code: def _load_common_err_data(self, common_err_data_path):
  		
  		common_err = {}
  
  		try:
  			with open(common_err_data_path, newline='') as f:
  				reader = csv.reader(f, delimiter='\t')
  				for line in reader:
  					if len(line) != 2:
  						continue
  
  					try:
  						assert line[0] not in common_err
  						assert all([char in self.ipa for char in line[1]])
  					except AssertionError:
  						raise IPADataError('Bad common IPA errors file')
  
  					common_err[line[0]] = line[1]
  
  		except (IOError, ValueError) as err:
  			self.log.error(str(err))
  			raise IPADataError('Could not open the common IPA errors data file')
  
  		return common_err
docs: Loads and returns the {bad: good} dictionary stored in the common
  		errors data file. Note that the dict's keys are single characters while
  		the values do not have to be. The method also asserts that all the
  		values are valid IPA strings.