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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 get_current_container_id(read_from='/proc/self/cgroup'):
 """ Get the ID of the container the application is currently running in, otherwise return `None` if not running in a container. This is a best-effort guess, based on cgroups. :param read_from: the cgroups file to read from (default: `/proc/self/cgroup`) """


    if not os.path.exists(read_from):
        return

    with open(read_from, 'r') as cgroup:
        for line in cgroup:
            if re.match('.*/[0-9a-f]{64}$', line.strip()):
                return re.sub('.*/([0-9a-f]{64})$', '\\1', line.strip())