How to Check if an Object Exists in AWS S3 Using Python and Boto3

By Birtchum Thompson | April 5, 2020

It is often necessary to programmatically check if an object exists before performing an action such as deleting the object, updating, the object, or invalidating an AWS CloudFront object. This tutorial will demonstrate how to check if an object exists in an S3 bucket using Python and Boto3.

Boto3, AWS’s Python SDK, does not provide a straight-forward method of doing this, but a simple HEAD request for the object will reveal if it exists or not. If the object does not exist in the S3 bucket, a ClientError will be raised and the response will contain a 404 error code. The following script will return True if the object exists, return False if it receives the 404 error code, or return the error code if something else went wrong.

import boto3
from botocore.exceptions import ClientError

def exists_in_bucket(s3_key):
    bucket = 'some-bucket-name'
    s3 = boto3.client('s3')

    try:
        s3.head_object(Bucket=bucket, Key=s3_key)
        return True
    
    except ClientError as e:
        error_code = int(e.response['Error']['Code'])
        
        if error_code == 404:
            return False
        
        else:
            return error_code

    except Exception as e:
        return int(e.response['Error']['Code'])

if __name__ == '__main__':
    print(exists_in_bucket('some/file.json'))

Python