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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 main():
 """Writes out newsfile if significant version bump"""

    last_known = '0'
    if os.path.isfile(metafile):
        with open(metafile) as fh:
            last_known = fh.read()

    import mbed_cloud
    current = mbed_cloud.__version__

    # how significant a change in version scheme should trigger a new changelog entry
    # (api major, api minor, sdk major, sdk minor, sdk patch)
    sigfigs = 4
    current_version = LooseVersion(current).version
    last_known_version = LooseVersion(last_known).version

    should_towncrier = current_version[:sigfigs] != last_known_version[:sigfigs]

    print('%s -- %s :: current vs previous changelog build' % (current, last_known))
    if should_towncrier:
        print('%s >> %s :: running changelog build' % (current, last_known))
        subprocess.check_call(
            ['towncrier', '--yes'],
            cwd=os.path.join(PROJECT_ROOT, 'docs', 'changelog')
        )
        with open(metafile, 'w') as fh:
            fh.write(current)