glance.images.get inappropriate return

[Volodymyr Litovka]

Hello colleagues,

while working with glanceclient library, I faced an issue: when trying to find snapshot_id of the image, I'm calling glance.images.get and this call returns type of Image where block_devices_mapping property is type of 'Str', but with textual representation of List inside:

{
'container_format': 'bare',
'size': 0,
'block_device_mapping': '[{"guest_format": null, "boot_index": 0, "delete_on_termination": false, "no_device": null, "snapshot_id": "7fc78b3e-fa23-4710-914b-575ee0444c88", "device_name": "/dev/sda", "disk_bus": "scsi", "image_id": null, "source_type": "snapshot", "tag": null, "device_type": "disk", "volume_id": null, "destination_type": "volume", "volume_size": 10}]',
'locations': [{'url': 'swift+config://ref1/glance/35d2a539-0558-494a-92aa-85bdaf27caed', 'metadata': {}}], [ ... ] }

it looks strange since other properties are of different type (Integer (like 'size') or even List (like 'location')) and adds complexity to working with the result. It's better to have 'block_device_mappings' also type of List in order to work with natural Python data types like

image = glance.images.get(image_uuid)
for bd in image.block_device_mappings:
  if bd['boot_index'] == 0:
    snapshot_id = bd['snapshot_id']

So, the question is: is 'String' type of block_device_mapping bug or feature?

Thank you.

[Volodymyr Litovka (doka.ua)]

At the moment, such workaround is possible:

import ast

s = '[{"guest_format": null, "boot_index": 0, "delete_on_termination": false, "no_device": null, "snapshot_id": "7fc78b3e-fa23-4710-914b-575ee0444c88", "device_name": "/dev/sda", "disk_bus": "scsi", "image_id": null, "source_type": "snapshot", "tag": null, "device_type": "disk", "volume_id": null, "destination_type": "volume", "volume_size": 10}]'
s1 = s.replace('null', 'None').replace('true', 'True').replace('false', 'False')
bdm = ast.literal_eval(s1)
for bd in bdm:
    if bd['boot_index'] == 0:
        print(bd['snapshot_id'])

but such evaluation of result is very risky business.

[Abhishek Kekane (abhishek-kekane)]

Need more information on how to reproduce, detail steps would be good to have.