other:python:misc_by_jyp
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other:python:misc_by_jyp [2022/12/12 13:50] jypeter Improved by changing the sections' levels |
other:python:misc_by_jyp [2023/04/27 09:47] jypeter [Data representation] Improved |
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| <code>sys.exit('Some optional message about why we are stopping')</code> | <code>sys.exit('Some optional message about why we are stopping')</code> | ||
| + | ===== Data representation ===== | ||
| + | A few notes for a future section or page about about data representation (bits and bytes) on disk and in memory, vs data format | ||
| + | |||
| + | * Binary data representation of some numbers: | ||
| + | * [[https://en.wikipedia.org/wiki/Integer_(computer_science)|Integers]] | ||
| + | * Range: | ||
| + | * 4-byte integers (''numpy.int32''): −2,147,483,648 to 2,147,483,647 | ||
| + | * 8-byte integers (''numpy.int64''): −9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 | ||
| + | * Note: using [[https://en.wikipedia.org/wiki/Two%27s_complement|two's complement]] for negative integers | ||
| + | * [[https://en.wikipedia.org/wiki/IEEE_754|Floating point numbers]] (//IEEE 754// standard aka //IEEE Standard for Binary Floating-Point for Arithmetic//) | ||
| + | * Range: | ||
| + | * 4-byte float (''numpy.float32''): ~8 significant digits * 10E±38 | ||
| + | * See also [[https://en.wikipedia.org/wiki/Single-precision_floating-point_format|Single-precision floating-point format|Single-precision floating-point format]] | ||
| + | * 8-byte float (''numpy.float64''): ~15 significant digits * 10E±308 | ||
| + | * Special values: | ||
| + | * [[https://en.wikipedia.org/wiki/NaN|NaN]] (''numpy.nan''): //Not a Number// | ||
| + | * Infinity (''-numpy.inf'' and ''numpy.inf'') | ||
| + | * [[https://en.wikipedia.org/wiki/Bit_numbering|Bit numbering]] | ||
| + | * [[https://en.wikipedia.org/wiki/Endianness|Endianness]] | ||
| + | |||
| + | * Array addressing | ||
| + | |||
| + | * disk and ram usage: how to check the usage (available ram and disk), best practice on multi-user systems (how much allowed?) | ||
| + | * ''du'', ''df'', ''cat /proc/meminfo'', ''top'' | ||
| + | |||
| + | * understanding and reverse-engineering //binary// format | ||
| + | * ''od'', ''strings'' | ||
| + | |||
| + | * binary vs text format: ascii, utf, raw | ||
| + | * text related functions in python: ''str'', ''int'', ''float'', ''ord'', ... | ||
| + | * lists conversion with ''map'' and ''join'' | ||
| + | |||
| + | * Misc : ''md5sum'' | ||
| ===== Checking if a file/directory is writable by the current user ===== | ===== Checking if a file/directory is writable by the current user ===== | ||
| Line 43: | Line 76: | ||
| ===== Playing with strings ===== | ===== 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]] | ||
| - | ==== Splitting strings ==== | + | ==== Splitting (complex) 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 | ||
| Line 257: | Line 287: | ||
| Note: a configuration file is also a way to easily store and exchange text data ! | Note: a configuration file is also a way to easily store and exchange text data ! | ||
| + | |||
| + | ===== Working with global variables ===== | ||
| + | |||
| + | There is a good chance you don't actually want/need a //global// variable. Be sure to use the ''global'' statement correctly if you want to avoid side-effects... | ||
| + | |||
| + | * [[https://docs.python.org/3/faq/programming.html?highlight=global#why-am-i-getting-an-unboundlocalerror-when-the-variable-has-a-value|Using (and changing) a global variable inside a script or module]] | ||
| + | * Simple module example\\ <code>_myvar = 10 | ||
| + | |||
| + | def set_myvar(new_val): | ||
| + | # Note: need to explicitly define a global variable (of a module) | ||
| + | # as 'global' BEFORE changing its value in a function! | ||
| + | # Otherwise, the value will not be REdefined outside the function | ||
| + | global _myvar | ||
| + | _myvar = new_val | ||
| + | |||
| + | def get_myvar(): | ||
| + | return _myvar | ||
| + | |||
| + | def myfunc(nb_repeat = 10): | ||
| + | print(nb_repeat * _myvar)</code> | ||
| + | * [[https://docs.python.org/3/faq/programming.html?highlight=global#how-do-i-share-global-variables-across-modules|Sharing global variables across modules]] | ||
| ===== Sorting ===== | ===== Sorting ===== | ||
| Line 435: | Line 486: | ||
| >>> 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> | ||
| + | |||
| + | |||
| + | ===== matplotlib related stuff ===== | ||
| + | |||
| + | ==== Working with time axes (and ticks) ==== | ||
| + | |||
| + | If you have problems setting the limits of a time axis, choosing the ticks' locations, or specifying the style of the labels, you should check the: | ||
| + | * [[https://matplotlib.org/stable/gallery/index.html#ticks|Ticks examples' gallery]] | ||
| + | * [[https://matplotlib.org/stable/gallery/text_labels_and_annotations/date.html|Date tick labels example]] | ||
other/python/misc_by_jyp.txt · Last modified: 2024/04/19 12:02 by jypeter
