if statement - Python if test condition fails when used with or

Question

Greetings python experts. I had written an if condition as follows that fails to be false for objects that should be false. I am writing in python 3.8.5. Note instance_list in this example contains a list of resources that are in various states. I only want to append vm_instance_list with resources that are not in a TERMINATED or TERMINATING state.

instance_results = compute_client.list_instances(
    compartment_id = compartment_id).data
vm_instance_list = []
for instance in instance_results:
    if instance.lifecycle_state != "TERMINATED" or instance.lifecycle_state != "TERMINATING:
        vm_instance_list.append(instance)

The above code appends vm_instance_list with every object in the list instance_results, aka each condition is interpreted as True for objects that are in a TERMINATED or TERMINATING lifecycle state. I have had to re-write to nest the if conditions, which works.

for instance in instance_results:
    if instance.lifecycle_state != "TERMINATED:
        if instance.lifecycle_state != "TERMINATING":
            vm_instance_list.append(instance)

I have no idea what why I have had to nest the above if statements and would appreciate if anyone could share some insights.

Thanks so much,

• Hank

question from:https://stackoverflow.com/questions/65948714/python-if-test-condition-fails-when-used-with-or

Answer 1

In your first version, the result is ALWAYS true, so every item is appended. Your second version is only true if both tests are true.

If you want the first version to behave like the second version, you need an 'and' statement, not an 'or'.