os.getenv('DP_MY_WORD_VECTOR') return None

Question

I run the python project in terminal of VS code remote anconda environment.I wrote the DP_MY_WORD_VECTOR variable in a .env file, and want to get the value in code.I used the os.getenv() and it worked well when debugging, but didn't work when run the .py file. I'm not sure what cause the problem?