Exhaustive default_sort_key()
Exhaustive default_sort_key()

default_sort_key() now falls back to str() when it can't
figure out anything better, e.g.:

In [1]: sorted([None, {}, [], ()])
Out[1]: [None, {}, [], ()]

This helps a lot under Python 3.

ChristinaZografou/sympy,atsao72/sympy,hrashk/sympy,amitjamadagni/sympy,ChristinaZografou/sympy,wyom/sympy,ga7g08/sympy,abhiii5459/sympy,dqnykamp/sympy,chaffra/sympy,grevutiu-gabriel/sympy,sampadsaha5/sympy,lindsayad/sympy,debugger22/sympy,meghana1995/sympy,wanglongqi/sympy,Titan-C/sympy,abloomston/sympy,postvakje/sympy,saurabhjn76/sympy,AkademieOlympia/sympy,Curious72/sympy,Shaswat27/sympy,oliverlee/sympy,jamesblunt/sympy,debugger22/sympy,Davidjohnwilson/sympy,meghana1995/sympy,sunny94/temp,wanglongqi/sympy,diofant/diofant,jbbskinny/sympy,AunShiLord/sympy,ahhda/sympy,jamesblunt/sympy,kevalds51/sympy,hargup/sympy,shikil/sympy,rahuldan/sympy,yukoba/sympy,skirpichev/omg,hrashk/sympy,Mitchkoens/sympy,wanglongqi/sympy,jbbskinny/sympy,atsao72/sympy,sahilshekhawat/sympy,amitjamadagni/sympy,kmacinnis/sympy,maniteja123/sympy,sahilshekhawat/sympy,pbrady/sympy,aktech/sympy,saurabhjn76/sympy,yashsharan/sympy,moble/sympy,kaichogami/sympy,kumarkrishna/sympy,bukzor/sympy,skidzo/sympy,yashsharan/sympy,Gadal/sympy,moble/sympy,emon10005/sympy,sahmed95/sympy,AunShiLord/sympy,wyom/sympy,sampadsaha5/sympy,jerli/sympy,MridulS/sympy,vipulroxx/sympy,liangjiaxing/sympy,postvakje/sympy,chaffra/sympy,sunny94/temp,abhiii5459/sympy,Sumith1896/sympy,cswiercz/sympy,rahuldan/sympy,Vishluck/sympy,Titan-C/sympy,hrashk/sympy,meghana1995/sympy,beni55/sympy,MechCoder/sympy,AunShiLord/sympy,jbbskinny/sympy,saurabhjn76/sympy,VaibhavAgarwalVA/sympy,flacjacket/sympy,AkademieOlympia/sympy,garvitr/sympy,rahuldan/sympy,abloomston/sympy,maniteja123/sympy,moble/sympy,sampadsaha5/sympy,bukzor/sympy,maniteja123/sympy,VaibhavAgarwalVA/sympy,atsao72/sympy,ahhda/sympy,dqnykamp/sympy,drufat/sympy,beni55/sympy,pandeyadarsh/sympy,shipci/sympy,Davidjohnwilson/sympy,liangjiaxing/sympy,cccfran/sympy,kaichogami/sympy,yukoba/sympy,Sumith1896/sympy,ChristinaZografou/sympy,sahmed95/sympy,beni55/sympy,Gadal/sympy,shikil/sympy,mcdaniel67/sympy,madan96/sympy,cccfran/sympy,cswiercz/sympy,garvitr/sympy,Designist/sympy,kmacinnis/sympy,Curious72/sympy,chaffra/sympy,kaushik94/sympy,Arafatk/sympy,jaimahajan1997/sympy,asm666/sympy,wyom/sympy,hargup/sympy,toolforger/sympy,bukzor/sympy,kaichogami/sympy,farhaanbukhsh/sympy,skidzo/sympy,Designist/sympy,ahhda/sympy,Arafatk/sympy,srjoglekar246/sympy,souravsingh/sympy,kmacinnis/sympy,Vishluck/sympy,MechCoder/sympy,ga7g08/sympy,jaimahajan1997/sympy,sunny94/temp,shipci/sympy,asm666/sympy,madan96/sympy,cccfran/sympy,iamutkarshtiwari/sympy,sahilshekhawat/sympy,MridulS/sympy,lidavidm/sympy,jerli/sympy,pbrady/sympy,oliverlee/sympy,pandeyadarsh/sympy,Mitchkoens/sympy,yashsharan/sympy,grevutiu-gabriel/sympy,abloomston/sympy,lindsayad/sympy,aktech/sympy,garvitr/sympy,drufat/sympy,mcdaniel67/sympy,yukoba/sympy,kevalds51/sympy,pandeyadarsh/sympy,liangjiaxing/sympy,hargup/sympy,shipci/sympy,Designist/sympy,Titan-C/sympy,Vishluck/sympy,emon10005/sympy,mafiya69/sympy,drufat/sympy,atreyv/sympy,lidavidm/sympy,sahmed95/sympy,lidavidm/sympy,abhiii5459/sympy,madan96/sympy,kumarkrishna/sympy,mcdaniel67/sympy,toolforger/sympy,Shaswat27/sympy,jaimahajan1997/sympy,emon10005/sympy,iamutkarshtiwari/sympy,souravsingh/sympy,kevalds51/sympy,grevutiu-gabriel/sympy,MechCoder/sympy,Gadal/sympy,shikil/sympy,toolforger/sympy,souravsingh/sympy,postvakje/sympy,skidzo/sympy,Sumith1896/sympy,Arafatk/sympy,ga7g08/sympy,farhaanbukhsh/sympy,lindsayad/sympy,Shaswat27/sympy,atreyv/sympy,mafiya69/sympy,dqnykamp/sympy,aktech/sympy,AkademieOlympia/sympy,mafiya69/sympy,vipulroxx/sympy,atreyv/sympy,vipulroxx/sympy,debugger22/sympy,Curious72/sympy,asm666/sympy,MridulS/sympy,kumarkrishna/sympy,farhaanbukhsh/sympy,kaushik94/sympy,oliverlee/sympy,kaushik94/sympy,VaibhavAgarwalVA/sympy,jerli/sympy,cswiercz/sympy,Davidjohnwilson/sympy,iamutkarshtiwari/sympy,Mitchkoens/sympy,pbrady/sympy,jamesblunt/sympy