old_contents: import collections
  
  _DATA = {}
  _HISTORY = []
  
  
  def register(path, value):
    if path in _DATA:
      raise KeyError('%s already specified' % path)
    _DATA[path] = value
  
  def get(path):
    value = _DATA[path]
    if callable(value):
      _DATA[path] = value()
    return _DATA[path]
  
  
  def init(register_base=True):
    if _DATA:
      raise Exception('Already initialized')
    _DATA['initialized'] = True
    if register_base:
      register('/letter/frequency', _get_letter_frequency)
  
  def reset():
    _DATA.clear()
  
  
  def save():
    global _DATA
    _HISTORY.append(_DATA)
    _DATA = {}
  
  
  def restore():
    global _DATA
    _DATA = _HISTORY.pop()
  
  
  def _get_letter_frequency():
    return collections.OrderedDict(sorted(list(zip('abcdefghijklmnopqrstuvwxyz', [
      # abcdef.
      9081174698, 419765694, 596623239, 361493758, 593086170, 297285731,
      # ghijkl.
      227771642, 220523502, 3086225277, 180739802, 195647953, 252900442,
      341583838, 437961375, 246429812, 303249898, 139563801, 323534251,  # mnopqr.
      565123981, 388448018, 179615587, 204486977, 252231566, 508609523,  # stuvwx.
      195011703, 132095202,  # yz.
    ])), key=lambda x: x[1], reverse=True))
  
new_contents: import collections
  import time
  
  _DATA = {}
  _HISTORY = []
  _DEADLINE_MS = 10
  
  
  def register(path, value):
    if path in _DATA:
      raise KeyError('%s already specified' % path)
    _DATA[path] = value
  
  
  def get(path):
    value = _DATA[path]
    if callable(value):
      start = time.time()
      _DATA[path] = value()
      delta = (time.time() - start) * 1000
      if delta > _DATA['_DEADLINE_MS']:
        raise Exception('Deadline exceeded loading %s (%.0f ms)' % (path, delta))
    return _DATA[path]
  
  
  def init(register_base=True):
    if _DATA:
      raise Exception('Already initialized')
    _DATA['_INITIALIZED'] = True
    _DATA['_DEADLINE_MS'] = _DEADLINE_MS
    if register_base:
      register('/letter/frequency', _get_letter_frequency)
  
  
  def reset():
    _DATA.clear()
  
  
  def save():
    global _DATA
    _HISTORY.append(_DATA)
    _DATA = {}
  
  
  def restore():
    global _DATA
    _DATA = _HISTORY.pop()
  
  
  def _get_letter_frequency():
    return collections.OrderedDict(sorted(list(zip('abcdefghijklmnopqrstuvwxyz', [
      # abcdef.
      9081174698, 419765694, 596623239, 361493758, 593086170, 297285731,
      # ghijkl.
      227771642, 220523502, 3086225277, 180739802, 195647953, 252900442,
      341583838, 437961375, 246429812, 303249898, 139563801, 323534251,  # mnopqr.
      565123981, 388448018, 179615587, 204486977, 252231566, 508609523,  # stuvwx.
      195011703, 132095202,  # yz.
    ])), key=lambda x: x[1], reverse=True))
  
subject: Raise error if fetching something from warehouse takes 10+ms.