old_contents: #!/usr/bin/env python
  #encoding: utf-8
  
  '''
  @author: Chris Hokamp
  @contact: chris.hokamp@gmail.com
  '''
  
  
  # this only finds the first instance of the token in the sentence (see the idx= keyword arg of the extract_window function)
  def locate_token(token, sentence):
      try:
          i = sentence.index(token)
          return i
      except ValueError:
          return -1
  
  
  # window_size is the window on both left and right of the token of interest
  def extract_window(token_list, token, window_size=1, with_token=True, idx=None):
      index = idx or locate_token(token, token_list)
      if index != -1:
          if with_token:
              context_args = [token_list, token, window_size, index]
              window = left_context(*context_args) + [token] + right_context(*context_args)
              return window
          else:
              context_args = [token_list, token, window_size, index]
              window = left_context(*context_args) + right_context(*context_args)
              return window
      return None
  
  
  def left_context(token_list, token, context_size=1, idx=None):
      index = idx or locate_token(token, token_list)
      left_window = []
      if index != -1:
          for i in range(index-context_size, index):
              if i < 0:
                  left_window.append('_START_')
              else:
                  left_window.append(token_list[i])
      return left_window
  
  
  def right_context(token_list, token, context_size=1, idx=None):
      index = idx or locate_token(token, token_list)
      right_window = []
      if index != -1:
          for i in range(index+1, index+context_size+1):
              if i > len(token_list)-1:
                  right_window.append('_END_')
              else:
                  right_window.append(token_list[i])
      return right_window
  
  
new_contents: #!/usr/bin/env python
  #encoding: utf-8
  
  '''
  @author: Chris Hokamp
  @contact: chris.hokamp@gmail.com
  '''
  
  
  # this only finds the first instance of the token in the sentence (see the idx= keyword arg of the extract_window function)
  def locate_token(token, sentence):
      try:
          i = sentence.index(token)
          return i
      except ValueError:
          return -1
  
  
  # window_size is the window on both left and right of the token of interest
  def extract_window(token_list, token, window_size=1, with_token=True, idx=None):
      index = idx or locate_token(token, token_list)
      if index != -1:
          if with_token:
              context_args = [token_list, token, window_size, index]
              window = left_context(*context_args) + [token] + right_context(*context_args)
              return window
          else:
              context_args = [token_list, token, window_size, index]
              window = left_context(*context_args) + right_context(*context_args)
              return window
      return None
  
  
  def left_context(token_list, token, context_size=1, idx=None):
      index = idx or locate_token(token, token_list)
      left_window = []
      if index != -1:
          for i in range(index-context_size, index):
              if i < 0:
  #                left_window.append('_START_')
                  left_window.append('<s>')
              else:
                  left_window.append(token_list[i])
      return left_window
  
  
  def right_context(token_list, token, context_size=1, idx=None):
      index = idx or locate_token(token, token_list)
      right_window = []
      if index != -1:
          for i in range(index+1, index+context_size+1):
              if i > len(token_list)-1:
  #                right_window.append('_END_')
                  right_window.append('</s>')
              else:
                  right_window.append(token_list[i])
      return right_window
  
  
subject: replace '_START_' with <s>