Export variables from .env file and get them from os.environ without python-dotenv

I want to use couple env variables in my python script. I created .env file with:

TEST='test'

then create main.py:

import os
print(os.getenv("TEST"))
print(os.environ['TEST'])

execute in same dir:

$ source .env
$ echo $TEST
test

then run:

$ python3 main.py
None
Traceback (most recent call last):
  File "/Users/me/temp/pt/main.py", line 3, in <module>
    print(os.environ['TEST'])
  File "/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/os.py", line 679, in __getitem__
    raise KeyError(key) from None
KeyError: 'TEST'

Why in this case os.getenv is not work and work only after export TEST=test executing or with python-dotenv module using?

TL;DR Don't use source to process dotenv files; they are not shell scripts.

The immediate problem is that source does not export any of the variables defined by the file; you are only defining regular shell variables that do not appear in the environment of the new Python process.

You can work around that by enabling the -a option to auto-export any variables defined in the file.

$ set -a
$ source .env
$ python3 main.py
test
test

However, the bigger problem here is that .env files are not shell scripts. The quoting rules followed by dotenv are different. Compare:

$ cat .env
TEST=test echo hello
$ cat main.py
import os
import dotenv
x = dotenv.dotenv_values('.env')
print(os.getenv("TEST"))
print(x['TEST'])
$ set -a
$ source .env
hello
$ python3 main.py
None
test echo hello

Sourcing the file does not define a variable TEST; instead, it executes the echo command that ignores the value of TEST set only for its environment.

Processing the file with dotenv produces a variable named TEST set to the full string test echo hello.

Try these steps:

1. pip install python-dotenv
2. Import the package in your python script:
   • from dotenv import load_dotenv
   • import os
3. Load the environment variables from the .env file:
   • load_dotenv()
4. my_var = os.getenv('TEST')