Hacking Python SDK » History » Version 14

Version 13 (Tom Clegg, 08/26/2014 09:43 AM) → Version 14/24 (Peter Amstutz, 08/29/2014 09:10 PM)

h1. Hacking Python SDK


h2. Prerequisites

The FUSE driver requires associated libraries to build:

sudo apt-get install libattr1-dev libfuse-dev pkg-config fuse
sudo adduser "$USER" fuse
sudo chmod g+rw /dev/fuse
sudo chown root:fuse /dev/fuse

After installing @fuse@ and adding yourself to the @fuse@ group, you need to start a new login session. Make sure the @groups@ command reports that you're in the @fuse@ group.

h2. Get the source code

git clone https://github.com/curoverse/arvados.git

h2. virtualenv

virtualenv helps you isolate the dependencies for a specific package or environment, much like Bundler does for our Rails applications. The recommended way to deploy is to build a virtualenv for Arvados development.

To build the virtualenv, run:

$ virtualenv --setuptools VENVDIR

(@VENVDIR@ can be a directory anywhere you like, although best practice is to keep it outside your source directory.)

To set up the shell to use the isolated virtualenv environment, run:

$ source VENVDIR/bin/activate

To learn more about using and configuring virtualenv, read the "virtualenv usage documentation":https://virtualenv.pypa.io/en/latest/virtualenv.html#usage.

h2. Run tests

# Set up the environment to use a dedicated virtualenv
# Run the client library test suite
# Build a client library package and install it to the virtualenv
# Run the FUSE driver test suite
# Build a FUSE driver package and install it to the virtualenv

Note: The test suite brings up a Keep server and an API server to run tests against. For best results:
* Try [[Hacking Keep]] and [[Hacking API Server]] to make sure you have all the right dependencies for running the Keep and API servers.
* Make sure you have a blob_signing_key in services/api/config/application.yml
* Install the keepstore binary.
** Make sure your GOPATH points somewhere, e.g.: @export GOPATH=~/gocode; mkdir -p $GOPATH@
** Install keepstore: @go get git.curoverse.com/arvados.git/services/keepstore@
** (if you don't do anything special, this fetches "master" from git.curoverse.com -- if you want to build a version of keepstore with local modifications, see [[Hacking Keep]])

Script (make sure to edit the first line to refer to your virtualenv):

source VENVDIR/bin/activate

cd ~/arvados/sdk/python
python setup.py test
python setup.py egg_info -b ".$(git log --format=format:%ct.%h -n1 .)" sdist rotate --keep=1 --match .tar.gz
pip install dist/arvados-python-client-0.1.*.tar.gz

cd ~/arvados/services/fuse
python setup.py test
python setup.py egg_info -b ".$(git log --format=format:%ct.%h -n1 .)" sdist rotate --keep=1 --match .tar.gz
pip install dist/arvados_fuse-0.1.*.tar.gz

h3. Run a single test or test class

source VENVDIR/bin/activate
cd ~/arvados/sdk/python

# One test module
python setup.py test --test-suite tests.test_keep_locator

# One test class
python setup.py test --test-suite tests.test_keep_locator.ArvadosKeepLocatorTest

# One test case
python setup.py test --test-suite tests.test_keep_locator.ArvadosKeepLocatorTest.base_locators

h2. Logging

The Python SDK uses Python's built-in logging module to log errors, warnings, and debug messages. The arvados module sets up logging for messages under "arvados" based on local configuration (e.g., the @ARVADOS_DEBUG@ setting). Other SDK modules and command-line tools should @import arvados@ and then send messages to a logger under "arvados" to ensure consistent log handling. Typical setup looks like this:

<pre><code class="python">
import arvados
import logging

logger = logging.getLogger('arvados.YOURTHING')

Once you've set this up, you can send messages to the logger using methods like @logger.debug()@ and @logger.error()@. See the "Logger class documentation":https://docs.python.org/2/library/logging.html#logger-objects for full details.

Command-line scripts may reconfigure the @arvados.logger@ object based on additional configuration like command-line switches. @services/fuse/bin/arv-mount@ demonstrates adjusting the level and setting a custom log handler.

h2. Python buffer protocol

Notes on managing buffers efficiently in Python, we don't use this in the python sdk as of this writing (but we might).


Example using bytearray() to allocate a buffer, memoryview() to create a writable slice, and readinto() to write directly to the buffer slice:

>>> b = bytearray(20)
>>> c = memoryview(b)
>>> f = open("python.txt", "r")
>>> f.readinto(c[5:10])
>>> b
bytearray(b"\x00\x00\x00\x00\x00I\'ve \x00\x00\x00\x00\x00\x00\x00\x00\x00\x00")