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Useful python stuff

You will find on this page some useful, but unsorted, python tips and tricks that can't fit in a section of the main JYP's recommended steps for learning python page

Reading/setting environments variables

>>> os.environ['TMPDIR']
>>> os.environ.get('SCRATCHDIR', '/data/jypmce/some_scratch_stuff')
>>> os.environ['temporary_env_var_for_THIS_script'] = 'some value'
>>> os.environ['temporary_env_var_for_THIS_script']
'some value'

Generating (aka raising) an error

This will stop the script, unless it is called in a function, and the code calling the function explicitely catches and deals with errors

Stopping a script

A user can use CTRL-C or kill to stop a script, or CTRL-Z to suspend it temporarily (use fg to resume a suspended script). The code below can be used by the script itself to interrupt its execution, instead of raising an error

sys.exit('Some optional message about why we are stopping')

Checking if a file/directory is writable by the current user

>>> os.access('/', os.W_OK)
>>> os.access('/home/jypmce/.bashrc', os.W_OK)

Using command-line arguments

The fast but non-flexible way

The name of a script, the number of arguments (including the name of the script), and the arguments (as strings) can be accessed through the sys.argv strings' list

Simple test script:

#!/usr/bin/env python
import sys
nb_args = len(sys.argv)
print('Number of script arguments (including script name) =', nb_args)
for idx, val in enumerate(sys.argv):
    print(idx, val)
$ python
Number of script arguments (including script name) = 1

$ python tas
Number of script arguments (including script name) = 3
1 tas

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other/python/misc_by_jyp.1625570718.txt.gz · Last modified: 2021/07/06 11:25 by jypeter