Basic encryption program

I got bored on a car ride yesterday, so I pulled out my laptop and wrote a python script that performs basic text file encryption. It still needs some work, but the algorithm is functional, and I was wondering what you guys thought of the strength of it. I know its definitely not full proof, but personally I think its pretty decent encryption. The script uses a 4 digit passcode system, but I think if you had the source code it would be pretty easy to make a bruteforcer that would run fairly fast. If someone is bored you can try to figure it out, but if nobody gets it, ill post the source code and then maybe someone could give me further evaluation.

Heres the result of a crypted text file:

markupL0v"OhjunV#pucA##xw]fx~nA#l{c@n)}jFv*\p&rynhRou#"Vr~)j>yn)uLpn)uRjpnuQlxwu]wx)o>nn)kQ#knvQh{)<f\w\v~q#)kAhj|A\q

Oh yeah, good idea.

Should I use different passcodes, though?

Okay, cya :)

Here are two more with the same passcode:

markupwqru]l|)oV#|neLqm)gUdvynB1)R"Eryn"Vr~)nFnn)kQ$\w\QL)~uBg)}jB#]JO##yjuPfxmg]kn{gi#jwf]vxvg]FJYU^\wJpA#g)vEd})y>v)j"OdwmqJ#}jdi#s~uQ#oxt]h"ygOlvnpQd}rqK#y~tMr|nuk\w

markupwqru]l|)oV#}qkOg)jpA#orp>o)nz>pyug]x|rpD#}qg]vjvg]sj|u@rmn0\qR)yLxum"Qk{xy]lw)uLpn)sRr}nu]ix{"Vr~5"?x})vEd}|"Pwrun]d)kwD#rw"J|)ytLj{jo]=1\pQkn#"Hlwmc]jurv@k)xwQ/)rv]gxnuKw)uqLn) gO|)jvQujlvFyn7\K

Then here's two more using completely different passcodes:

markupWkju2lv!w&lqh"s#fpo#ohun,#gjhxhufp'#sbu&freg3\qJ"'klom2L#trwooff2frnr~hwm{2zuppy#=)\!Lv!k'#fpo#ohug~|/!q%#fpo#ohun,B#Jo2xvjpy#d!y{hue"'hunk!do!h"qw-",rx!uwh/\p dnfu2lw!xwu|!e"qivu{qj!u"phuk hv/\!

markupWmnyPlx%{Dlsl&2#htsAojyrJ#inl7hwjtE#ufyDftikQ\sN&EknsqPL%xv6oqjjPftrv=hyq Pzwtt8#?-\?Lx%oE#htsAojyk=|1%uC#htsAojyrJB%NsPxxnt8#f%}:hwi&Ehwro?dq%l@qy1&Jrz%y6h1\t>dpjyPly%|6u~%i@qkzy:ql%y@pjyo>hx3\?\s\t

The last two use the exact same text file, just with different passcodes.