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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 v_unique_name_leaf_list(ctx, stmt):
 """Make sure config true leaf-lists do nothave duplicate defaults"""


    if not stmt.i_config:
        return
    seen = []
    for defval in stmt.i_default:
        if defval in seen:
            err_add(ctx.errors, stmt.pos, 'DUPLICATE_DEFAULT', (defval))
        else:
            seen.append(defval)