FileMaker Pro uses the somewhat unusual text encoding of Mac OS Roman, hence you should set the encoding as follows:

cnxn = pyodbc.connect(my_dsn)
cnxn.setencoding(encoding='utf-8')
cnxn.setdecoding(pyodbc.SQL_CHAR, encoding='macroman')

It appears the ODBC drivers for FileMaker Pro are somewhat buggy. See the following issues for more info:

• https://github.com/mkleehammer/pyodbc/issues/1456