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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 ask_captcha(length=4):
 """Prompts the user for a random string."""

    captcha = "".join(random.choice(string.ascii_lowercase) for _ in range(length))
    ask_str('Enter the following letters, "%s"' % (captcha), vld=[captcha, captcha.upper()], blk=False)