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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 sanitize_label(text):
 """Remove characters not accepted in labels key This replaces any non-word characters (alphanumeric or underscore), with an underscore. It also ensures that the first character is a letter by prepending with 'key' if necessary, and trims the text to 100 characters. """

    if not text:
        return text
    text = re.sub('\\W+', '_', text)
    if text[0] in string.digits:
        text = "key_" + text
    elif text[0] == '_':
        text = "key" + text
    return text[:100]