class_docstr: A concrete implementation of the Corpus class using the NLTK library.
  Downloads and works with NLTK-supported corpora.
  
  Args:
      nltk_corpus (str): The name of the NLTK corpus to download and use.
code: def __init__(self, nltk_corpus: str) -> None:
      self.nltk_corpus = nltk_corpus
      nltk.download(self.nltk_corpus)
      nltk.download("averaged_perceptron_tagger")
      super().__init__(name=self.nltk_corpus)
      self.freq_dist_cache = None
      self.pos_tagged_words_cache = None
  
imports: from abc import ABC, abstractmethod
  from typing import Dict, Iterator, List, Tuple
  import nltk
label_desc: Use image node_id 1 to create a new NltkCorpus object from inherited base classes: Corpus with example: obj = NltkCorpus(nltk_corpus)