Why prefix can't be passed to Env.__init__?

[paduszyk]

The package supports prefixing the variable names, as added in #363. However, the default value is hardcoded to an empty string in the initializer. IMHO, a much more natural way for defining prefixes would be:

env = environ.Env(prefix="DJANGO_")

instead of the current:

env = environ.Env()
env.prefix = "DJANGO_"

In the case of the proposed solution, IDEs would hint to the user that they can define prefixes for their vars.

Of course, passing prefix as a keyword argument will break **scheme. However, the "kwargs" related to the scheme, could be detected by checking the uppercase keys of the scheme dict. But that's the issue for another ticket, I guess.