The API call to retrieve a user by email address is actually not protected behind admin login. It is only privileged if the ACP setting to hide user email addresses is enabled:
You should be able to use an API v3 token (generated from Settings > API Access) to make this call as an administrative user, if you are not willing to change the aforementioned option.
I am not familiar with Python, but the equivalent cURL command using an API v3 token would be:
curl -H "Authorization: Bearer your_bearer_token" localhost:4567/api/user/email/[email protected]