Question

str.swapcase()的Python文档说：

请注意s.swapcase().swapcase() == s。
并不一定正确

我猜这与Unicode有关;但是，在swapcase()的两次应用之后，我无法生成一个更改的字符串。什么样的字符串不能产生相同的结果？

这是我测试的（获得here）：

>>> testString = '''Bãｃｏл íｐѕüϻ Ꮷ߀ɭｏｒ ｓìｔ äｍéｔ ｑûìｓ àɭïɋüíｐ ｃüｌρä, ϻａｇｎâ èх ѕêԁ ѕｔｒíρ ｓｔêãｋ ｉл ԁò ｕｔ ｓåｌáｍí éхèｒｃìｔáｔïｏл ｐòｒƙ ɭ߀ｉｎ. Téԉԁëｒɭ߀íｎ ｔùｒｋèϒ ѕáûｓáɢè лùɭɭå ｐɑｒïáｔûｒ, ƃáｌｌ ｔíｐ âԁｉρïѕｉｃïԉǥ ɑᏧ ｃ߀ԉｓêｑｕäｔ ϻâｇлã ｖéлïｓｏл. Míлíｍ àｕｔë ѵ߀ɭüρｔåｔｅ ｍòɭɭíｔ ｔｒｉ-ｔíρ ｄèｓêｒùԉｔ. Oｃｃãèｃáｔ ｖëԉｉｓ߀ԉ êХ ｅｉùѕｍ߀ｄ ｓéᏧ ｌáｂｏｒüϻ ｐòｒƙ ｌòïл àｌｉɋûå ìлｃíԁìԁúԉｔ. Sｅｄ ｃòｍϻ߀Ꮷ߀ յｏɰｌ ｏｆｆíｃíä ｐòｒƙ ƅèɭｌｙ ｔéｍρòｒ ｌâƅòｒùϻ ｔâｉɭ ｓρåｒê ｒíｂｓ ｔｏлǥｕｅ ϻêáｔɭòáｆ ｍåɢｎä.

Kｉèɭｂàѕã ｉｎ ｃòлѕêｃｔêｔｕｒ ѵëлíàϻ ｐâｒíɑｔùｒ ｐ߀ｒｋ ɭ߀ｉｎ êｘêｒｃìｔâｔｉòл äｌìɋúíρ ｃâρｉｃｏｌɑ ρｏｒｋ ｔòлɢüê ｄüｉｓ ԁ߀ɭｏｒé ｒêｐｒéｈéԉᏧéｒïｔ. Tèｎԁèｒｌｏｉԉ ëх ｒèρｒéհｅԉԁéｒïｔ ｆûｇíãｔ äｄｉｐìｓｉｃｉԉｇ ｇｒ߀üｎᏧ ｒｏúлｄ, ƅａɭɭ ｔíｐ հàϻƃûｒǥèｒ ѕɦòùｌｄｅｒ ɭåｂ߀ｒûϻ ｔêｍρｏｒ ｒíƃêｙë. Eѕｓè ｈàϻ ѵëԉｉａｍ, åɭíɋùɑ ìｒüｒｅ ρòｒƙ ｃɦｏｐ ԁò ԁ߀ɭｏｒé ｆｒâｎｋｆüｒｔｅｒ ｎüｌｌａ ｐåｓｔｒäϻí ｓàｕｓàｇè ｓèᏧ. Eӽｃêｐｔêüｒ ѕëｄ ｔ-ｂ߀лë հɑϻ, ｅｓѕë ｕｔ ɭàƅｏｒíѕ ƃáｌｌ ｔíρ ｎｏｓｔｒúԁ ｓհ߀üｌｄêｒ ïｎ ｓｈòｒｔ ｒíƅｓ ρáｓｔｒáｍï. Eｓｓé ｈａｍƅûｒǥëｒ ɭäƅòｒé, ｆａｔƃàｃƙ ｔｅԉｄｅｒｌòïｎ ｓհ߀ｒｔ ｒïｂｓ ρｒòìｄéｎｔ ｒｉƅêｙｅ ɭａｂ߀ｒｕｍ. Nｕｌｌɑ ｔüｒԁùｃƙèｎ л߀ｎ, ｓρａｒè ｒìƅｓ ｅӽｃｅρｔｅｕｒ áｄïρìѕìｃïԉǥ êｔ ѕɦｏｒｔ ɭòｉｎ ｄｏｌｏｒë äｎïｍ ｄêѕêｒùлｔ. Sհäлƙｌè ｃúｐïԁäｔáｔ ｐｏｒｋ ｌòïｎ ｍéåｔｂäｌｌ, ԉ߀ｓｔｒｕｄ ｒéｐｒèհéԉԁêｒìｔ ɦɑϻｂｕｒǥêｒ ѕâɭɑϻí Ꮷｏｌ߀ｒè ɑｄ ｌêｂｅｒƙãｓ.

Bｏûｄｉл ｔｏлǥｕê ｃ߀ԉｓèｑûåｔ ｅà ｒüｍρ ƅáｌɭ ｔíρ ѕρâｒé ｒìｂѕ íｎ ｐｒòｉᏧｅｎｔ ｄûｉѕ ϻíлïｍ èíｕѕｍòᏧ ｃ߀ｒԉêᏧ ƃèèｆ ƅɑｃ߀л ｄ߀ｌｏｒè. Cｏｒｎèｄ ƅëèｆ ｄｒûｍｓｔｉｃƙ ｃùｌｐａ, éлïｍ ｂａɭɭ ｔìｐ ϻéａｔｂâｌɭ ｌａｂ߀ｒê ｔｒｉ-ｔïｐ ｖëｎｉｓｏԉ ǥｒｏùԉԁ ｒòùлԁ հɑｍ ｉл èä ｂãｃòｎ. Eѕѕé ìᏧ ѕúԉｔ, ｓհｏùｌｄéｒ ƙïｅɭƃäѕà ãԁｉρｉｓïｃïԉɢ ɦａϻｂûｒｇêｒ úｔ ԁòɭ߀ｒｅ ｆåｔｂäｃƙ ԁ߀ɭòｒ äлïｍ ｔｒï-ｔíｐ. EíùｓϻòᏧ ｎüｌɭã ｌäｂòｒｕϻ лíѕｉ êｘｃéｐｔèúｒ. Oｃｃåéｃåｔ Ꮷüíѕ ԁèｓｅｒüлｔ ｔｏԉǥｕｅ ϳ߀ｗɭ. Rèρｒéɦëԉԁêｒｉｔ áɭïｑúíｐ ｆûǥｉàｔ ｔùｒｋｅｙ ｖéｎｉãϻ ｑüìѕ.'''
>>> testString.swapcase().swapcase() == testString
True

Answer 1

当多个字母是同一个字母的小写字母时就是这种情况。

例如，微字符µ (U+00B5)和mu字符μ (U+03BC)：

>>> u'\xb5'.swapcase()
u'\u039c'
>>> u'\u03bc'.swapcase()
u'\u039c'

这两个是不同的字符，但它们的大写字母是相同的。这意味着当应用str.swapcase()时，它们会返回相同的字符。但是，再次执行此操作不能（也不会）返回两个字母。

>>> u'\xb5'.swapcase().swapcase()
u'\u03bc'

Answer 2

虽然Volatility提出了将大写mu和大写微解析为同一Unicode码点的示例，但另一个有趣的情况是，应用swapcase两次导致不同的答案：

>>> 'ß'.swapcase().swapcase()
'ss'

困惑？德语辅音ß（发音为[s]）在SS一次应用后变为swapcase，然后在第二次应用后变为ss。

这里是他们的整个列表（→代表一个swapcase）：

µ (0xb5) → Μ (0x39c) → μ (0x3bc) → Μ (0x39c)
ß (0xdf) → SS (0x5353) → ss (0x7373) → SS (0x5353)
İ (0x130) → i̇ (0x69307) → İ (0x49307) → i̇ (0x69307)
ı (0x131) → I (0x49) → i (0x69) → I (0x49)
ŉ (0x149) → ʼN (0x2bc4e) → ʼn (0x2bc6e) → ʼN (0x2bc4e)
ſ (0x17f) → S (0x53) → s (0x73) → S (0x53)
ǰ (0x1f0) → J̌ (0x4a30c) → ǰ (0x6a30c) → J̌ (0x4a30c)
ͅ (0x345) → Ι (0x399) → ι (0x3b9) → Ι (0x399)
ΐ (0x390) → Ϊ́ (0x399308301) → ΐ (0x3b9308301) → Ϊ́ (0x399308301)
ΰ (0x3b0) → Ϋ́ (0x3a5308301) → ΰ (0x3c5308301) → Ϋ́ (0x3a5308301)
ς (0x3c2) → Σ (0x3a3) → σ (0x3c3) → Σ (0x3a3)
ϐ (0x3d0) → Β (0x392) → β (0x3b2) → Β (0x392)
ϑ (0x3d1) → Θ (0x398) → θ (0x3b8) → Θ (0x398)
ϕ (0x3d5) → Φ (0x3a6) → φ (0x3c6) → Φ (0x3a6)
ϖ (0x3d6) → Π (0x3a0) → π (0x3c0) → Π (0x3a0)
ϰ (0x3f0) → Κ (0x39a) → κ (0x3ba) → Κ (0x39a)
ϱ (0x3f1) → Ρ (0x3a1) → ρ (0x3c1) → Ρ (0x3a1)
ϴ (0x3f4) → θ (0x3b8) → Θ (0x398) → θ (0x3b8)
ϵ (0x3f5) → Ε (0x395) → ε (0x3b5) → Ε (0x395)
և (0x587) → ԵՒ (0x535552) → եւ (0x565582) → ԵՒ (0x535552)
ẖ (0x1e96) → H̱ (0x48331) → ẖ (0x68331) → H̱ (0x48331)
ẗ (0x1e97) → T̈ (0x54308) → ẗ (0x74308) → T̈ (0x54308)
ẘ (0x1e98) → W̊ (0x5730a) → ẘ (0x7730a) → W̊ (0x5730a)
ẙ (0x1e99) → Y̊ (0x5930a) → ẙ (0x7930a) → Y̊ (0x5930a)
ẚ (0x1e9a) → Aʾ (0x412be) → aʾ (0x612be) → Aʾ (0x412be)
ẛ (0x1e9b) → Ṡ (0x1e60) → ṡ (0x1e61) → Ṡ (0x1e60)
ẞ (0x1e9e) → ß (0xdf) → SS (0x5353) → ss (0x7373) → SS (0x5353)
ὐ (0x1f50) → Υ̓ (0x3a5313) → ὐ (0x3c5313) → Υ̓ (0x3a5313)
ὒ (0x1f52) → Υ̓̀ (0x3a5313300) → ὒ (0x3c5313300) → Υ̓̀ (0x3a5313300)
ὔ (0x1f54) → Υ̓́ (0x3a5313301) → ὔ (0x3c5313301) → Υ̓́ (0x3a5313301)
ὖ (0x1f56) → Υ̓͂ (0x3a5313342) → ὖ (0x3c5313342) → Υ̓͂ (0x3a5313342)
ᾀ (0x1f80) → ἈΙ (0x1f08399) → ἀι (0x1f003b9) → ἈΙ (0x1f08399)
ᾁ (0x1f81) → ἉΙ (0x1f09399) → ἁι (0x1f013b9) → ἉΙ (0x1f09399)
ᾂ (0x1f82) → ἊΙ (0x1f0a399) → ἂι (0x1f023b9) → ἊΙ (0x1f0a399)
ᾃ (0x1f83) → ἋΙ (0x1f0b399) → ἃι (0x1f033b9) → ἋΙ (0x1f0b399)
ᾄ (0x1f84) → ἌΙ (0x1f0c399) → ἄι (0x1f043b9) → ἌΙ (0x1f0c399)
ᾅ (0x1f85) → ἍΙ (0x1f0d399) → ἅι (0x1f053b9) → ἍΙ (0x1f0d399)
ᾆ (0x1f86) → ἎΙ (0x1f0e399) → ἆι (0x1f063b9) → ἎΙ (0x1f0e399)
ᾇ (0x1f87) → ἏΙ (0x1f0f399) → ἇι (0x1f073b9) → ἏΙ (0x1f0f399)
ᾐ (0x1f90) → ἨΙ (0x1f28399) → ἠι (0x1f203b9) → ἨΙ (0x1f28399)
ᾑ (0x1f91) → ἩΙ (0x1f29399) → ἡι (0x1f213b9) → ἩΙ (0x1f29399)
ᾒ (0x1f92) → ἪΙ (0x1f2a399) → ἢι (0x1f223b9) → ἪΙ (0x1f2a399)
ᾓ (0x1f93) → ἫΙ (0x1f2b399) → ἣι (0x1f233b9) → ἫΙ (0x1f2b399)
ᾔ (0x1f94) → ἬΙ (0x1f2c399) → ἤι (0x1f243b9) → ἬΙ (0x1f2c399)
ᾕ (0x1f95) → ἭΙ (0x1f2d399) → ἥι (0x1f253b9) → ἭΙ (0x1f2d399)
ᾖ (0x1f96) → ἮΙ (0x1f2e399) → ἦι (0x1f263b9) → ἮΙ (0x1f2e399)
ᾗ (0x1f97) → ἯΙ (0x1f2f399) → ἧι (0x1f273b9) → ἯΙ (0x1f2f399)
ᾠ (0x1fa0) → ὨΙ (0x1f68399) → ὠι (0x1f603b9) → ὨΙ (0x1f68399)
ᾡ (0x1fa1) → ὩΙ (0x1f69399) → ὡι (0x1f613b9) → ὩΙ (0x1f69399)
ᾢ (0x1fa2) → ὪΙ (0x1f6a399) → ὢι (0x1f623b9) → ὪΙ (0x1f6a399)
ᾣ (0x1fa3) → ὫΙ (0x1f6b399) → ὣι (0x1f633b9) → ὫΙ (0x1f6b399)
ᾤ (0x1fa4) → ὬΙ (0x1f6c399) → ὤι (0x1f643b9) → ὬΙ (0x1f6c399)
ᾥ (0x1fa5) → ὭΙ (0x1f6d399) → ὥι (0x1f653b9) → ὭΙ (0x1f6d399)
ᾦ (0x1fa6) → ὮΙ (0x1f6e399) → ὦι (0x1f663b9) → ὮΙ (0x1f6e399)
ᾧ (0x1fa7) → ὯΙ (0x1f6f399) → ὧι (0x1f673b9) → ὯΙ (0x1f6f399)
ᾲ (0x1fb2) → ᾺΙ (0x1fba399) → ὰι (0x1f703b9) → ᾺΙ (0x1fba399)
ᾳ (0x1fb3) → ΑΙ (0x391399) → αι (0x3b13b9) → ΑΙ (0x391399)
ᾴ (0x1fb4) → ΆΙ (0x386399) → άι (0x3ac3b9) → ΆΙ (0x386399)
ᾶ (0x1fb6) → Α͂ (0x391342) → ᾶ (0x3b1342) → Α͂ (0x391342)
ᾷ (0x1fb7) → Α͂Ι (0x391342399) → ᾶι (0x3b13423b9) → Α͂Ι (0x391342399)
ι (0x1fbe) → Ι (0x399) → ι (0x3b9) → Ι (0x399)
ῂ (0x1fc2) → ῊΙ (0x1fca399) → ὴι (0x1f743b9) → ῊΙ (0x1fca399)
ῃ (0x1fc3) → ΗΙ (0x397399) → ηι (0x3b73b9) → ΗΙ (0x397399)
ῄ (0x1fc4) → ΉΙ (0x389399) → ήι (0x3ae3b9) → ΉΙ (0x389399)
ῆ (0x1fc6) → Η͂ (0x397342) → ῆ (0x3b7342) → Η͂ (0x397342)
ῇ (0x1fc7) → Η͂Ι (0x397342399) → ῆι (0x3b73423b9) → Η͂Ι (0x397342399)
ῒ (0x1fd2) → Ϊ̀ (0x399308300) → ῒ (0x3b9308300) → Ϊ̀ (0x399308300)
ΐ (0x1fd3) → Ϊ́ (0x399308301) → ΐ (0x3b9308301) → Ϊ́ (0x399308301)
ῖ (0x1fd6) → Ι͂ (0x399342) → ῖ (0x3b9342) → Ι͂ (0x399342)
ῗ (0x1fd7) → Ϊ͂ (0x399308342) → ῗ (0x3b9308342) → Ϊ͂ (0x399308342)
ῢ (0x1fe2) → Ϋ̀ (0x3a5308300) → ῢ (0x3c5308300) → Ϋ̀ (0x3a5308300)
ΰ (0x1fe3) → Ϋ́ (0x3a5308301) → ΰ (0x3c5308301) → Ϋ́ (0x3a5308301)
ῤ (0x1fe4) → Ρ̓ (0x3a1313) → ῤ (0x3c1313) → Ρ̓ (0x3a1313)
ῦ (0x1fe6) → Υ͂ (0x3a5342) → ῦ (0x3c5342) → Υ͂ (0x3a5342)
ῧ (0x1fe7) → Ϋ͂ (0x3a5308342) → ῧ (0x3c5308342) → Ϋ͂ (0x3a5308342)
ῲ (0x1ff2) → ῺΙ (0x1ffa399) → ὼι (0x1f7c3b9) → ῺΙ (0x1ffa399)
ῳ (0x1ff3) → ΩΙ (0x3a9399) → ωι (0x3c93b9) → ΩΙ (0x3a9399)
ῴ (0x1ff4) → ΏΙ (0x38f399) → ώι (0x3ce3b9) → ΏΙ (0x38f399)
ῶ (0x1ff6) → Ω͂ (0x3a9342) → ῶ (0x3c9342) → Ω͂ (0x3a9342)
ῷ (0x1ff7) → Ω͂Ι (0x3a9342399) → ῶι (0x3c93423b9) → Ω͂Ι (0x3a9342399)
Ω (0x2126) → ω (0x3c9) → Ω (0x3a9) → ω (0x3c9)
K (0x212a) → k (0x6b) → K (0x4b) → k (0x6b)
Å (0x212b) → å (0xe5) → Å (0xc5) → å (0xe5)
ﬀ (0xfb00) → FF (0x4646) → ff (0x6666) → FF (0x4646)
ﬁ (0xfb01) → FI (0x4649) → fi (0x6669) → FI (0x4649)
ﬂ (0xfb02) → FL (0x464c) → fl (0x666c) → FL (0x464c)
ﬃ (0xfb03) → FFI (0x464649) → ffi (0x666669) → FFI (0x464649)
ﬄ (0xfb04) → FFL (0x46464c) → ffl (0x66666c) → FFL (0x46464c)
ﬅ (0xfb05) → ST (0x5354) → st (0x7374) → ST (0x5354)
ﬆ (0xfb06) → ST (0x5354) → st (0x7374) → ST (0x5354)
ﬓ (0xfb13) → ՄՆ (0x544546) → մն (0x574576) → ՄՆ (0x544546)
ﬔ (0xfb14) → ՄԵ (0x544535) → մե (0x574565) → ՄԵ (0x544535)
ﬕ (0xfb15) → ՄԻ (0x54453b) → մի (0x57456b) → ՄԻ (0x54453b)
ﬖ (0xfb16) → ՎՆ (0x54e546) → վն (0x57e576) → ՎՆ (0x54e546)
ﬗ (0xfb17) → ՄԽ (0x54453d) → մխ (0x57456d) → ՄԽ (0x54453d)

Answer 3

我试过这个

v = lambda x: x.swapcase().swapcase() == x
[unichr(x) for x in range(10000) if not v(unichr(x))]

结果如下：

[u'\xb5', u'\u0130', u'\u0131', u'\u017f', u'\u03c2', u'\u03d0', u'\u03d1', u'\u03d5', u'\u03d6', u'\u03f0', u'\u03f1', u'\u03f4', u'\u03f5', u'\u1e9b', u'\u1e9e', u'\u1f80', u'\u1f81', u'\u1f82', u'\u1f83', u'\u1f84', u'\u1f85', u'\u1f86', u'\u1f87', u'\u1f90', u'\u1f91', u'\u1f92', u'\u1f93', u'\u1f94', u'\u1f95', u'\u1f96', u'\u1f97', u'\u1fa0', u'\u1fa1', u'\u1fa2', u'\u1fa3', u'\u1fa4', u'\u1fa5', u'\u1fa6', u'\u1fa7', u'\u1fb3', u'\u1fbe', u'\u1fc3', u'\u1ff3', u'\u2126', u'\u212a', u'\u212b']

何时使用swapcase两次不返回相同的答案？

3 个答案: