tsql utility (FreeTDS) can connect to SQL Server but pymssql cannot

I met a really weird issue: I'm able to connect to my SQL Server with tsql but I'm not able to do the same with pymssql. Let me give you more details.

With this kind of tsql command everything seems to be ok:

$ tsql -H '10.10.10.2' -U 'DOMAIN\myuser' -p 63849
Password: 
locale is "fr_FR.UTF-8"
locale charset is "UTF-8"
using default charset "UTF-8"
1>

But with the following basic python script I got an issue:

$ cat test_mssql.py
# -*- coding: utf8 -*-
import pymssql
import pandas as pd

conn = pymssql.connect(server=r'10.10.10.2', user=r'DOMAIN\myuser', password='mypassword', port='63849')

$ python test_mssql.py
Traceback (most recent call last):
File "api-vinci-rh/current/test_mssql.py", line 60, in <module>
conn = pymssql.connect(server=r'10.10.10.2', user=r'DOMAIN\myuser', password='mypassword', port='63849')
File "pymssql.pyx", line 641, in pymssql.connect (pymssql.c:10788)
pymssql.OperationalError: (20002, 'DB-Lib error message 20002, severity 9:\nAdaptive Server connection failed\n')

By activating TDSDUMPCONFIG env variable, I can see a difference between the tls command and my python script:

TDSDUMPCONFIG tls trace
config.c:224:Final connection parameters:
config.c:225:            server_name = 10.10.10.2
config.c:226:       server_host_name = 10.10.10.2
config.c:227:                ip_addr = 10.10.10.2
config.c:228:          instance_name = 
config.c:229:                   port = 63849
config.c:230:          major_version = 7
config.c:231:          minor_version = 1
config.c:232:             block_size = 0
config.c:233:               language = us_english
config.c:234:         server_charset = 
config.c:235:        connect_timeout = 0
config.c:236:       client_host_name = myhost
config.c:237:         client_charset = UTF-8
config.c:238:               app_name = TSQL
config.c:239:              user_name = DOMAIN\myuser
config.c:242:                library = TDS-Library
config.c:243:              bulk_copy = 0
config.c:244:      suppress_language = 0
config.c:245:          encrypt level = 0
config.c:246:          query_timeout = 0
config.c:249:               database = 
config.c:250:              dump_file = /tmp/freetds.log
config.c:251:            debug_flags = 0


TDSDUMPCONFIG pymssql trace
config.c:224:Final connection parameters:
config.c:225:            server_name = 10.10.10.2:63849
config.c:226:       server_host_name = 10.10.10.2
config.c:227:                ip_addr = 10.10.10.2
config.c:228:          instance_name = 
config.c:229:                   port = 63849
config.c:230:          major_version = 7
config.c:231:          minor_version = 1
config.c:232:             block_size = 0
config.c:233:               language = us_english
config.c:234:         server_charset = 
config.c:235:        connect_timeout = 0
config.c:236:       client_host_name = myhost
config.c:237:         client_charset = UTF-8
config.c:238:               app_name = pymssql=2.1.2
config.c:239:              user_name = 
config.c:242:                library = DB-Library
config.c:243:              bulk_copy = 0
config.c:244:      suppress_language = 0
config.c:245:          encrypt level = 0
config.c:246:          query_timeout = 0
config.c:249:               database = 
config.c:250:              dump_file = /tmp/freetds.log
config.c:251:            debug_flags = 0
config.c:252:              text_size = 64512
config.c:253:           broken_dates = 0
config.c:254:     emul_little_endian = 0
config.c:255:      server_realm_name = 

I think the 2 main differences is about the user_name which is empty with the python script and the library which is DB-Library instead of TDS-Library.

I currently find no way to force these parameters in the python script and I find no clue about my issue (the error message is a generic one).

I'm using python 2.7.9 and pymssql==2.1.2 More info about my env:

$ tsql -C
Compile-time settings (established with the "configure" script)
                            Version: freetds v0.91
             freetds.conf directory: /etc/freetds
     MS db-lib source compatibility: no
        Sybase binary compatibility: yes
                      Thread safety: yes
                          iconv library: yes
                        TDS version: 4.2
                              iODBC: no
                           unixodbc: yes
              SSPI "trusted" logins: no
                           Kerberos: yes

$ grep -v '^#' /etc/freetds/freetds.conf 
[global]
    tds version = 7.1
    dump file = /tmp/freetds.log
    text size = 64512
    enable gssapi delegation = off

If you have any clue to help let me know.

Edit: I have another SQL Server instance for my test and my python script works... the username in the TDSDUMPCONFIG is set. So Iguess there is something strange on my env but don't know what