title: Set or modify an AWS Lambda environment variable with Python boto3
body: <p>i want to set or modify an environment variable in my lambda script.
  I need to save a value for the next call of my script.
  For exemple i create an environment variable with the aws lambda console and don't set value. After that i try this :</p>
  
  <pre><code>import boto3
  import os
  
  if os.environ['ENV_VAR']:
     print(os.environ['ENV_VAR'])
  os.environ['ENV_VAR'] = "new value"
  </code></pre>
  
  <p>In this case my value will never print.
  I tried with :</p>
  
  <pre><code>os.putenv()
  </code></pre>
  
  <p>but it's the same result.
  Do you know why this environment variable is not set ?</p>
  
  <p>Thank you !</p>