I issue this statement: db = cx_Oracle.connect("user/pass@IP/BKTDW")
and I get this error: 
Traceback (most recent call last):
  File "", line 1, in 
cx_Oracle.DatabaseError: Error while trying to retrieve text for error ORA-01804
It seems that connect method doen't work at all. I have installed the Oracle Client and I am connecting normally via Toad or Sql Developer. 
Please Help!
Ensure that sqlplus is working from cmd line. It could be if on 64bit windows in has in PATH there is a target to non-64 bin version of oracle bin folder. In our case we ensured that 64bit location is placed in PATH . For instance place c:\Oracle\Ora11g_r2_x64\bin\  and remove c:\Oracle\ora11g_2\bin\, it was not related with ORACLE_HOME .
Can't connect with cx_Oracle of Python to oracle remote database