An environment variable reader.

Raised when validation fails against one or all of the parsed environment variables.

Raised when an environment variable or if a required environment variable is unset.

Raised when trying to parse new values after an `Env` has already been sealed.

An environment variable reader that supports reading values from files.

Raised when adding a custom parser that conflicts with a built-in parser method.

Same as marshmallow.fields.TimeDelta with extra duration string support. Supports ordered duration strings (loosely based on GEP-2257), e.g.

Same as `marshmallow.fields.Url` but deserializes to a `urllib.parse.ParseResult`.