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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_link(pkg_filename):
 """ Given the filename, including md5 fragment, construct the dependency link for PyPI. """

    root = 'https://files.pythonhosted.org/packages/source'
    name, sep, rest = pkg_filename.partition('-')
    parts = root, name[0], name, pkg_filename
    return '/'.join(parts)