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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 version_str(version):
 """Convert a version tuple or string to a string. Should be returned in the form: major.minor.release """

    if isinstance(version, str):
        return version
    elif isinstance(version, tuple):
        return '.'.join([str(int(x)) for x in version])
    else:
        raise ValueError("Invalid version: %s" % version)