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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 patches_base_ref(default=exception.CantGuess):
 """Return a git reference to patches branch base. Returns first part of .spec's patches_base is found, otherwise return Version(+%{milestone}). """

    ref = None
    try:
        spec = specfile.Spec()
        ref, _ = spec.get_patches_base(expand_macros=True)
        if ref:
            ref, _ = tag2version(ref)
        else:
            ref = spec.get_tag('Version', expand_macros=True)
            milestone = spec.get_milestone()
            if milestone:
                ref += milestone
        if not ref:
            raise exception.CantGuess(msg="got empty .spec Version")
    except Exception as ex:
        if default is exception.CantGuess:
            raise exception.CantGuess(
                what="current package version",
                why=str(ex))
        else:
            return default
    tag_style = version_tag_style(ref)
    return version2tag(ref, tag_style=tag_style)