Difference between blob and get_blob in Google Cloud Storage's Python library

The similarity and difference between the methods blob(~) and get_blob(~) in Google Cloud Storage (GCS)'s Python client library are as follows:

• blob(~) and get_blob(~) both return a Blob object.

• the main difference between blob(~) and get_blob(~) is that, blob(~) does not actually send any request to GCS, while get_blob(~) fetches meta-information about the blob from GCS. There are two main implications of this:

  • calling blob('cat.png') will not send a request to GCS so we are not sure if this file actually exists on GCS. On the other hand, calling get_blob('cat.png') will send a request to GCS to fetch the meta-information of the cat.png. If the cat.png does not exist, then None is returned.

  • meta-information (e.g. size) is available only to blob objects fetched by get_blob(~) but not by blob(~):

    from google.cloud import storage

    
    

    # Authenticate ourselves using the primary key of the service account

    path_to_private_key = './gcs-project-354207-099ef6796af6.json'

    client = storage.Client.from_service_account_json(json_credentials_path=path_to_private_key)

    
    

    bucket = storage.Bucket(client, 'example-bucket-skytowner')

    blob = bucket.get_blob('cat.png')

    print(f'[get_blob] {blob.size} bytes')

    
    

    blob = bucket.blob('cat.png')

    print(f'[blob] {blob.size} bytes')

    [get_blob] 160546 bytes

    [blob] None bytes

    Here, notice how blob.size returns None when we use the blob(~) constructor. Also, to learn how to generate the primary key of a service account, please consult our guide here.