Read a CSV file from S3 without saving it to the disk

# src.py
import boto3
import tempfile
import csv
import io

BUCKET_NAME = "foo-bucket"
OBJECT_NAME = "foo-file.csv"

s3 = boto3.client("s3")

# 'w+b' allows both reading from and writing to the file.
with tempfile.NamedTemporaryFile("w+b") as f:
    s3.download_fileobj(BUCKET_NAME, OBJECT_NAME, f)

    # This sets the file handle back to the beginning of the file.
    # Without this, the loaded file will show no content.
    f.seek(0)

    # Here, 'io.TextIOWrapper' is converting the binary content of
    # the file to be compatible with text content.
    csv_reader = csv.DictReader(
        io.TextIOWrapper(f, encoding="utf-8"),
    )

    # Now you're good to go.
    for row in csv_reader:
        # ... do processing
        ...