NOTE: organism.py belongs in a directory "breeder"

organism.py

#!/usr/bin/env python
import ast
from os.path import isfile
from hashlib import md5
from random import randint, choice
from glob import glob
import re

# scratch area
"""
"abcdefghijklmnopqrstuvwxyz1234567890+=-_~`{}[]\|';:,\\!@#$%^&*()"
"abcdefghijklmnopqrstuvwxyz1234567890+=-_~`{}[]\|';:,\\!@#$%^&*()"
"abcdefghijklmnopqrstuvwxyz1234567890+=-_~`{}[]\|';:,\\!@#$%^&*()"
False True None
"""

# random index
r = lambda codes: randint(0, len(codes) - 1)

get_code = lambda f: open(f, 'r').read()
choose_mate = lambda: choice(glob("./*.py"))

def swap(codes, a, b):
    codes[a], codes[b] = codes[b], codes[a]

splits = (
    (lambda code: (list(code), '',)),
    (lambda code: (code.split(' '), ' ',)),
    (lambda code: (code.split('\n'), '\n',)),
    (lambda code: (code.split('    '), '    ',)),
    (lambda code: (code.split('\n    '), '\n    ',)),
)
    
mutators = (
    (lambda codes: codes.insert(r(codes), choice(codes))),
    (lambda codes: codes.insert(r(codes), choice(codes))),
    (lambda codes: swap(codes, r(codes), r(codes))),
    (lambda codes: swap(codes, r(codes), r(codes))),
    (lambda codes: codes.pop(r(codes))),
)    
    
def mutate(code_str):
    splitter = choice(splits)
    mutator = choice(mutators)
    
    codes, joiner = splitter(code_str)
    mutator(codes)

    return joiner.join(codes) or code_str
    
def combine_code(code1, code2):
    code1 = code1.split("\n")
    code2 = code2.split("\n")
    
    out_len = max([len(code1), len(code2)])
    
    out = []
    for i in range(out_len):
        code = [code1, code2][i % 2]
        out += code[i:i+1]
            
    return '\n'.join(out)

for _ in range(50):
    # breed
    child_code = get_code(__file__)
    child_code = combine_code(child_code, get_code(choose_mate()))

    child_code = mutate(child_code)
    child_code = mutate(child_code)
    child_code = mutate(child_code)
    
    try: ast.parse(child_code)
    except SyntaxError: continue

    child_name = "./{}.py".format(md5(child_code).hexdigest())
    if not isfile(child_name):
        with open(child_name, 'w') as f:
            f.write(child_code)

predator.py

#!/usr/bin/env python

from glob import glob
import os
from os.path import getsize
import random

def get_free_space_mb():
    st = os.statvfs('/')
    return st.f_bavail * st.f_frsize / 1024 / 1024.0

orgs = glob("./*.py")
random.shuffle(orgs)

big_files = iter(sorted(orgs, key=getsize, reverse=True))
all_files = iter(orgs)

killed = 0
while get_free_space_mb() < (5 * 1024):
    try:
        os.unlink(big_files.next())
        killed += 1
        os.unlink(all_files.next())
        killed += 1
    except OSError:
        pass

if killed:
    print "killed {0} big organisms".format(killed)

runner.sh

#!/bin/bash

cd ./breeder

while true; do 
  f=$(python -c "import glob, random; print(random.choice(glob.glob('./*.py')))");

  python "$f" 2> /dev/null;
  if [[ $? != 0 ]]; then
    rm "$f";
    echo -n '.'
  else
    echo
    echo "$f"
  fi
  
  python ../predator.py
done