Python and IBM DB2: UnicodeDecodeError

I'm getting this error message

UnicodeDecodeError: 'ascii' codec can't decode byte 0xc8 in position 38: ordinal not in range(128)

when I try to execute any sql query in Python, like this one:

>>> import ibm_db
>>> conn = ibm_db.connect("sample","root","root")
>>> ibm_db.exec_immediate(conn, "select * from act")

I checked default encoding and it seems to be 'utf8':

>>> import sys
>>> sys.getdefaultencoding()
'utf-8'

I also know about this thread, where people are discussing quite a similar problem. One of the advices is:

Have you applied the required database PTFs (SI57014 and SI57015 for 7.1 and SI57146 and SI57147 for 7.2)? They are included as a distreq, so they should have been in the order with your PTFs, but won't be automatically applied.

However, I do not know what is database PTF and how to apply it. Need help.

PS. I'm using Windows 10.

EDIT

This is how I get my error message:

>>> print(ibm_db.stmt_errormsg())
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc8 in position 38:    
ordinal not in range(128)

But when I run the same query "select * from act" in DB2 CLP, then it's ok. And this is driver information, whcih I got running this code in Python:

if client:
    print("DRIVER_NAME: string(%d) \"%s\"" % (len(client.DRIVER_NAME), client.DRIVER_NAME))
    print("DRIVER_VER: string(%d) \"%s\"" % (len(client.DRIVER_VER), client.DRIVER_VER))
    print("DATA_SOURCE_NAME: string(%d) \"%s\"" % (len(client.DATA_SOURCE_NAME), client.DATA_SOURCE_NAME))
    print("DRIVER_ODBC_VER: string(%d) \"%s\"" % (len(client.DRIVER_ODBC_VER), client.DRIVER_ODBC_VER))
    print("ODBC_VER: string(%d) \"%s\"" % (len(client.ODBC_VER), client.ODBC_VER))
    print("ODBC_SQL_CONFORMANCE: string(%d) \"%s\"" % (len(client.ODBC_SQL_CONFORMANCE), client.ODBC_SQL_CONFORMANCE))
    print("APPL_CODEPAGE: int(%s)" % client.APPL_CODEPAGE)
    print("CONN_CODEPAGE: int(%s)" % client.CONN_CODEPAGE)
    ibm_db.close(conn)
else:
    print("Error.")

it prints:

DRIVER_NAME: string(10) "DB2CLI.DLL"
DRIVER_VER: string(10) "10.05.0007"
DATA_SOURCE_NAME: string(6) "SAMPLE"
DRIVER_ODBC_VER: string(5) "03.51"
ODBC_VER: string(10) "03.01.0000"
ODBC_SQL_CONFORMANCE: string(8) "EXTENDED"
APPL_CODEPAGE: int(1251)
CONN_CODEPAGE: int(1208)
True

EDIT

I also tried this:

>>> cnx = ibm_db.connect("sample","root","root")
>>> query = "select * from act"
>>> query.encode('ascii')
b'select * from act'
>>> ibm_db.exec_immediate(cnx, query)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
Exception
>>> print(ibm_db.stmt_errormsg())
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc8 in position 38: 
ordinal not in range(128)

As you can see, in this case I also get the very same error message.

SUMMARY

Below are all my attemts:

C:\Windows\system32>chcp
Active code page: 65001

C:\Windows\system32>python
Python 3.4.4 (v3.4.4:737efcadf5a6, Dec 20 2015, 20:20:57) [MSC v.1600 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import ibm_db
>>> cnx = ibm_db.connect("sample","root","root")
>>> ibm_db.exec_immediate(cnx, "select * from act")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Exception
>>> print(ibm_db.stmt_errormsg())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc8 in position 38: ordinal not in range(128)
>>> ibm_db.exec_immediate(cnx, b"select * from act")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Exception: statement must be a string or unicode
>>> query = "select * from act"
>>> query = query.encode()
>>> ibm_db.exec_immediate(cnx, query)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Exception: statement must be a string or unicode
>>> ibm_db.exec_immediate(cnx, "select * from act").decode('cp-1251')
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
Exception