How to Retrieve Subfolder Names in an S3 Bucket Using Boto3

Accessing and managing objects in AWS S3 using Boto3 can simplify various cloud storage tasks. If you need to retrieve subfolder names within a specific directory in an S3 bucket, using the correct Boto3 methods is key. Here’s how to efficiently extract these subfolder names without wading through every individual object.

Understanding S3 Object Storage

AWS S3 is essentially an object storage service where files, images, and even folders (subfolders) are stored as objects with key-value pairs. When working with S3, it’s crucial to understand that “folders” and “subfolders” are merely a UI representation. S3 doesn’t have a traditional filesystem hierarchy. Each object is stored with a unique key that can simulate directory paths.

Setting Up Your Environment

Ensure you have Boto3 and AWS credentials configured. You can do this using the AWS CLI or by setting environment variables for AWS access key and secret key.

1. Install Boto3:

   pip install boto3
   

2. Configure AWS Credentials:

   Use the AWS CLI to configure credentials or manually create a file ~/.aws/credentials with your AWS access key and secret key.

Retrieving Subfolder Names

To retrieve subfolder names, you need to list objects in your S3 bucket and leverage the Delimiter and Prefix parameters effectively. Here’s how:

import boto3

# Initialize the S3 client and specify your bucket and prefix.
client = boto3.client('s3')
bucket_name = 'my-bucket'
prefix = 'first-level/'  # Important: end with a slash.

# List objects using the delimiter to separate folders.
response = client.list_objects_v2(Bucket=bucket_name, Prefix=prefix, Delimiter='/')

if 'CommonPrefixes' in response:
    for common_prefix in response['CommonPrefixes']:
        subfolder = common_prefix['Prefix']
        # Display each subfolder within the specified prefix.
        print(f'Subfolder: {subfolder}')
else:
    print("No subfolders found.")

Key Considerations

• Prefix: Define this to specify the directory level beneath which you want the subfolder names. Ensure it ends with a forward slash (/), which distinguishes it as a directory.

• Delimiter: Set this to '/' in order to retrieve objects grouped by the common path prefix.

Explanation:
The list_objects_v2 call with a Delimiter returns a hierarchy of objects. By setting a delimiter, you can make it return a list of directories (or prefixes) instead of individual files. This allows you to avoid unnecessary retrieval of all third-level objects when you simply need the second-level directory names.

Additional Resources

For further exploration, including handling paginated results or dealing with complex key naming schemes, refer to the Boto3 documentation for list_objects_v2.