Hacking Python SDK » History » Version 21

Nico César, 06/05/2015 07:34 PM

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h1. Hacking Python SDK
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{{toc}}
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h2. Prerequisites
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The FUSE driver requires associated libraries to build:
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<pre>
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sudo apt-get install libattr1-dev libfuse-dev pkg-config fuse
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sudo adduser "$USER" fuse
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sudo chmod g+rw /dev/fuse
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sudo chown root:fuse /dev/fuse
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</pre>
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After installing @fuse@ and adding yourself to the @fuse@ group, you need to start a new login session. Make sure the @groups@ command reports that you're in the @fuse@ group.
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h2. Get the source code
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<pre>
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cd
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git clone https://github.com/curoverse/arvados.git
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</pre>
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h2. virtualenv
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virtualenv helps you isolate the dependencies for a specific package or environment, much like Bundler does for our Rails applications.  The recommended way to deploy is to build a virtualenv for Arvados development.
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To build the virtualenv, run:
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<pre>
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$ sudo apt-get install virtualenv
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$ virtualenv --setuptools VENVDIR
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</pre>
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(@VENVDIR@ can be a directory anywhere you like, although best practice is to keep it outside your source directory.)
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To set up the shell to use the isolated virtualenv environment, run:
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<pre>
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$ source VENVDIR/bin/activate
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</pre>
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To learn more about using and configuring virtualenv, read the "virtualenv usage documentation":https://virtualenv.pypa.io/en/latest/virtualenv.html#usage.
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h2. Run tests
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Strategy:
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# Set up the environment to use a dedicated virtualenv
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# Run the client library test suite
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# Build a client library package and install it to the virtualenv
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# Run the FUSE driver test suite
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# Build a FUSE driver package and install it to the virtualenv
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Note: The test suite brings up a Keep server and an API server to run tests against. For best results:
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* Try [[Hacking Keep]] and [[Hacking API Server]] to make sure you have all the right dependencies for running the Keep and API servers.
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* Make sure you have a blob_signing_key in services/api/config/application.yml
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* Install the keepstore binary.
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** Make sure your GOPATH points somewhere, e.g.: @export GOPATH=~/gocode; mkdir -p $GOPATH@
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** Install keepstore: @go get git.curoverse.com/arvados.git/services/keepstore@
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** (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]])
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Script (make sure to edit the first line to refer to your virtualenv):
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<pre>
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source VENVDIR/bin/activate
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cd ~/arvados/sdk/python
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python setup.py test
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python setup.py install
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cd ~/arvados/services/fuse
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python setup.py test
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python setup.py install
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</pre>
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h3. Run a single test or test class
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<pre>
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source VENVDIR/bin/activate
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cd ~/arvados/sdk/python
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# One test module
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python setup.py test --test-suite tests.test_keep_locator
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# One test class
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python setup.py test --test-suite tests.test_keep_locator.ArvadosKeepLocatorTest
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# One test case
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python setup.py test --test-suite tests.test_keep_locator.ArvadosKeepLocatorTest.base_locators
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</pre>
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h2. Builds and versioning
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When we build each Python package, the version number is generated from the most recent commit that affected the package.  The format is @0.1.[commit's timestamp formatted as %Y%m%d%H%M%S].[commit's short hash]@.
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If you want to make changes in one package and refer to it somewhere else (e.g., have the FUSE package depend on a specific SDK version), you should commit your changes to the original package before anything else.  Then you can consistently refer to the metadata from that dedicated commit in subsequent changes.
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h2. Logging
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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:
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<pre><code class="python">
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import arvados
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import logging
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logger = logging.getLogger('arvados.YOURTHING')
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</code></pre>
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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.
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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.
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h2. Documenting your code
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See "PEP 257":https://www.python.org/dev/peps/pep-0257/ and "PEP 287":https://www.python.org/dev/peps/pep-0287/
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h2. Python buffer protocol
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Notes on managing buffers efficiently in Python, we don't use this in the python sdk as of this writing (but we might).
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http://eli.thegreenplace.net/2011/11/28/less-copies-in-python-with-the-buffer-protocol-and-memoryviews/
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Example using bytearray() to allocate a buffer, memoryview() to create a writable slice, and readinto() to write directly to the buffer slice:
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<pre>
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>>> b = bytearray(20)
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>>> c = memoryview(b)
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>>> f = open("python.txt", "r")
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>>> f.readinto(c[5:10])
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5
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>>> b
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bytearray(b"\x00\x00\x00\x00\x00I\'ve \x00\x00\x00\x00\x00\x00\x00\x00\x00\x00")
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</pre>