Python程序设计课件：Unicode与字符串（一）.ppt

Encoding（编码）一种简易的编码方式Thefirstencodingyoumightthinkofisanarrayof32-bitintegers.(2^32=4,294,967,296,whereastherangeofUnicodecodepointsisupto1,114,111)Inthisrepresentation,thestring“Python”wouldlooklikethis:一种简易的编码方式用32-bitinteger编码，有缺点：It’snotportable;differentprocessorsorderthebytesdifferently.It’sverywastefulofspace.Inmosttexts,themajorityofthecodepointsarelessthan127,orlessthan255,soalotofspaceisoccupiedbyzerobytes.It’snotcompatiblewithexistingCfunctionssuchasstrlen(),soanewfamilyofwidestringfunctionswouldneedtobeused.ManyInternetstandardsaredefinedintermsoftextualdata,andcan’thandlecontentwithembeddedzerobytes.解决方案思想：不要用固定长度的32-bitinteger（4bytes）。对常用的字符，给其一个小的编号（1byte），以节省空间；对不常用的字符，给其一个大编号一定要兼容已有的编码标准（ASCII）UTF-8isoneofthemostcommonlyusedencodings.UTFstandsfor“UnicodeTransformationFormat”,andthe“8”meansthat8-bitnumbersareusedintheencoding.UTF-8UTF-8usesthefollowingrules:Ifthecodepointis128,it’srepresentedbythecorrespondingbytevalue.Ifthecodepointisbetween128and0x7ff（十进制：2047）,it’sturnedintotwobytevaluesbetween128and255.Codepoints0x7ffareturnedintothree-orfour-bytesequences,whereeachbyteofthesequenceisbetween128and255.UTF-8UTF-8hasseveralconvenientproperties:ItcanhandleanyUnicodecodepoint.AUnicodestringisturnedintoastringofbytescontainingnoembeddedzerobytes.Thisavoidsbyte-orderingissues,andmeansUTF-8stringscanbeprocessedbyCfunctionssuchasstrcpy()andsentthroughprotocolsthatcan’thandlezerobytes.AstringofASCIItextisalsovalidUTF-8text.UTF-8isfairlycompact;themajorityofcodepointsareturnedintotwobytes,andvalueslessthan128occupyonlyasinglebyte.Unicode现状目前的Unicode字符分为17组编排，每组被称为平面（Plane），而每平面拥有65536个码位，共1,114,112个。目前只用了少数平面Unicode至今仍在不断增修，每个新版本都加入更多新的字符。目前必威体育精装版的版本为目