pysftp putfo creates an empty file on SFTP server but not streaming the content from StringIO

Question

My code first writes lines to a CSV in io.StringIO():

fileBuffer = io.StringIO()

# write header
header_writer = csv.DictWriter(fileBuffer, fieldnames=columnNames)
header_writer.writeheader()

# write lines
writer = csv.writer(fileBuffer, delimiter=',') 

for line in data:
            line_dec = line.decode('ISO-8859-1') 
            # print([line_dec])
            writer.writerow([line_dec])

The following code also prints all expected rows:

$print(fileBuffer.getvalue())    # -> prints all expected rows

I can also successfully connect to the SFTP Server using pysftp and even in the with pysftp the code successfully returns all expected rows:

with pysftp.Connection(host, username=user, password=pw, cnopts=cnopts) as sftp: 
            print('sucessfully connected to {} via Port 22'.format(host))
            print(fileBuffer.getvalue())    # -> prints all expected rows
            sftp.putfo(fileBuffer, file2BeSavedAs)   # -> no rows put on FTP Server

Here comes the actual problem:
Unfortunately, the code only creates the file without writing the data respectively the body into it. On the other hand, my code does not return any error message.

How can I put a CSV from StringIO to an SFTP server?

Answer 1

You have to seek a read pointer of the buffer back to the beginning, before you try to upload the buffer:

fileBuffer.seek(0)
sftp.putfo(fileBuffer, file2BeSavedAs)

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Though a better approach is to write the CSV directly to the server, without an intermediate buffer. Use Connection.open to obtain a file-like object representing a file on the SFTP server:

with sftp.open(file2BeSavedAs, mode='w', bufsize=32768) as f:
    writer = csv.writer(f, delimiter=',') 
    # ...

For the purpose of the bufsize argument, see:
Writing to a file on SFTP server opened using Paramiko/pysftp "open" method is slow

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For a similar question, with progress display, see:
How to use Paramiko getfo to download file from SFTP server to memory to process it

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Though pysftp is dead. You better use Paramiko. See pysftp vs. Paramiko. With Paramiko the code would be pretty much the same.