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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _pypi_push(dist):
 """Push created package to PyPI. Requires the following defined environment variables: - TWINE_USERNAME: The PyPI username to upload this package under - TWINE_PASSWORD: The password to the user's account Args: dist (str):
 The distribution to push. Must be a valid directory; shell globs are NOT allowed. """

    # Register all distributions and wheels with PyPI. We have to list the dist
    # directory and register each file individually because `twine` doesn't
    # handle globs.
    for filename in os.listdir(dist):
        full_path = os.path.join(dist, filename)
        if os.path.isfile(full_path):
            # This will fail if the project has never been uploaded, so use check=false
            _shell('twine register ' + shlex.quote(full_path), check=False)

    _shell('twine upload ' + shlex.quote(dist + '/*'))