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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 bib_path(self):
 """Absolute file path to the .bib bibliography document."""

        bib_name = self.bib_name
        # FIXME need to bake in search paths for tex documents in all platforms
        osx_path = os.path.expanduser(
            "~/Library/texmf/bibtex/bib/{0}".format(bib_name))
        if self._file_exists(bib_name):
            return bib_name  # bib is in project directory
        elif os.path.exists(osx_path):
            return osx_path
        else:
            return None