old_contents: 
  SINGLE_BIT_MASK =  [1 << x for x in range(7, -1, -1)]
  
  class BitString(object):
  
  	def __init__(self, bytes, length=None, offset=None):
  		self.bytes = bytes
  		self.offset = offset if offset is not None else 0
  		self.length = length if length is not None else 8 * len(data) - self.offset 
  
  
  	def __getitem__(self, key):
  		try:
  			start = key.start
  			stop = key.stop
  		except AttributeError:
  			if key < 0 or key >= length:
  				raise IndexError()
  			byte_index, bit_offset = divmod(self.offset + key), 8)
  			return self.bytes[byte_index] & SINGLE_BIT_MASK[bit_offset]
  
new_contents: 
  SINGLE_BIT_MASK =  [1 << x for x in range(7, -1, -1)]
  
  class BitString(object):
  
  	def __init__(self, bytes, length=None, offset=None):
  		self.bytes = bytes
  		self.offset = offset if offset is not None else 0
  		self.length = length if length is not None else 8 * len(data) - self.offset 
  
  
  	def __getitem__(self, key):
  		try:
  			start = key.start
  			stop = key.stop
  		except AttributeError:
  			if key < 0 or key >= length:
  				raise IndexError()
  			byte_index, bit_offset = (divmod(self.offset + key), 8)
  			return self.bytes[byte_index] & SINGLE_BIT_MASK[bit_offset]
  
subject: Add closing paren to tuple expression