Indicate a directory on Amazon’s S3

I’m new to AWS services. I’ve always used the code below to calculate NDVI for images that were located in a directory.

path = r'images'
dirContents = os.listdir(path)

for file in dirContents:
    if os.path.isdir(file):
        subDir = os.listdir(file)
        
        # Assuming only two files in each subdirectory, bands 4 and 8 here
        if "B04" in subDir[0]:
            band4 = rasterio.open(subDir[0])
            band8 = rasterio.open(subDir[1])
        else:
            band4 = rasterio.open(subDir[1])
            band8 = rasterio.open(subDir[0])

        red = band4.read(1).astype('float32')
        nir = band8.read(1).astype('float32')

        #compute the ndvi
        ndvi = (NIR.astype(float) - RED.astype(float)) / (NIR+RED)

        profile = red.meta
        profile.update(driver='GTiff')
        profile.update(dtype=rasterio.float32)

        with rasterio.open(outfile, 'w', **profile) as dst:
            dst.write(ndvi.astype(rasterio.float32))

Now all the necessary images are in an amazon S3 folder. How do I replace the lines below?

path = r'images'
dirContents = os.listdir(path)

Answer

Amazon S3 is not a filesystem. You will need to use different commands to:

• List the contents of a bucket/path
• Download the files to local storage
• Then access the files on local storage

You can use the boto3 AWS SDK for Python to access objects stored in S3.

For example:

import boto3

s3_resource = boto3.resource('s3')

# List objects
objects = s3_resource.Bucket('your-bucket').objects.filter(Prefix='images/')

# Loop through each object
for object in objects:
  s3_resource.Object(object.bucket_name, object.key).download_file('local_filename')
  # Do something with the file here