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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 fix_hashbang(self, contents, python):
 """ Rewrite hashbangs_ to use the correct Python executable. :param contents: The contents of the script whose hashbang should be fixed (a string). :param python: The absolute pathname of the Python executable (a string). :returns: The modified contents of the script (a string). .. _hashbangs: http://en.wikipedia.org/wiki/Shebang_(Unix) """

        lines = contents.splitlines()
        if lines:
            hashbang = lines[0]
            # Get the base name of the command in the hashbang.
            executable = os.path.basename(hashbang)
            # Deal with hashbangs like `#!/usr/bin/env python'.
            executable = re.sub(b'^env ', b'', executable)
            # Only rewrite hashbangs that actually involve Python.
            if re.match(b'^python(\\d+(\\.\\d+)*)?$', executable):
                lines[0] = b'#!' + python.encode('ascii')
                logger.debug("Rewriting hashbang %r to %r!", hashbang, lines[0])
                contents = b'\n'.join(lines)
        return contents