code: def ensure_single_char(func):
  	
  	@functools.wraps(func)
  	def wrapper(*args, **kwargs):
  		if not isinstance(args[0], str) or len(args[0]) != 1:
  			raise ValueError((
  				'This function should be invoked with a string of length one '
  				'as its first argument'))
  		return func(*args, **kwargs)
  
  	return wrapper
docs: Decorator that ensures that the first argument of the decorated function is
  	a single character, i.e. a string of length one.