      "def list_of_chars(chars):\n",
      "    if chars is None:\n",
      "        return None\n",
      "    size = len(chars)\n",
      "    for i in xrange(size/2):\n",
      "        chars[i], chars[size-1-i] = \\\n",
      "            chars[size-1-i], chars[i]\n",
      "    return chars"
     ]
    },
 
</s> remove     "    for _ in xrange(n):\n",
 </s> add     "    for _ in range(n):\n", </s> remove     "    for i in xrange(1, cycles+1):\n",
 </s> add     "    for i in range(1, cycles+1):\n", </s> remove     "    for l in xrange(lower, upper + 1):\n",
    "        for u in xrange(lower, upper + 1):\n",
 </s> add     "    for l in range(lower, upper + 1):\n",
    "        for u in range(lower, upper + 1):\n", </s> remove     "    for i in xrange(start + 1, len(data)):\n",
 </s> add     "    for i in range(start + 1, len(data)):\n", </s> remove     "        for _ in xrange(0, iterations_to_compare_half):\n",
 </s> add     "        for _ in range(0, iterations_to_compare_half):\n",
    "    for i in range(size/2):\n",
      "def list_of_chars(chars):\n",
      "    if chars is None:\n",
      "        return None\n",
      "    size = len(chars)\n",
    "    for i in range(size/2):\n",
      "        chars[i], chars[size-1-i] = \\\n",
      "            chars[size-1-i], chars[i]\n",
      "    return chars"
     ]
    },
keep keep keep keep replace keep keep keep keep keep
 Changed xrange to range to be compatible with Python 3. 
arrays_strings/reverse_string/reverse_string_solution.ipynb