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• The Windows and Unix versions of the program could be combined very easily. Most of the differences are simply how you build pathnames. But you don’t have to do it differently: just always use the os.path* functions, or simply use the / separator everywhere, it works under Windows just fine.
   
• If there are genuine platform differences that you must handle, put them in their separate files (like windows.py and unix.py), then detect the platform and import the correct file (import <platform> as foo, then call foo.bar(...)).
   
• In addition, the Windows and Unix versions seem to do slightly different things. The Unix version does not have a menu, uses different names for different configuration items (the whole config_handler class), and even has bugs (Unix filesystems DO have maximum filename lengths, you need to handle output_long_filenames on the Unix side too). It seems to me that the Windows version is more recent?
   
• The program could be split into several smaller programs that each do one thing. One downloads by search query, one downloads by range, and so on. The common parts of them should be put in a file that gets imported in each program. Currently some of the tools (sort_dl_list, find_duplicates, etc.) already import derpibooru_dl, so this shouldn’t be a terribly hard thing to do. Plus, small programs would also adhere to the Unix philosophy better :-)
   
• There should be a database of sorts that stores past downloads and allows you to rerun those queries. The program should keep track of multiple unfinished download jobs and offer me a chance to continue/abort any of them. Instead of relying separate files to store the download status, you could consider using a real database, like SQLite, to keep track of everything. This would make the program more robust: no million JSON files needed. If you use SQLite, one could use any of the several sqlite admin tools to manipulate the database if needed.
   
• The “press Enter to close window” is useless when running from the command line.
   
  The filename length limit is a real problem in all systems. It’s impossible to cram everything in there, no matter what. One idea is to prioritize the tags, like always having the artist name plus the rating, and then adding as many tags as you can fit.

1. rating (safe, questionable, suggestive, explicit, gotesque, grimdark)  
2. artist  
3. ponies pictured
    
   Here is a set of ponies I’ve complied from some image tagged with ‘everypony’:  
   ponies = set("ambrosia,angel bunny,apple bloom,apple strudel,applejack,aunt orange,babs seed,berry punch,big macintosh,blinkie pie,bon bon,braeburn,breezie,bulk biceps,button mash,care package,carrot cake,cerberus,cheerilee,cheese sandwich,chief thunderhooves,cindy block,cloudchaser,cloudy quartz,clyde pie,coco pommel,cookie crumbles,cup cake,daisy,daisy jo,daring do,derpy hooves,diamond tiara,discord,dj pon-3,doctor caballeron,doctor whooves,donut joe,dumbbell,featherweight,filthy rich,flam,flash sentry,fleetfoot,fleur-de-lis,flim,flitter,flower wishes,fluttershy,gilda,gizmo,granny smith,gummy,gustave le grande,harry,hoity toity,hondo flanks,hoops,horse md,hugh jelly,hydra,igneous rock,inkie pie,irma,iron will,king sombra,lightning dust,lily,lily valley,limestone pie,little strongheart, lucy packard,lutece twins,lyra,mane goodall,marble pie,maud pie,mayor mare,morton saltworthy,mr breezy,mr. waddle,mr. zippy,ms. harshwhinny,mulia mild,night light,nurse redheart,nurse sweetheart,octavia,opalescence,owlowiscious,pearl,photo finish,pie,pinkie pie,pipsqueak,poindexter,post haste,pound cake,prim hemline,prince blueblood,princess cadance,princess celestia,princess luna,princess twilight,pumpkin cake,queen chrysalis,rainbow dash,rarity,robert lutece,rosalind lutece,roseluck,rover,royal guard,rumble,sapphire shores,scootaloo,screw loose,seabreeze,sheriff silverstar,shining armor,silver shill,silver spoon,snails,snips,snowflake,soarin',spike,spitfire,spot,stormwalker,sue pie,sunset shimmer,suri polomare,sweetie belle,sweetie drops,sweetiecorn,tank,trenderhoof,trixie, truffle shuffle,twilight sparkle,twilight velvet,twist,vinyl scratch,wild fire,wings,winona,zecora,zippoorwhill".split(","))

@PrinceCadance
Sorry to hear you’re having problems.
I plan to write more API key debug code when my main comp is back online.
(Showing the first and last few letters of the key while keeping the middle secret, for example)
Until then, I’ve got a few questions that might help fix this.

Could you tell me what program you’re using to edit the settings file?

Do the first and last characters of the key in the settings file the same as on the site? You may have accidentally missed one at the end.
Keys are supposed to be fixed in length based on what the site admins have said. If the checks say yours is 19 this is a likely cause.

Does the key have a single space between it and the equals sign, like “api_key = KEYKEYKEY”?
(I don’t know if it matters, but it might. I can’t check if it does right now)

I’ve just finished updating my script to be easier to use, please try it and tell me if there is anything you find difficult.
(Except the text only stuff, I don’t have the time to learn to make fancy graphical interfaces)
The problem with downloading the .exe version should be fixed.

https://github.com/woodenphone/Derpibooru-dl