other:python:misc_by_jyp
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other:python:misc_by_jyp [2021/06/30 15:20] jypeter |
other:python:misc_by_jyp [2021/07/07 13:07] jypeter Added the paths/filenames section |
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| </WRAP> | </WRAP> | ||
| - | * Reading/setting environments variables\\ <code>>>> os.environ['TMPDIR'] | + | ==== Reading/setting environments variables ==== |
| + | |||
| + | |||
| + | <code>>>> os.environ['TMPDIR'] | ||
| '/data/jypmce/climafcache' | '/data/jypmce/climafcache' | ||
| >>> os.environ.get('SCRATCHDIR', '/data/jypmce/some_scratch_stuff') | >>> os.environ.get('SCRATCHDIR', '/data/jypmce/some_scratch_stuff') | ||
| Line 14: | Line 17: | ||
| </code> | </code> | ||
| - | * 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 | + | ==== 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 | ||
| * <code>raise RuntimeError('\n\nOMG! An error! :-(\nAborting script...')</code> | * <code>raise RuntimeError('\n\nOMG! An error! :-(\nAborting script...')</code> | ||
| * [[https://docs.python.org/3/tutorial/errors.html|Errors and Exceptions tutorial]] | * [[https://docs.python.org/3/tutorial/errors.html|Errors and Exceptions tutorial]] | ||
| * [[https://docs.python.org/3/library/exceptions.html|Built-in Exceptions reference]] | * [[https://docs.python.org/3/library/exceptions.html|Built-in Exceptions reference]] | ||
| - | * Stopping a script\\ <code>sys.exit('Some optional message about why we are stopping')</code> | ||
| - | * Checking if a file/directory is writable by the current user\\ <code>>>> os.access('/', os.W_OK) | + | ==== 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 | ||
| + | |||
| + | <code>sys.exit('Some optional message about why we are stopping')</code> | ||
| + | |||
| + | |||
| + | ==== Checking if a file/directory is writable by the current user ==== | ||
| + | |||
| + | <code>>>> os.access('/', os.W_OK) | ||
| False | False | ||
| >>> os.access('/home/jypmce/.bashrc', os.W_OK) | >>> os.access('/home/jypmce/.bashrc', os.W_OK) | ||
| True</code> | True</code> | ||
| + | |||
| + | ==== Working with paths and filenames ==== | ||
| + | |||
| + | If you are in a hurry, you can just use string functions to work with path and file names. But you will need some specific functions to check if a file exists, and similar operations. All these are available in 2 libraries that have similar functions. Both of these libraries can deal with Unix-type paths on Linux computers, and Windows-type paths on Windows computers | ||
| + | |||
| + | * [[https://docs.python.org/3/library/os.path.html|os.path]] //Common pathname manipulations// | ||
| + | * Available since... a long time! Use this if you want to avoid backward compatibility problems | ||
| + | * Some functions are directly in [[https://docs.python.org/3/library/os.html|os]] //Miscellaneous operating system interfaces//\\ e.g. [[https://docs.python.org/3/library/os.html#os.remove|os.remove]] and [[https://docs.python.org/3/library/os.html#os.rmdir|os.rmdir]] | ||
| + | * [[https://docs.python.org/3/library/pathlib.html|pathlib]] //Object-oriented filesystem paths// | ||
| + | * Available since Python version 3.4 | ||
| + | * [[https://docs.python.org/3/library/pathlib.html#correspondence-to-tools-in-the-os-module|Matching pathlib, and os or os.path functions]] | ||
| + | ==== Using command-line arguments ==== | ||
| + | |||
| + | === The extremely easy but non-flexible way: sys.argv === | ||
| + | |||
| + | 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 ''argv_test.py'' test script: | ||
| + | <code>#!/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)</code> | ||
| + | |||
| + | <code>$ python argv_test.py | ||
| + | Number of script arguments (including script name) = 1 | ||
| + | 0 argv_test.py | ||
| + | |||
| + | $ python argv_test.py tas tas_tes.nc | ||
| + | Number of script arguments (including script name) = 3 | ||
| + | 0 argv_test.py | ||
| + | 1 tas | ||
| + | 2 tas_tes.nc</code> | ||
| + | |||
| + | === The C-style way: getopt === | ||
| + | |||
| + | Use [[https://docs.python.org/3/library/getopt.html|getopt]] (//C-style parser for command line options//) | ||
| + | |||
| + | === The deprecated Python way: optparse === | ||
| + | |||
| + | [[https://docs.python.org/3/library/optparse.html|optparse]] (//parser for command line options//) is **deprecated since Python version 3.2**! You should now use argparse (check [[https://docs.python.org/3/library/argparse.html#upgrading-optparse-code|Upgrading optparse code]] for converting from ''optparse'' to ''argparse'') | ||
| + | |||
| + | === The current Python way: argparse === | ||
| + | |||
| + | [[https://docs.python.org/3/library/argparse.html|argparse]] (//parser for command-line options, arguments and sub-commands//) is available since Python version 3.2 | ||
| /* | /* | ||
| - | * tip template\\ <code>Some code</code> | + | ==== Tip template ==== |
| + | |||
| + | <code>Some code</code> | ||
| */ | */ | ||
other/python/misc_by_jyp.txt · Last modified: 2024/04/19 12:02 by jypeter
