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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 _update_version(self, version):
 """Find out where to change the version and change it. There are three places where the version can be defined. The first one is an explicitly defined Python file with a ``__version__`` attribute. The second one is some version.txt that gets read by setup.py. The third is directly in setup.py. """

        if self.get_python_file_version():
            setup_cfg = pypi.SetupConfig()
            filename = setup_cfg.python_file_with_version()
            lines = open(filename).read().split('\n')
            for index, line in enumerate(lines):
                match = UNDERSCORED_VERSION_PATTERN.search(line)
                if match:
                    lines[index] = "__version__ = '%s'" % version
            contents = '\n'.join(lines)
            open(filename, 'w').write(contents)
            logger.info("Set __version__ in %s to %r", filename, version)
            return

        versionfile = self.filefind(['version.txt', 'version'])
        if versionfile:
            # We have a version.txt file but does it match the setup.py
            # version (if any)?
            setup_version = self.get_setup_py_version()
            if not setup_version or (setup_version ==
                                     self.get_version_txt_version()):
                open(versionfile, 'w').write(version + '\n')
                logger.info("Changed %s to %r", versionfile, version)
                return

        good_version = "version = '%s'" % version
        line_number = 0
        setup_lines = open('setup.py').read().split('\n')
        for line in setup_lines:
            match = VERSION_PATTERN.search(line)
            if match:
                logger.debug("Matching version line found: %r", line)
                if line.startswith(' '):
                    # oh, probably '    version = 1.0,' line.
                    indentation = line.split('version')[0]
                    # Note: no spaces around the '='.
                    good_version = indentation + "version='%s'," % version
                setup_lines[line_number] = good_version
                break
            line_number += 1
        contents = '\n'.join(setup_lines)
        open('setup.py', 'w').write(contents)
        logger.info("Set setup.py's version to %r", version)