I can do this easily using the smart_open package:
from smart_open import open
for line in open('s3://mybucket/myfolder/myfile.csv'):
print(line)
How to do the same using boto3?
P.S. I need to do this in a Python Shell Job in AWS Glue, without having to package smart_open and set it up as a "Python library path" in the Glue Job.