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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_commits_since(check_name, target_tag=None):
 """ Get the list of commits from `target_tag` to `HEAD` for the given check """

    root = get_root()
    target_path = os.path.join(root, check_name)
    command = 'git log --pretty=%s {}{}'.format('' if target_tag is None else '{}... '.format(target_tag), target_path)

    with chdir(root):
        return run_command(command, capture=True).stdout.splitlines()