Append to existing file on SFTP server via pysftp

Question

I have one file named Account.txt in SFTP server, and I'm trying to appending a line to this file. This is my effort:

from io import StringIO
from pysftp import Connection, CnOpts

cnopts = CnOpts()
cnopts.hostkeys = None
with Connection('ftpserver.com'
                ,username= 'username'
                ,password = 'password'
                ,cnopts=cnopts
                ) as sftp:
    with sftp.cd('MY_FOLDER'):
        f = sftp.open('Account.txt', 'ab')
        data='google|33333|Phu|Wood||true|2018-09-21|2018-09-21|google'
        f.write(data+'\n')

When I run this above code, the file was overwritten, instead of appended. So, How can append new line but still keep the old lines in the file?

For example:

Account.txt file:

facebook|11111|Jack|Will||true|2018-09-21|2018-09-21|facebook
facebook|22222|Jack|Will||true|2018-09-21|2018-09-21|facebook

And now I want to add line "google|33333|Phu|Wood||true|2018-09-21|2018-09-21|google" to the file. The result I'm expecting:

Account.txt file

facebook|11111|Jack|Will||true|2018-09-21|2018-09-21|facebook
facebook|22222|Jack|Will||true|2018-09-21|2018-09-21|facebook
google|33333|Phu|Wood||true|2018-09-21|2018-09-21|google

Hope you guys can understand. Leave a comment if you don't. Thank you.

Your code works for me. - *"new line appended to the file, but all the old lines have been deleted"* This is not really clear to me. Do you mean that the file was actually overwritten, instead of appended to? + What is your SFTP server? — Martin Prikryl, Nov 29 '18 at 08:44
Yes, You are right. The file was overwritten, instead of appended. Sorry, I'm not really good at English. @MartinPrikryl — Han Van Pham, Nov 29 '18 at 08:50
Did you mean the hostname? I'm sorry I can not share it for you now. — Han Van Pham, Nov 29 '18 at 08:56
Did you test your code against some more common SFTP server, like OpenSSH? As it works for me with OpenSSH just fine. So it can be server-side bug. — Martin Prikryl, Nov 29 '18 at 09:07
Thanks, bro. Hmmm, the situation is I can not fix the SFTP server now. May we have another way, bro? — Han Van Pham, Nov 29 '18 at 09:11

score 1 · Accepted Answer · edited Nov 18 '20 at 11:57

1

Your code works for me with OpenSSH SFTP server.

Maybe it's a bug in Core FTP server.

You can instead try manually seeking file write pointer to the end of the file:

with sftp.open('Account.txt', 'r+b') as f:
    f.seek(0, os.SEEK_END)
    data='google|33333|Phu|Wood||true|2018-09-21|2018-09-21|google'
    f.write(data+'\n')

edited Nov 18 '20 at 11:57

Basj

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answered Nov 29 '18 at 09:13

Martin Prikryl

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score -1 · Answer 2 · answered Nov 18 '20 at 11:56

-1

An addition to Martin's answer:

When using r+b, it will fail if the file does not exist yet. Use a+ instead if you want the file to be created if it does not exist, in a similar way to Difference between modes a, a+, w, w+, and r+ in built-in open function?.

Then no f.seek(0, os.SEEK_END) will be needed:

with sftp.open('test.txt', 'a+') as f:
    f.write('hello')

answered Nov 18 '20 at 11:56

Basj

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The OP knows that the right way is to use the `a` mode. The point of this question is that the `a` mode does not work on that particular server. – Martin Prikryl Nov 18 '20 at 12:21
Indeed, the `b` is wrong. But it's ignored by Paramiko. Only `a` remains. – Martin Prikryl Nov 20 '20 at 09:25

Append to existing file on SFTP server via pysftp

2 Answers2