title: django change model form instance
body: <p>Is there any easy way to change the instance of a Django model form after it's been initialised?</p>
  
  <p>For example the following would pre-populate the form in a template with the contents currently in the db for the object with an id of 1:</p>
  
  <pre><code>form = exampleModelForm(instance = Model.objects.get(pk=1)
  </code></pre>
  
  <p>This will also save the relevant object when save() is called rather than create a new one.</p>
  
  <p>Where this will create a new object and not pre-populate the form in the template:</p>
  
  <pre><code>form = exampleModelForm()
  </code></pre>
  
  <p>As I'm returning a blank form from a different method, I would then like to assign an instance to it after it's been created and amend the object so that it can be saved and the template is pre-populate with the values that exist in the db. I want something like this but what I've tried doesn't seem to work:</p>
  
  <pre><code>form = methodThatGetsForm(somearg)
  form.instance = ExampleModel.objects.get(pk = getId(somearg))
  </code></pre>
  
  <p>Is there a simple function that I'm missing here?</p>