Arvados

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h1. Writing Crunch scripts in Python

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h3. How to read your input file from the json template

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h3. How to write your file to a collection

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h3. How to run an external command

Usually this is most convenient:

<pre>

import subprocess

foo = subprocess.check_output(['echo','foo'])

</pre>

If the output is big, redirect it to a file:

<pre>

import subprocess

with open('/tmp/foo', 'w') as outfile:

    subprocess.check_call(['head', '-c', '1234567', '/dev/urandom'], stdout=outfile)

</pre>

h3. How to create new tasks per input file in a collection

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h3. Where to put temporary files

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h3. How to write data directly to Keep with native Python code

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