Amazon S3 Archives - Page 2 of 2

How to write Python string to a file in S3 Bucket using boto3

To write a file from a Python string directly to an S3 bucket we need to use the boto3 package.

There are 2 ways to write a file in S3 using boto3. The first is via the boto3 client, and the second is via the boto3 resource. Both of these methods will be shown below.

S3 objects and keys

If you are new to AWS S3, you might be confused with some of the terms. So we’ll define some of them here. If you already know what objects and keys are then you can skip this section.

S3 objects are the same as files. When we run the method put_object what it means is that we are putting a file into S3.

S3 keys are the same as the filename with its full path. So if we want to create an object in S3 with the name of filename.txt within the foobar folder then the key is foobar/filename.txt.

Now that we have clarified some of the AWS S3 terms, follow the details below to start writing Python strings directly to objects in S3.

How to generate S3 presigned URL using boto3 and Python

If you want to give your users temporary access to a private S3 file without giving them access to the AWS console, you will need to generate an S3 presigned URL of your target file.

To generate and test the S3 presigned URL, you can try the code below.

How to read a JSON file in S3 and store it in a Dictionary using boto3 and Python

If you want to get a JSON file from an S3 Bucket and load it into a Python Dictionary then you can use the example codes below.

There are 4 scenarios for the examples scripts below.

AWS boto3 provides 2 ways to access S3 files, the boto3.client('s3') and boto3.resource('s3'). For each of the example scenarios above, a code will be provided for the two methods.

Since both methods will function the same, you can choose whichever method you like.

How to write a Dictionary to JSON file in S3 Bucket using boto3 and Python

If you want to write a python dictionary to a JSON file in S3 then you can use the code examples below.

There are two code examples doing the same thing below because boto3 provides a client method and a resource method to edit and access AWS S3.

Writing Python Dictionary to an S3 Object using boto3 Client

import boto3
import json
from datetime import date

data_dict = {
    'Name': 'Daikon Retek',
    'Birthdate': date(2000, 4, 7),
    'Subjects': ['Math', 'Science', 'History']
}

# Convert Dictionary to JSON String
data_string = json.dumps(data_dict, indent=2, default=str)


# Upload JSON String to an S3 Object
client = boto3.client('s3')

client.put_object(
    Bucket='radishlogic-bucket', 
    Key='s3_folder/client_data.json',
    Body=data_string
)

How to download files from S3 Bucket using boto3 and Python

If you want to download a file from an AWS S3 Bucket using Python, then you can use the sample codes below.

The codes below use AWS SDK for Python named boto3.

boto3 provides three methods to download a file.

download_file()
download_fileobj() – with multipart upload
get_object()

Then for each method, you can use the client class or the resource class of boto3.

Both of the classes will be used for each of the methods above.

Note: All examples will work with any Python3 environment running in Windows, MacOS or Linux operating systems.

How to upload a file to S3 Bucket using boto3 and Python

There are 3 ways to upload or copy a file from your local computer to an Amazon Web Services (AWS) S3 Bucket using boto3. All of these will be discussed in this post including multipart uploads.

The codes below will work if you are Windows, Mac, and Linux. Will also work if you working in a Lambda function using Python.

Each method will have an example using boto3 S3 client and S3 resource so you can use whatever method you are comfortable with.

upload_file method
upload_fileobj method (supports multipart upload)
put_object method

How to get the ARN of an S3 Bucket

Each resource in AWS has an Amazon Resource Name (ARN). An ARN is a unique identifier of your resource. Its value has no duplicate in other accounts and only exists in your account.

It’s used especially in IAM policies where you set which resources you will allow access to.

You can actually predict the ARN of an S3 Bucket since it has a standard format of arn:aws:s3:::S3_BUCKET_NAME.

But if you are like me who is afraid of making a mistake typing the S3 bucket ARN, I prefer going to the AWS Console, searching for the S3 Bucket ARN, and copy-pasting it.

Follow the instructions below to get the S3 Bucket ARN.

Minimum IAM Permission to create S3 presigned URLs

If you wanted to publicly share a file or an object inside a private S3 bucket you will need to create an S3 presigned URL. This will create a temporary link to the S3 file which you can share and access publicly.

As best practice, we must apply the least privileged permission to the IAM user or IAM role that will create the S3 presigned URL. Which brings us to the question, what is the minimum IAM permission to create an S3 presigned URL?

How to download all files in an S3 Bucket using AWS CLI

There are many ways to download files from an S3 Bucket, but if you are downloading an entire S3 Bucket then I would recommend using AWS CLI and running the command aws s3 sync s3://SOURCE_BUCKET LOCAL_DESTINATION.

In the examples below, I’m going to download the contents of my S3 Bucket named radishlogic-bucket.

My S3 Bucket in the AWS Console — My S3 Bucket in the AWS management console

Example 1: Download S3 Bucket to Current Local Folder

If you want to download the whole S3 Bucket in the same folder that you are in, then you should use the command aws s3 sync s3://SOURCE_BUCKET ..

In our example S3 Bucket above, the AWS CLI will be like this.