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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 _resolve_subkeys(key, separator="."):
 """Resolve a potentially nested key. If the key contains the ``separator`` (e.g. ``.``) then the key will be split on the first instance of the subkey:: ('a', 'b.c') ('d', 'e|f') If not, the subkey will be :data:`None`:: ('foo', None) Args: key (str):
 A string that may or may not contain the separator. separator (str):
 The namespace separator. Defaults to `.`. Returns: Tuple[str, str]: The key and subkey(s). """

    parts = key.split(separator, 1)

    if len(parts) > 1:
        return parts
    else:
        return parts[0], None