Vorlesung 3 Nerlich

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Archivierte Version vom 2021-04-11T15:45:47+00:00. Aktuelle Version

S.9

#/usr/bin/env python3

from random import Random


class WordGenerator:
	"""docstring for WordGenerator"""
	def __init__(self, alphabet: set):
		if not alphabet.isdisjoint({None}):
			raise ValueError("The alphabet cannot contain None")
		
		self._alphabet = frozenset(alphabet)
		self._generator = Random()
		self._word = ""
		self._ended = False
		
	def __iter__(self):
		return self
		
	def __next__(self):
		result = self._generator.choice(tuple(self._alphabet.union({None})))
		if result is None or self._ended:
			self._ended = True
			raise StopIteration()
		else:
			self._word = self._word + result
			return result
		
	@property
	def alphabet(self) -> frozenset:
		return self._alphabet
	
	@property
	def word(self):
		while not self._ended:
			try:
				next(self)
			except StopIteration:
				pass
		return self._word
		
	def next(self):
		return self.__next__()
		
	def reset(self):
		self._word = ""
		self._ended = False


def chi_length_3(w: WordGenerator):  # requires at most 4 checks
	for n in range(1,4):
		try:
			
			print("Letter #{} is '{}'".format(n, next(w)))  # up to 3 checks, determining lengths 0 to 2
			
		except StopIteration:
			print("Word '{}' is of length shorter than 3!".format(w.word))
			return False
	try:
		
		print("Letter #{} is '{}'".format(n, next(w)))  # fourth check shows whether of length 3
		
		print("Word '{}' is of length longer than 3!".format(w.word))
		return False
	except StopIteration:
		print("Word '{}' is of length 3.".format(w.word))
		return True

def chi_starts_with_letter(w: WordGenerator, letter):  # always requires only one check
	try:
		
		result = next(w)  # one check
		
		print("Letter #1 is '{}'".format(result))
		if result == letter:
			print("Word '{}' starts with '{}'!".format(w.word, letter))
			return True
		else:
			print("Word '{}' does not start with '{}'.".format(w.word, letter))
			return False
	except StopIteration:
		print("Word '{}' does not start at all.".format(w.word))
		return False


A = {'a', 'b'}

chi_length_3(WordGenerator(A))

chi_starts_with_letter(WordGenerator(A), 'a')

Vorlesung 3 Nerlich

S.9

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