title: Find all extensions in a directory and order them alphabetically
body: <p>I've got a homework which I am unable to solve :(</p>
  
  <p>I have to use <code>os</code> and <code>os.path</code>.</p>
  
  <ol>
  <li><p>I have to write a program which asks you for a directory but if you don't input anything the directory is current working directory, then it prints all file's extensions ordered alphabetically.</p>
  
  <p>The program should work like that:</p>
  
  <p>Directory:  <code>/Users/Andrew/Desktop</code></p>
  
  <pre><code>.ai
  .docx
  .jpg
  .png
  .py
  .rar
  .zip
  </code></pre></li>
  <li><p>I have to write a program which again asks you for a directory but if you don't input anything the directory is current working directory, then it prints all file's extensions ordered alphabetically but this time it should draw a line for every filetype and list the files with appropriate extension.</p>
  
  <p>Directory:  <code>/Users/Andrew/Desktop</code></p>
  
  <pre><code>.ai
  ----------
  cat.ai
  
  .docx
  ----------
  Job application.docx
  
  .png
  ----------
  Screen Shot1.png
  Untitled-1.png
  
  .py
  ----------
  1.py
  2.py
  4.py
  5.py
  6.py
  
  .xls
  ----------
  PlanB.xls
  Tommorow.xls
  </code></pre></li>
  </ol>
  
  <p>Your help would be appreciated.</p>
  
  <p>This is my attempt at solving first problem:</p>
  
  <pre><code>import os
  
  directory=input("Directory:")
  
  if directory:
      files=os.listdir(directory)
  else:
      files=os.listdir(os.getcwd())
  
  
  for filetypes in files:
      print(os.path.splitext(filetypes)[1])
  </code></pre>
  
  <p>I finally did the first assignment, but I can't solve the second one. I'd really need help.</p>
  
  <p>Thank you</p>