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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 _safe_name(file_name, sep):
 """Convert the file name to ASCII and normalize the string."""

    file_name = stringify(file_name)
    if file_name is None:
        return
    file_name = ascii_text(file_name)
    file_name = category_replace(file_name, UNICODE_CATEGORIES)
    file_name = collapse_spaces(file_name)
    if file_name is None or not len(file_name):
        return
    return file_name.replace(WS, sep)