title: How to find a capital letter words from an NLTK corpus using regex?
body: <p>I'd like to make a word list with a regular expression which is consists of all capital letters. 
  the data set is a bunch of biological theses text files called corpus. </p>
  
  <p>The result for <code>len(corpus.fileids())</code> is 487 which means that there are 487 theses in the corpus.</p>
  
  <p>The main reason for this is to collect word list to filter biological words like gene name and etc(ATP, BRCA)</p>
  
  <p>here are some codes that I've been trying. 
  (p.s. I'm using python3)</p>
  
  <p>I'm stuck with making functions to call out all files in the corpus.
  for a single file, I think this would work.</p>
  
  <pre><code>capital = re.findall(r'[A-Z]+', GNICorpus)
  </code></pre>
  
  <p>but the thing is that I have to go through all the words in the theses txt files in the corpus and have no idea. 
  1st trial</p>
  
  <pre><code>import re
  import nltk
  from nltk.corpus import*
  x = [
      (file)
      for file in Corpus.fileids() 
      for w in Corpus.words(file) 
      if w.upper()
  ]
  </code></pre>
  
  <p>2nd trial</p>
  
  <pre><code>   capital = re.findall(r'[A-Z]+', Corpus)
     capital
  </code></pre>
  
  <p>Third trial</p>
  
  <pre><code>for fileid in Corpus.fileids():
      words = Corpus.words(fileid)
      capital = re.findall(r'[A-Z]+', words)
  </code></pre>