25👍
Okay, disregard my earlier answer, I found the actual problem.
According to the boto3 documentation for the upload_fileobj function, the first parameter (Fileobj) needs to implement a read() method that returns bytes:
Fileobj (a file-like object) — A file-like object to upload. At a minimum, it must implement the read method, and must return bytes.
The read() function on a _io.StringIO object returns a string, not bytes. I would suggest swapping the StringIO object for a BytesIO object, adding in the necessary encoding and decoding.
Here is a minimal working example. It’s not the most efficient solution – the basic idea is to copy the contents over to a second BytesIO object.
import io
import boto3
import csv
buff = io.StringIO()
writer = csv.writer(buff, dialect='excel', delimiter=',')
writer.writerow(["a", "b", "c"])
buff2 = io.BytesIO(buff.getvalue().encode())
bucket = 'changeme'
key = 'blah.csv'
client = boto3.client('s3')
client.upload_fileobj(buff2, bucket, key)
5👍
As explained here using the method put_object rather than upload_fileobj would just do the job right with io.STRINGIO object buffer.
So here, to match the initial example:
client = boto3.client('s3')
client.upload_fileobj(buff2, bucket, key)
would become
client = boto3.client('s3')
client.put_object(Body=buff2, Bucket=bucket, Key=key, ContentType='application/vnd.ms-excel')
1👍
Have you tried calling buff.flush() first? It’s possible that your entirely-sensible debugging check (calling getvalue()) is creating the illusion that the buff has been written to, but isn’t if you don’t call it.