Ah... "a sequence of only apostrophes [isn't valid]". I can exercise this constraint into my solution. Thanks :)

What language are you having trouble with? For Python, a word can have any amount of leading, trailing, or contained apostrophes, but important part is that it has to contain at least one letter. So a sequence of only apostrophes is not a valid word.

I remember also having problems with getting my implementation right.

For this input:
RdaPPuHQh.hqDUP'pwPI/;,/xgb??hqDUP'pwPI//sB'gmISoJE,vtttTxPDS,aHigIU,,..vtttTxPDS!?!SIexAyXprz ;;OhyFgnb'cC/:?!hqDUP'pwPI;RdaPPuHQh.!SIexAyXprz aXLHHhwU:sB'gmISoJE!,.hqDUP'pwPI.SIexAyXprz :aXLHHhwU/;:-SIexAyXprz!-! OhyFgnb'cC:-SEkXMJ.;:aHigIU?SIexAyXprz/-sB'gmISoJE,-, vtttTxPDS--aXLHHhwU:?!/SEkXMJ!//? aHigIU,:;:-'jxlpZOSdM;;sB'gmISoJE/.,hqDUP'pwPI aHigIU.xgb ;vtttTxPDS,SEkXMJ:?:SDAFdYqrk?SEkXMJ SDAFdYqrk/SEkXMJ;;/?xgb;?,SEkXMJ!:'jxlpZOSdM- /UCaIYcDkQ:;SDAFdYqrk ;SDAFdYqrk::UCaIYcDkQ- .UCaIYcDkQ-, RdaPPuHQh !'jxlpZOSdM.- ;sB'gmISoJE,OhyFgnb'cC,:;SEkXMJ;!;aXLHHhwU;? UCaIYcDkQ!,aHigIU/?RdaPPuHQh:;,,;aXLHHhwU..aXLHHhwU_OhyFgnb'cC? 'jxlpZOSdM,?:/,SDAFdYqrk -!-hqDUP'pwPI::/?SIexAyXprz-?'jxlpZOSdM?.;-RdaPPuHQh -SEkXMJ ;?:-RdaPPuHQh 'jxlpZOSdM;xgb:!? ,SEkXMJ-,/SDAFdYqrk/_;UCaIYcDkQ.aHigIU,!?OhyFgnb'cC !xgb_vtttTxPDS:;,sB'gmISoJE:-vtttTxPDS,/, !UCaIYcDkQ:;aHigIU;-.?'jxlpZOSdM,::'jxlpZOSdM'jxlpZOSdM-;//SDAFdYqrk!-! -SIexAyXprz- ;aHigIU.-/: SIexAyXprz?OhyFgnb'cC_ SEkXMJ-; --hqDUP'pwPI!: xgb;:-?:SDAFdYqrk; ;:,SDAFdYqrk/-SEkXMJ-OGzI:aXLHHhwU!.? ,SEkXMJ_;-!?OGzI SIexAyXprz!./SDAFdYqrk.,;sB'gmISoJE?-.;/SDAFdYqrk,aHigIU-!,,,xgb?sB'gmISoJE /xgb-aHigIU!-;aHigIU!.:,'jxlpZOSdM-,SDAFdYqrk.:aHigIU!hqDUP'pwPI! ??RdaPPuHQh.xgb-?;OhyFgnb'cC_SDAFdYqrk.xgb! --aHigIU??, vtttTxPDS,:!:SEkXMJ;./?RdaPPuHQh!!? hqDUP'pwPI-aXLHHhwU/:,;.aHigIU-?;,!SIexAyXprz-hqDUP'pwPI!;hqDUP'pwPI::,SDAFdYqrk!__,'jxlpZOSdM ?.!xgb!/:SDAFdYqrk-;/,sB'gmISoJE;.!!xgb!-?:hqDUP'pwPI:!SIexAyXprz;:::sB'gmISoJE_.!??SEkXMJ?!vtttTxPDS./:sB'gmISoJE:/OhyFgnb'cC_/'jxlpZOSdM/'jxlpZOSdM:SEkXMJ_!'jxlpZOSdM;-/! sB'gmISoJE;-aHigIU? :SIexAyXprz!-:;hqDUP'pwPI_.?OGzI ; ;aXLHHhwU- SEkXMJ:;!hqDUP'pwPI;.hqDUP'pwPI!:?:,'jxlpZOSdM.hqDUP'pwPI;/:?OhyFgnb'cC'jxlpZOSdM! !aHigIU;,,,sB'gmISoJE -;-SIexAyXprz;-.,aHigIU;hqDUP'pwPI?-,:aHigIU,!SIexAyXprz!,.,SEkXMJ/!/hqDUP'pwPI??OhyFgnb'cC-.-,SDAFdYqrk! 'jxlpZOSdM? OhyFgnb'cC 'jxlpZOSdM/hqDUP'pwPI SIexAyXprz;?aHigIU! sB'gmISoJE?/:SIexAyXprz : ?.aHigIU_...'jxlpZOSdM!::?.'jxlpZOSdM_, ?-RdaPPuHQh_;OhyFgnb'cC OhyFgnb'cC-.-? xgb_ ;.RdaPPuHQh?aHigIU;:OhyFgnb'cC/!:-SIexAyXprz?, !SIexAyXprz/'jxlpZOSdM.?;SDAFdYqrk/hqDUP'pwPI-aHigIU?..aHigIU,SEkXMJ//?OhyFgnb'cC_SIexAyXprz -SDAFdYqrk:/;'jxlpZOSdM,?/aHigIU?--/'jxlpZOSdM:-RdaPPuHQh/,hqDUP'pwPI-'jxlpZOSdM?!!, UCaIYcDkQ?.SEkXMJ!; xgb-aHigIU:///aHigIU!,;;,SIexAyXprz_??aHigIU?. SDAFdYqrk;SIexAyXprz.///'jxlpZOSdM-;xgb/ /'jxlpZOSdM_ !xgb/:/-:UCaIYcDkQ./SIexAyXprz _;SEkXMJ/RdaPPuHQh;

One possible output: ['ahigiu', "'jxlpzosdm", 'siexayxprz']

I think my code is failing because it doesn't acknolwedge a word having a leading apostrophe. But does a leading apostrophe satisfy the description of what a word is in this kata, in particular contradicting the meaning of "containing"? On a similar vein, glancing at the other test cases, I do not believe tailing apostrophes are included in the word. I can probably fix my code to include leading apostrophes, but how many? 1? 2? n? And can someone help clarify the definition of a word in this kata?

I like that you simply spelled out the sequence A through Z and did the string[i] in z. I could see doing this in other problems of similar nature.