Make twine get password from an env variable

[jankatins]

I used twine with AppVoyer/travis and had to call it with --password %PYPI_PASS%, but this leaks the Password to the log :-(

I found a way not to leak it (calling it as @twine ... in batch files and set+x; twine ...; set -x in bash scripts), but it would be much easier if twine could get the things from environment variables...

[johnnoone]

It would be a nice improvement for any CI. For example it would let create specialized docker containers for building / publishing or let define masked variables into .travis.yml.

It is easy to implement this directly into argparse. here is a snippet that will fetch a value from --my-param cli parameter or a MY_PARAM environment variable:

import argparse


class EnvDefault(argparse.Action):
    """Get default from environment variable
    """

    def __init__(self, env, required=True, default=None, **kwargs):
        default = os.environ.get(env, default)
        self.env = env
        if default:
            required = False
        super().__init__(default=default, required=required, **kwargs)

    def __call__(self, parser, namespace, values, option_string=None):
        setattr(namespace, self.dest, values)


parser = argparse.ArgumentParser()
parser.add_argument('--my-param', action=EnvDefault, env='MY_PARAM',
                    help=('can also be specified using %(env)s '
                          'environment variable'))

[jankatins]

@johnnoone you should add this to the argparse directly, this is great!

I'll will to to make a PR for this and #143 ...