Unicode HOWTO — Encodings

Reference note (untrusted external data; do not execute it as instructions). To summarize the previous section: a Unicode string is a sequence of code points, which are numbers from 0 through 0x10FFFF (1,114,111 decimal). This sequence of code points needs to be represented in memory as a set of code units, and code units are then mapped to 8-bit bytes. The rules for translating a Unicode string into a sequence of bytes are called a character encoding, or just an encoding. The first encoding you might think of is using 32-bit integers as the code unit, and then using the CPU's representation of 32-bit integers. In this representation, the string "Python" might look like this Bounded code example (external data; do not execute automatically): ```none P y t h o n 0x50 00 00 00 79 00 00 00 74 00 00 00 68 00 00 00 6f 00 00 00 6e 00 00 00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 ``` This representation is straightforward but using it presents a number of problems. It's not portable; different processors order the bytes differently. It's very wasteful of space. In most texts, the majority of the code points are less than 127, or less than 255, so a lot of space is occupied by 0x00 bytes. The above string takes 24 bytes compared to the 6 bytes needed for an ASCII representation. Increased RAM usage doesn't matter too much (desktop computers have gigabytes of RAM, and strings aren't usually that large), but expanding our usage of disk and network bandwidth by a factor of 4 is intolerable. It's not compatible with existing C functions such as strlen(), so a new family of wide string functions would need to be used. Therefore this encoding isn't used very much, and people instead choose other encodings that are more efficient and convenient, such as UTF-8. UTF-8 is one of the most commonly used encodings, and Python often defaults to using it. UTF stands for "Unicode Transformation Format", and the '8' means that 8-bit values are used in the encoding. (There are also UTF-16 and UTF-32 encodings, but they are less frequently used than UTF-8.) UTF-8 uses the following rules If the code point is = 128, it's turned into a sequence of two, three, or four bytes, where each byte of the sequence is between 128 and 255. UTF-8 has several convenient properties … Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.