code: def prefix(self, length=1):
      if self.pointer + length >= len(self.buffer):
          self.update(length)
      return self.buffer[self.pointer : self.pointer + length]
  
file_path: keepsake/python/keepsake/_vendor/yaml/reader.py
imports: from .error import YAMLError, Mark
  import codecs, re
label_desc: Use image node_id 3 for calling the Reader obj's underlying member method code with example usage: obj.prefix(length) and returns: self