Hello, You should not use Type 66 for calling Python - it is specific to the EES program. There are two types in the Trnsys 18 standard version to call Python: Utility\Calling External Programs\Python\Direct Call Utility\Calling External Programs\Python\Using IO File They are documented in the manual. You may also want to try coupling with Python via sockes or via CFF. Both types are made available for free here: https://gitlab.com/trnstore/trnstore/-/tree/main/Utility/Calling%20External%20Programs The advantage of these types vs the standard types is that you can use customized Python environments (importing any third-party modules such as numpy etc.). Werner >Mr/Ms, >When I tried to simulate TRNSYS with Python, the error occurred that “unable to start a required program with the callprogramm utilly. This may be a problem with Type66 or Type56/TRNBuild. Reported information: file not found error.’ I wonder how I can handle it. If you can do me a favor, I will appreciate it. The screenshot of the errors is attached. > >Best regards, >XIAO Ziwei |