title: How to declare a auto-incrementing alphanumerical id field with predefined aplphabetic part (Django python)
body: <p>I am developing an app in Django.</p>
  <p>I want to insert in my model an auto-incrementing alphanumerical ID field, having, by default, a fixed alphabetical part and an auto-incrementing numerical part.<br>
  But I also want the availability to change, from admin section, this id to another alphanumerical one, with a different alphanumerical and numerical part.<br>
  <strong>Please note:</strong> I don't want to overwrite the django default id field, I just want to include in my model a field that gets as default value an auto-incrementing alphanumerical value.</p>
  <p>Example of what I want:</p>
  <ul>
  <li><p>Desired alphabetical constant part: ITM</p>
  </li>
  <li><p>Desired numerical auto-incrementing part: 00000</p>
  <p>So that every object of my model, when generated, get default
  progressive values like: ITM00001, ITM00002, ITM00003, ...</p>
  </li>
  <li><p>Also, I would like to be able to change the field value from my admin
  section into values like ABC0000001, DFG0051, RST034, ...</p>
  </li>
  <li><p>Max field length: 10  (It can be also higher)</p>
  </li>
  </ul>
  <p>I realize that I have to use <code>AutoField</code> and to somehow join the constant string with the auto-incrementing numerical variable, but I don't know how to do it.</p>
  <pre><code>class my_model(models.Model):
  
      Field_1 = models.CharField(max_length=10, blank=True, null=True)
      static_ID = models.AutoField(???)
  </code></pre>
  <p>What code should I write to get a field with the features I described upwards?</p>