobs are loaded into Upstart, they're completely disabled.

So the problem at boot time is that user's don't have the opportunity to create an Upstart session prior to the rc-sysinit job emitting runlevel, this makes it impossible for user jobs with start on runlevel [2345] to be honored.

Perhaps this is by design – I'm not sure – but I wrote the following job to get around the issue by blocking rc-sysinit and creating an Upstart session for each user with an .init/ directory in their home:

The following job should be installed into /etc/init/load-user-jobs.conf:

Can't exec "dpkg-architecture" … on Ubuntu 11.10

Ran into a puzzling problem today setting up PostgreSQL 9.1. After creating a user and logging in, I was greeted with:

$ psql postgres brad
Can't exec "dpkg-architecture": No such file or directory at /usr/bin/psql line 103.
Use of uninitialized value $multiarch in scalar chomp at /usr/bin/psql line 104.
psql (9.1.3)
Type "help" for help.

postgres=#

It seems the package dpkg-dev wasn't installed for some reason…

Easy fix:

sudo apt-get install dpkg-dev

Compiling Python on OSX 10.8

Python 2.6 – OSX Lion

./configure MACOSX_DEPLOYMENT_TARGET=10.7
make
make install

py.test paremeterized test fails with "LookupError: no factory found for function argument …"

I have a trivial test:

import pytest
@pytest.mark.parameterize(("input", "expected"), [
    ("3+5", 8),
    ("2+4", 6),
    ("6*9", 42),
])
def test_eval(input, expected):
    assert eval(input) == expected

It fails saying:

LookupError: no factory found for function argument 'input'
available funcargs: pytestconfig, capsys, capfd, tmpdir, monkeypatch, recwarn
use 'py.test --funcargs [testpath]' for help on them.

What's going on here? It's spelt parametrize – not parameterize.

But why didn't I get a NameError?

pytest.mark allows arbitrary marks to be added to a function. Due to the
dynamic nature of py.test, pytest.mark.<any name here> can be used to mark a
test. Since pytest.mark.parameterize isn't recognised by any of the pytest
plugins, it's essentially a no-op.

Problem cloning local git repository using `git clone file:///…`

So I was trying to clone a local git repository using:

$ git clone file:///home/git/repositories/bar.git

And I would get output like this:

$ git clone file:///home/git/repositories/bar.git/ bar
Initialized empty Git repository in /home/brad/bar/.git
remote: Counting objects: 1317, done.
remote: Compressing objects: 100% (1179/1179), done.
remote: Total 1317 (delta 601), reused 406 (delta 57)
Receiving objects: 100% (1317/1317), 5.37 MiB | 683 KiB/s, done.
Resolving deltas: 100% (601/601), done.
warning: remote HEAD refers to nonexistent ref, unable to checkout.

The issue was that although I had added myself to the git group, the permissions on the heads refs did not permit group read:

$ ls -lha /home/git/repositories/bar.git/refs/heads
total 12K
drwx------ 2 git git 4.0K 2012-03-05 15:42 .
drwx------ 4 git git 4.0K 2012-02-28 14:21 ..
-rw------- 1 git git   41 2012-03-05 15:45 development
-rw------- 1 git git   41 2012-03-05 15:42 master

Simple fix:

$ chmod g+r /home/git/repositories/bar.git/refs/heads/*

So why was this suddenly a problem?

It just so happens I recently upgraded from gitosis to gitolite, and gitolite uses a different umask (0077) to gitosis. This means that every new file created was created with only user permissions.

I want g+rx, so I edited /home/git/.gitolite.rc and changed $REPO_UMASK to 0027.

Remove items from print spool/queue in Windows 7

I've recently had some trouble deleting/removing a print job/item from the printer spool/queue on Windows 7. The print job just wouldn't delete despite rebooting and instructing Windows to delete it many times. After a bit of googling I found a solution:

1. Open a command window (Click Start; Type command and press enter)
2. Right click the title bar and select "Run as Administrator"
3. Type net stop spooler and press enter.
4. Type del %systemroot%\System32\spool\printers\* /Q and press enter.
5. Type net start spooler and press enter.