Python AWS Boto3: How do i read files from S3 Bucket?

+1 vote

Using Boto3, the python script downloads files from an S3 bucket to read them and write the contents of the downloaded files to a file called blank_file.txt.

What my question is, how would it work the same way once the script gets on an AWS Lambda function?

Aug 29, 2018 in AWS by datageek
• 2,440 points

11 answers to this question.

0 votes

AWS Lambda usually provides 512 MB of /tmp space. You can use that mount point to  store the downloaded S3 files or to create new ones. I have specified the command to do so below.

s3client.download_file(bucket_name, obj.key, '/tmp/'+filename) ... blank_file = open('/tmp/blank_file.txt', 'w')

The working directory used by Lambda is /var/task and it is a read-only filesystem. You will not be able to create files in it.

answered Aug 29, 2018 by Archana
• 4,090 points
0 votes

You can use the following code,

import boto3
s3 = boto3.resource('s3')
obj = s3.Object(bucketname, itemname)
body = obj.get()['Body'].read()
answered Dec 7, 2018 by Nitesh
What is itemname here?
As far as I know, the itemname here is the file that is being fetched and read by the function.
0 votes

You can download the file from S3 bucket 

import boto3
bucketname = 'my-bucket' # replace with your bucket name
filename = 'my_image_in_s3.jpg' # replace with your object key
s3 = boto3.resource('s3')
s3.Bucket(bucketname).download_file(filename, 'my_localimage.jpg')
answered Dec 7, 2018 by Jino
0 votes

Use this code to download the file.

import boto3
s3 = boto3.resource("s3")
k = Key(bucket,srcFileName)
answered Dec 7, 2018 by Nidhi
0 votes
s3 = boto3.resource('s3')
bucket = s3.Bucket('test-bucket')
for obj in bucket.objects.all():
    key = obj.key
    body = obj.get()['Body'].read()
answered Dec 10, 2018 by Saptdvip
0 votes

You can use data.Body.toString('ascii') to get the contents of the text file, assuming that the text file was encoded used ascii format.

answered Dec 10, 2018 by ramesh
0 votes

This is the code i found and can be used to read the file from S3 bucket using lambda function

def lambda_handler(event, context):
    # TODO implement
    import boto3

    s3 = boto3.client('s3')
    data = s3.get_object(Bucket='my_s3_bucket', Key='main.txt')
    contents = data['Body'].read()
answered Dec 10, 2018 by Shuvodip Ghosh
0 votes
I got a related article, I am not sure whether it works or not
answered Dec 10, 2018 by bugseeker
0 votes

You can use this function to read the file

exports.handler = (event, context, callback) => {
     var bucketName = process.env.bucketName;
     var keyName = event.Records[0].s3.object.key;
     readFile(bucketName, keyName, readFileContent, onError);

answered Dec 10, 2018 by Suresh Rao
0 votes
Here is a Amazon Documentation i found on web

This contains the code to do that.
answered Dec 10, 2018 by Girish
0 votes

All of the answers are kind of right, but no one is completely answering the specific question OP asked. I'm assuming that the output file is also being written to a 2nd S3 bucket since they are using lambda.  This code also uses an in-memory object to hold everything, so that needs to be considered:

import boto3

import io


inbucket = 'my-input-bucket'

outbucket = 'my-output-bucket'

s3 = boto3.resource('s3')

outfile = io.StringIO()

# Print out bucket names (optional)

for bucket in s3.buckets.all():


# Pull data from everyfile in the inbucket

bucket = s3.Bucket(inbucket)

for obj in bucket.objects.all():

  x = obj.get()['Body'].read().decode()


# Generate output file and close it!

outobj = s3.Object(outbucket,'outputfile.txt')



Check out "Amazon S3 Storage for SQL Server Databases" for setting up new Amazon S3 buckets

answered Mar 30 by awsdbaexpert
• 200 points

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