How To Read And Overwrite A File In Aws S3 Using Lambda And Python?

I believe you have created an event Trigger on S3 and associated it with Lambda and when you are replacing the file you get the lambda triggered and it becomes a loop.

There could be 2 ways to handle it:

1.Configure a PUT OR POST event type ( which ever suits your case) to trigger the lambda. Now save the updated file at another location and then copy it to the original one. Doing this s3 will generate a "S3:ObjectCreated:Copy" event which will not invoke the Lambda again.

 # Copying file from secondary location to original location
 copy_sr = {
        "Bucket":bucket,
        "Key"   :file_key_copy
        
    }
    
    s3_resource.meta.client.copy(copy_sr, 
    final_bucket,file_key_copy
    )
    
    #Deleting the file from the secondary location
    s3_client.delete_object(Bucket=bucket,
    Key=file_key_copy
    ) 

2.Use SQS queue and configure it not to precess any message received twice in a specified period of time ( depending on the frequency of file getting updated)