Running Python script with temporary environment variables

Question

I have a Python application and it utilizes environment variables in Kubernetes configuration such as:

apiVersion: v1
kind: ConfigMap
metadata:
  name: my-config
  namespace: default
data:
  var1: foo
  var2: bar

---

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
  namespace: default
spec:
  containers:
    - envFrom:
      - configMapRef:
          name: my-config

So, it is fine when the app is Dockerized and running on a Kubernetes farm.

However, when running the application on a local machine without Docker and Kubernetes but a humble command:

python app.py

I have to make the Python modules find the environment variables with os.getenv('var1') even if there is no ConfigMap or Pod on.

Is it possible to without a need to add extra code in Python modules or adding environment variables to the local machine system?

Answer 1

you can set the environment variable intended by add the key-value pair in os module's environ dictionary.

import os 

os.environ['intended var'] = 'intended value'

Sample run

>>> os.getenv('intended var')
'intended value'

Answer 2

In a shell, you could also simply temporarily assign the value(s) for the environment variable(s) right before calling the script. No need to change your script at all.

Consider the following app.py which just prints the environment variables ENV_PARAM and ENV_PARAM2:

#!/usr/bin/env python3
import os

print(os.environ['ENV_PARAM'])
print(os.environ['ENV_PARAM2'])

When the vars are not set and you call it like this

python app.py

you will get a KeyError.

KeyError: 'ENV_PARAM'

When you instead specify the values in the same line and call it like this

ENV_PARAM='foo' ENV_PARAM2='bar' python app.py

it works fine. Output:

foo
bar

This will not set the environment variable beyond that, so if you do

echo "$ENV_PARAM"  

afterwards, it will return nothing. The environment variable was only set temporary, like you required.