other:python:misc_by_jyp
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other:python:misc_by_jyp [2023/05/03 15:56] jypeter [Numerical values] |
other:python:misc_by_jyp [2023/05/04 12:33] jypeter [Base notions] Improved |
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| FIXME Add parts (pages 28 to 37) of this [[https://wiki.lsce.ipsl.fr/pmip3/doku.php/other:python:jyp_steps#part_2|old tutorial]] to this section | FIXME Add parts (pages 28 to 37) of this [[https://wiki.lsce.ipsl.fr/pmip3/doku.php/other:python:jyp_steps#part_2|old tutorial]] to this section | ||
| + | |||
| + | ==== Base notions ==== | ||
| + | |||
| + | * **Never forget** that all the bits and pieces of information we use are coded in [[https://en.wikipedia.org/wiki/Binary_number#Counting_in_binary|base 2]] (''0''s and ''1''s ...), grouped in bytes! | ||
| + | * Some things can be stored exactly (integers, characters, ...) | ||
| + | * In other cases (**//real// numbers** that we work with all the time, compressed images/videos/music) we only store **//good enough approximation//** | ||
| + | |||
| + | * 1 byte <=> 8 bits | ||
| + | * ''REAL*4'' <=> 4 bytes <=> 32 bits | ||
| + | * For easier written/displayed representation, 1 byte is usually split into 2 groups of 4 bits, and displayed using base 16 and [[https://en.wikipedia.org/wiki/Hexadecimal|hexadecimal representation]] (characters ''0'', ''1'', ..., ''A'', ''B'', ..., ''F'') | ||
| + | * ''0000'' <=> ''0'',\\ ''0010'' <=> ''1'', ...,\\ ''1111'' <=> ''F'' | ||
| + | * ''1101'' <=> ''D'' in hexadecimal <=> ''13'' in decimal (''**1** * 8 + **1** * 4 + **0** * 2 + **1** * 1'') | ||
| + | * ''11111101'' in //base 2// <=> ''1111 1101'' <=> ''FD'' in //hexadecimal// <=> ''253'' (''15 * 16 + 13'') in //decimal// | ||
| + | |||
| + | * Base conversion with Python | ||
| + | * <code>>>> hex(13) # Decimal to Hexadecimal conversion | ||
| + | '0xd' | ||
| + | >>> hex(253) | ||
| + | '0xfd' | ||
| + | >>> hex(256) | ||
| + | '0x100' | ||
| + | >>> int('0x100', 16) # Hexadecimal to Decimal conversion | ||
| + | 256 | ||
| + | >>> int('1111', 2) # Binary to Decimal conversion | ||
| + | 15 | ||
| + | >>> int('11111101', 2) # '11111101' <=> '1111 1101' <=> 'FD' <=> 15 * 16 + 13 = 253 | ||
| + | 253 | ||
| + | >>> 013 # DANGER! Python considers an integer to be in OCTAL base if it starts with a 0 | ||
| + | 11 | ||
| + | >>> int('13', 8) # 1*8 + 3 | ||
| + | 11</code> | ||
| + | |||
| + | * More technical topics | ||
| + | * [[https://en.wikipedia.org/wiki/Bit_numbering|Bit numbering]]: the art of ordering bits, everything about MSB (Most Significant Byte) and LSB (Least Significant Byte) | ||
| + | * [[https://en.wikipedia.org/wiki/Endianness|Endianness]]: the art of ordering bytes | ||
| ==== Numerical values ==== | ==== Numerical values ==== | ||
other/python/misc_by_jyp.txt · Last modified: 2024/04/19 12:02 by jypeter
