subleq.py

#Example program
prog = [ 21,  -1,  -2,  #0  #Print loc 21
         19,  20,  -1,  #3  #Subtract 1 from pos 20, quit when 0
         18,   0,  -2,  #6  #Add one to pos 0     
         17,  17,   0,  #9  #Jump to pos 0
          0,   0,   0,  #12
          0,   0,   0,  #15
         -1,   1,  13,  #18 Pos 20 is string length
         72, 101, 108,  #21 #Data begins here 
        108, 111,  32,
         87, 111, 114,
        108, 100,  33,
         10]

pc=0
c=0
out=""
while True:
    c+=1
    a,b,c=prog[pc:pc+3]
    if c==-2:
        c=pc+3
    pc+=3
    if b>=0:
        prog[b]-=prog[a]
        result=prog[b]
    else:
        result=-1
        if b==-1:
            out+= chr(prog[a])
    if result<=0:
        pc=c
    if pc<0:
        break
print(out)