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other:python:misc_by_jyp [2021/07/06 11:25]
jypeter Started the command-line args section
other:python:misc_by_jyp [2021/10/26 11:42] (current)
jypeter [Sorting] Added content
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 <WRAP center round tip 60%> <WRAP center round tip 60%>
-You will find on this page some useful, but unsorted, python tips and tricks that can't fit in a section of the main [[other:​python:​jyp_steps|JYP'​s recommended steps for learning python]] page+You will find on this page some **useful, but unsorted, python tips and tricks** that can't fit in a section of the main [[other:​python:​jyp_steps|JYP'​s recommended steps for learning python]] page
 </​WRAP>​ </​WRAP>​
  
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 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]]
 +  * [[https://​docs.python.org/​3/​library/​shutil.html|High-level file operations]]
 +
 +
 +=== Example: getting the full path of the Python used ===
 +
 +Note: the actual python may be different from the default python!
 +
 +<​code>​$ which python
 +/​usr/​bin/​python
 +
 +$ /​modfs/​modtools/​miniconda3//​envs/​analyse_3.6_test/​bin/​python
 +>>>​ import sys, shutil
 +>>>​ shutil.which('​python'​)
 +'/​usr/​bin/​python'​
 +>>>​ sys.executable
 +'/​modfs/​modtools/​miniconda3//​envs/​analyse_3.6_test/​bin/​python'</​code>​
 +
 +
 +=== Example: getting the full path of a script ===
 +
 +<​code>>>>​ import os
 +>>>​ os.getcwd()
 +'/​home/​jypmce/​PMIP4'​
 +>>>​ os.path.exists('​./​argv_test.py'​)
 +True
 +>>>​ os.path.abspath('​./​argv_test.py'​)
 +'/​home/​jypmce/​PMIP4/​argv_test.py'​
 +>>>​ os.path.exists('/​home/​jypmce/​PMIP4/​argv_test.py'​)
 +True
 +</​code>​
 +
 +
 +=== Example: getting the size(s) of all the files in a directory ===
 +
 +<​code>​$ cd /​data/​jypmce/​TestDir
 +$ ls -l
 +total 72
 +-rw-r--r-- 1 jypmce ipsl 18147 Jun 25  2012 get_TS_cmip5.py
 +-rw-r--r-- 1 jypmce ipsl 16152 Jun 21  2012 get_TS_cmip5.py~
 +-rw-r--r-- 1 jypmce ipsl 13954 Jul  3  2012 get_TS_cmip5_regular.py
 +-rw-r--r-- 1 jypmce ipsl 16539 Jun 22  2012 get_TS_cmip5_regular.py~</​code>​
 +
 +<​code>>>>​ os.chdir('/​data/​jypmce/​TestDir'​)
 +>>>​ print(os.getcwd())
 +/​data/​jypmce/​TestDir
 +>>>​ files_list = os.listdir()
 +>>>​ files_list
 +['​get_TS_cmip5.py~',​ '​get_TS_cmip5_regular.py',​ '​get_TS_cmip5_regular.py~',​ '​get_TS_cmip5.py'​]
 +>>>​ files_sizes = list(map(os.path.getsize,​ files_list))
 +>>>​ files_sizes
 +[16152, 13954, 16539, 18147]
 +>>>​ sum(files_sizes)
 +64792</​code>​
 +
 +==== Generating file names ====
 +
 +=== Name depending on the current date/time ===
 +
 +<​code>>>>​ import time
 +>>>​ plot_version = time.strftime('​%Y%m%d_%H%M'​)
 +>>>​ f_name = '​test_%s.nc'​ % (plot_version,​)
 +>>>​ f_name
 +'​test_20210827_1334.nc'​
 +</​code>​
 +
 +=== Temporary file ===
 +
 +<​code>>>>​ import tempfile, os
 +>>>​ f_tmp = tempfile.NamedTemporaryFile(mode='​w',​ suffix='​.nc',​ delete=False)
 +>>>​ f_tmp
 +<​tempfile._TemporaryFileWrapper object at 0x2b5614743820>​
 +>>>​ f_tmp.name
 +'/​tmp/​tmpi6uk9hre.nc'​
 +>>>​ f_tmp.close()
 +>>>​ os.remove(f_tmp.name)</​code>​
 ==== Using command-line arguments ==== ==== Using command-line arguments ====
  
-=== The fast but non-flexible way ===+=== 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 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
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 1 tas 1 tas
 2 tas_tes.nc</​code>​ 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
 +
 +==== Using ordered dictionaries ====
 +
 +**Dictionary order is guaranteed to be insertion order**! Note that the [[https://​docs.python.org/​3/​library/​stdtypes.html#​dict|usual Python dictionary]] also guarantees the order since version **3.6**
 +
 +Check the [[https://​docs.python.org/​3/​library/​collections.html#​collections.OrderedDict|OrderedDict class]] (''​from collections import OrderedDict''​) and the [[https://​realpython.com/​python-ordereddict/​|OrderedDict vs dict in Python: The Right Tool for the Job]] tutorial
 +
 +==== Printing a readable version of long lists or dictionaries ====
 +
 +The [[https://​docs.python.org/​3/​library/​pprint.html|pprint]] module can be used for //pretty printing// objects (lists, dictionaries,​ ...). It will wrap long lines in a meaningful way
 +
 +<​code>>>>​ import pprint
 +
 +>>>​ test_dic = {'​AWI-ESM-1-1-LR_AWI':​{'​r1i1p1f1':​ {'​grid':​ '​gn'​}},​ '​CESM2_NCAR':​{'​r1i1p1f1':​ {'​grid':​ '​gn'​}},​ '​IPSL-CM6A-LR_IPSL':​{'​r1i1p1f1':​ {'​grid':​ '​gr'​},​ '​r1i1p1f2':​ {'​grid':​ '​gr'​},​ '​r1i1p1f3':​ {'​grid':​ '​gr'​},​ '​r1i1p1f4':​ {'​grid':​ '​gr'​}}}
 +
 +>>>​ print(test_dic)
 +{'​AWI-ESM-1-1-LR_AWI':​ {'​r1i1p1f1':​ {'​grid':​ '​gn'​}},​ '​CESM2_NCAR':​ {'​r1i1p1f1':​ {'​grid':​ '​gn'​}},​ '​IPSL-CM6A-LR_IPSL':​ {'​r1i1p1f1':​ {'​grid':​ '​gr'​},​ '​r1i1p1f2':​ {'​grid':​ '​gr'​},​ '​r1i1p1f3':​ {'​grid':​ '​gr'​},​ '​r1i1p1f4':​ {'​grid':​ '​gr'​}}}
 +
 +>>>​ pprint.pprint(test_dic)
 +{'​AWI-ESM-1-1-LR_AWI':​ {'​r1i1p1f1':​ {'​grid':​ '​gn'​}},​
 + '​CESM2_NCAR':​ {'​r1i1p1f1':​ {'​grid':​ '​gn'​}},​
 + '​IPSL-CM6A-LR_IPSL':​ {'​r1i1p1f1':​ {'​grid':​ '​gr'​},​
 +                       '​r1i1p1f2':​ {'​grid':​ '​gr'​},​
 +                       '​r1i1p1f3':​ {'​grid':​ '​gr'​},​
 +                       '​r1i1p1f4':​ {'​grid':​ '​gr'​}}}
 +                       
 +>>>​ dir(test_dic)
 +['​__class__',​ '​__contains__',​ '​__delattr__',​ [... lots of unreadable stuff removed...] '​setdefault',​ '​update',​ '​values'​]
 +
 +>>>​ pprint.pprint(dir(test_dic))
 +['​__class__',​
 + '​__contains__',​
 +
 +[... lots of lines removed in this example ]
 +
 + '​setdefault',​
 + '​update',​
 + '​values'​]
 +
 +</​code>​
 +
 +==== Sorting ====
 +
 +  * [[https://​docs.python.org/​3/​howto/​sorting.html|Sorting HOW TO]]
 +  * Example: sorting the keys and the values of a dictionary, and then using the ''​key''​ parameter to sort the keys of a dictionary according to the value associated with the key
 +    * If we provide a ''​key''​ function, the ''​sort''​ function will sort the elements by the values returned by the function, instead of sorting by the initial values. The function used for generating the key below is very simple and we can use a //lambda// (i.e //in place//) function
 +    * <​code>>>>​ demo_dic = {'​a':​10,​ '​b':​5,​ '​c':​-1,​ '​d':​0}
 +
 +>>>​ sorted(demo_dic.keys())
 +['​a',​ '​b',​ '​c',​ '​d'​]
 +
 +>>>​ sorted(demo_dic.values())
 +[-1, 0, 5, 10]
 +
 +>>>​ sorted(demo_dic.keys(),​ key=lambda key_name:​demo_dic[key_name])
 +['​c',​ '​d',​ '​b',​ '​a'​]</​code>​
 +
  
 /* /*
other/python/misc_by_jyp.1625570718.txt.gz · Last modified: 2021/07/06 11:25 by jypeter