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other:python:misc_by_jyp [2022/12/12 12:11]
jypeter Added the "Storing objects and data in a file" section
other:python:misc_by_jyp [2022/12/12 13:50]
jypeter Improved by changing the sections' levels
Line 5: Line 5:
 </​WRAP>​ </​WRAP>​
  
-==== Reading/​setting environments variables ==== 
  
 +===== Reading/​setting environments variables =====
  
 <​code>>>>​ os.environ['​TMPDIR'​] <​code>>>>​ os.environ['​TMPDIR'​]
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 </​code>​ </​code>​
  
-==== Generating (aka raising) an error ====+ 
 +===== 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 This will stop the script, unless it is called in a function, and the code calling the function explicitely catches and deals with errors
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-==== Stopping a script ====+===== 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 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
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-==== Checking if a file/​directory is writable by the current user ====+===== Checking if a file/​directory is writable by the current user =====
  
 <​code>>>>​ os.access('/',​ os.W_OK) <​code>>>>​ os.access('/',​ os.W_OK)
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 True</​code>​ True</​code>​
  
-==== Playing with strings ==== 
  
-=== Filenames, etc... ===+===== Playing with strings ===== 
 + 
 +==== Filenames, etc... ​====
  
 Check [[other:​python:​misc_by_jyp#​working_with_paths_and_filenames|Working with paths and filenames]] and [[other:​python:​misc_by_jyp#​generating_file_names|Generating file names]] Check [[other:​python:​misc_by_jyp#​working_with_paths_and_filenames|Working with paths and filenames]] and [[other:​python:​misc_by_jyp#​generating_file_names|Generating file names]]
  
-=== Splitting strings ===+==== Splitting strings ​====
  
 It's easy to split a string with multiple blank delimiters, or a specific delimiter, but it can be harder to deal with sub-strings It's easy to split a string with multiple blank delimiters, or a specific delimiter, but it can be harder to deal with sub-strings
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 >>>​ shlex.split(complex_string) >>>​ shlex.split(complex_string)
 ['​-o',​ '​1',​ '​--long',​ 'A string with accented chars: \xc3\xa9 \xc3\xa8 \xc3\xa0 \xc3\xa7'​]</​code>​ ['​-o',​ '​1',​ '​--long',​ 'A string with accented chars: \xc3\xa9 \xc3\xa8 \xc3\xa0 \xc3\xa7'​]</​code>​
 +
 +
 ==== Working with paths and filenames ==== ==== Working with paths and filenames ====
  
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 >>>​ f_tmp.close() >>>​ f_tmp.close()
 >>>​ os.remove(f_tmp.name)</​code>​ >>>​ os.remove(f_tmp.name)</​code>​
-==== Using command-line arguments ==== 
  
-=== The extremely easy but non-flexible way: sys.argv ===+ 
 +===== 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 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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 2 tas_tes.nc</​code>​ 2 tas_tes.nc</​code>​
  
-=== The C-style way: getopt ===+ 
 +==== The C-style way: getopt ​====
  
 Use [[https://​docs.python.org/​3/​library/​getopt.html|getopt]] (//C-style parser for command line options//) Use [[https://​docs.python.org/​3/​library/​getopt.html|getopt]] (//C-style parser for command line options//)
  
-=== The deprecated Python way: optparse ===+ 
 +==== 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''​) [[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 ===+ 
 +==== 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 [[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 ====+ 
 +===== 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** **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**
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 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 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
  
-==== Using sets ====+ 
 +===== Using sets =====
  
 [[https://​docs.python.org/​3/​tutorial/​datastructures.html#​sets|Python sets]] are **groups of unique elements**. They can be used to easily find all the unique elements of //​something//​ and you can easily determine the **intersection**,​ **union** (and other similar operations) of sets. [[https://​docs.python.org/​3/​tutorial/​datastructures.html#​sets|Python sets]] are **groups of unique elements**. They can be used to easily find all the unique elements of //​something//​ and you can easily determine the **intersection**,​ **union** (and other similar operations) of sets.
  
-==== Printing a readable version of long lists or dictionaries ====+ 
 +===== 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 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
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 </​code>​ </​code>​
  
-==== Storing objects and data in a file (shelve and friends) ==== 
  
-The built-in [[other:​python:​jyp_steps?s[]=shelve#​the_shelve_package|shelve]] module can be **easily** used for storing temporary/​intermediate data+===== Storing objects and data in a file (shelve and friends) ===== 
 + 
 +The built-in [[other:​python:​jyp_steps#​the_shelve_package|shelve]] module can be **easily** used for storing temporary/​intermediate data
  
 More options: More options:
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   * Working with [[other:​python:​jyp_steps#​netcdf_filesusing_cdms2_xarray_and_netcdf4|NetCDF]] files   * Working with [[other:​python:​jyp_steps#​netcdf_filesusing_cdms2_xarray_and_netcdf4|NetCDF]] files
  
-==== Sorting ====+ 
 +===== Using a configuration file ===== 
 + 
 +The built-in [[https://​docs.python.org/​3/​library/​configparser.html|configparser]] module can be easily used for reading (**and** writing!) text configuration files. 
 + 
 +Note: a configuration file is also a way to easily store and exchange text data ! 
 + 
 +===== Sorting ​=====
  
   * When dealing with **numerical values**, you should use the [[https://​numpy.org/​doc/​stable/​reference/​routines.sort.html|numpy sorting, searching, and counting routines]]!   * When dealing with **numerical values**, you should use the [[https://​numpy.org/​doc/​stable/​reference/​routines.sort.html|numpy sorting, searching, and counting routines]]!
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 ['​c',​ '​d',​ '​b',​ '​a'​]</​code>​ ['​c',​ '​d',​ '​b',​ '​a'​]</​code>​
  
-==== numpy related stuff ====+===== numpy related stuff =====
  
-=== Using a numpy array to store arbitrary objects ===+==== Using a numpy array to store arbitrary objects ​====
  
 The numpy arrays are usually used to store [[https://​numpy.org/​doc/​stable/​reference/​arrays.scalars.html|scalars]] of the same type (see also the [[https://​numpy.org/​doc/​stable/​reference/​arrays.dtypes.html|Data type objects (dtype)]]), very often numerical values. The numpy arrays are usually used to store [[https://​numpy.org/​doc/​stable/​reference/​arrays.scalars.html|scalars]] of the same type (see also the [[https://​numpy.org/​doc/​stable/​reference/​arrays.dtypes.html|Data type objects (dtype)]]), very often numerical values.
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        ​[<​cartopy.mpl.contour.GeoContourSet object at 0x2ab679e8bf10>,​        ​[<​cartopy.mpl.contour.GeoContourSet object at 0x2ab679e8bf10>,​
         None, None]], dtype=object)</​code>​         None, None]], dtype=object)</​code>​
 +
         ​         ​
-=== Dealing with a variable number of indices ===+==== Dealing with a variable number of indices ​====
  
 [[https://​numpy.org/​doc/​stable/​user/​basics.indexing.html#​dealing-with-variable-indices|Official reference]] [[https://​numpy.org/​doc/​stable/​user/​basics.indexing.html#​dealing-with-variable-indices|Official reference]]
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        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  1.]])</​code>​        [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  1.]])</​code>​
  
-=== Finding and counting unique values ===+ 
 +==== Finding and counting unique values ​====
  
 Use ''​np.unique'',​ do **not** try to use histogram related functions! Use ''​np.unique'',​ do **not** try to use histogram related functions!
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 array([1. , 1. , 1. , 1.5, 1.5, 1.5, 2. , 2. , 2. , 2. ])</​code>​ array([1. , 1. , 1. , 1.5, 1.5, 1.5, 2. , 2. , 2. , 2. ])</​code>​
  
-=== Applying a ufunc over all the elements of an array ===+ 
 +==== Applying a ufunc over all the elements of an array ====
  
 There are all sorts of //ufuncs// (Universal Functions), and we will just use below ''​add''​ from the [[https://​numpy.org/​doc/​stable/​reference/​ufuncs.html#​math-operations|math operations]],​ applied on the arrays defined in [[#​finding_and_counting_unique_values|Finding and counting unique values]] There are all sorts of //ufuncs// (Universal Functions), and we will just use below ''​add''​ from the [[https://​numpy.org/​doc/​stable/​reference/​ufuncs.html#​math-operations|math operations]],​ applied on the arrays defined in [[#​finding_and_counting_unique_values|Finding and counting unique values]]
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 (3.0, 4.5, 8.0)</​code>​ (3.0, 4.5, 8.0)</​code>​
  
-=== Applying a ufunc over specified sections of an array ===+ 
 +==== Applying a ufunc over specified sections of an array ====
  
 The [[https://​numpy.org/​doc/​stable/​reference/​generated/​numpy.ufunc.reduceat.html#​numpy.ufunc.reduceat|reduceat]] function can be used to avoid explicit python loops, and improve the speed (but not the readability...) of a script. The example below //​improves//​ what has been shown above The [[https://​numpy.org/​doc/​stable/​reference/​generated/​numpy.ufunc.reduceat.html#​numpy.ufunc.reduceat|reduceat]] function can be used to avoid explicit python loops, and improve the speed (but not the readability...) of a script. The example below //​improves//​ what has been shown above
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 >>>​ np.add.reduceat(np.sort(vals),​ slices_indices) >>>​ np.add.reduceat(np.sort(vals),​ slices_indices)
 array([3. , 4.5, 8. ])</​code>​ array([3. , 4.5, 8. ])</​code>​
 +
  
 /* /*
-==== Tip template ====+===== Tip template ​=====
  
 <​code>​Some code</​code>​ <​code>​Some code</​code>​
other/python/misc_by_jyp.txt · Last modified: 2024/04/19 12:02 by jypeter