The readme briefly mentions read_env(), however it wasn't until reading the source that the following became apparent:

• that the values read in from the .env file are overridden by any that already existed in the environment (I think this is handy, but isn't immediately obvious)
• that read_env() also takes an overrides list
• that read_env() updates os.environ directly, rather than just that particular Env instance (someone not realising this was intentional is what caused Why read_env reads everything to os.environ? #66 to be filed)

It would be great to mention the above in the readme. If I get a chance to open a PR I will, but it may not be soon, so if anyone wants to do so in the meantime, go ahead :-)