title: Define a custom Python exception mirroring the builtin exception format
body: <p>First of all, here are similar questions that address this problem:<br>
      1. <a href="https://stackoverflow.com/questions/6410764/raising-exceptions-without-raise-in-the-traceback">Raising exceptions without &#39;raise&#39; in the traceback?</a><br>
      2. <a href="https://stackoverflow.com/questions/4419785/dont-show-python-raise-line-in-the-exception-stack">Don&#39;t show Python raise-line in the exception stack</a></p>
  
  <p>No, it is not a duplicate, as the answers don't actually solve the problem.</p>
  
  <p>I don't want to format the actual <code>traceback</code> object. Instead, I want to just format the way it is displayed to the user.</p>
  
  <h1>The Code</h1>
  
  <h3>source.py</h3>
  
  <pre><code>class HelloError(Exception):
      pass
  
  def type_hello_here(string):
      if string != 'hello':
          raise HelloError("You must type 'hello', not '{}'".format(string))
  </code></pre>
  
  <h3>script.py</h3>
  
  <pre><code>from source import type_hello_here
  type_hello_here('hello') # No error here
  type_hello_here('booty') # Obviously returns an error because booty != hello
  </code></pre>
  
  <h1>The Bad Exception</h1>
  
  <pre><code>Traceback (most recent call last):
    File "D:/python/script.py", line 3, in &lt;module&gt;
      type_hello_here('booty')
    File "D:\python\source.py", line 6, in type_hello_here
      raise HelloError("You must type 'hello', not '{}'".format(string))
  source.HelloError: You must type 'hello', not 'booty'
  </code></pre>
  
  <h1>The Desired Exception</h1>
  
  <pre><code>Traceback (most recent call last):
    File "D:/python/script.py", line 3, in &lt;module&gt;
      type_hello_here('booty')
  HelloError: You must type 'hello', not 'booty'
  </code></pre>
  
  <p>I want to format it in such a way that the last entry, pointing to the code in the source module is not displayed, as the <strong><em>error does not actually occur there</em></strong>. Also, I want the source in '<em>source</em>.HelloError' to disappear.</p>