monkey patch s3 streamingbody to be streamable for csv for example

s3-streaming-fileobj.py

import boto3
import io
import csv
from functools import partial

s3c = boto3.client('s3')

def logging_read(read, amt):
    print('READ {}'.format(amt))
    return read(amt)

def csv_from_object(bucket, key):
    body = s3c.get_object(Bucket=bucket, Key=key)['Body']

    # uncomment to see reads
    # setattr(body, 'read', partial(logging_read, body.read))

    # these "implement" the io.IOBase interface
    setattr(body, 'readable', lambda: True)
    setattr(body, 'writable', lambda: False)
    setattr(body, 'seekable', lambda: False)
    setattr(body, 'closed', False)
    setattr(body, 'flush', lambda: 'noop')
    with io.TextIOWrapper(body, newline='') as buf_wrapper:
        # we have to yield from instead of return to keep TextIOWrapper alive
        yield from csv.DictReader(buf_wrapper)

for row in csv_from_object('bucket', 'something.csv'):
    print(row)