title: How to find instances that DONT have a tag using Boto3
body: <p>I'm trying to find instances that DONT have a certain tag.</p>
  
  <p>For instance I want all instances that don't have the Foo tag.
  I also want instances that don't have the Foo value equal to Bar.</p>
  
  <p>This is what I'm doing now:</p>
  
  <pre><code>import boto3
  
  
  def aws_get_instances_by_name(name):
      """Get EC2 instances by name"""
      ec2 = boto3.resource('ec2')
  
      instance_iterator = ec2.instances.filter(
          Filters=[
              {
                  'Name': 'tag:Name',
                  'Values': [
                      name,
                  ]
              },
              {
                  'Name': 'tag:Foo',
                  'Values': [
  
                  ]
              },
          ]
      )
  
      return instance_iterator
  </code></pre>
  
  <p>This is returning nothing.</p>
  
  <p>What is the correct way?</p>