def required_versions(vers):
    """
    Create python_requires stirng of supported python versions.

    >>> required_versions([2.7, 3.3, 3.4])
    ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*"

    :param list vers: List of python versions as floats.
    :returns: A string of supported python versions
    :rtype: str
    """
    vers.sort()
    if 2.7 in vers:
        requires = [">=2.7"]
        py3vers = [ver for ver in vers if ver >= 3]
        if py3vers:
            low_ver = py3vers[0]

            start = 3.0
            while start < low_ver:
                requires.append("!={}.*".format(round(start, 1)))
                start += 0.1

        return ", ".join(requires)
    else:
        return ">={}".format(vers[0])