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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 _url_base64_encode(msg):
 """ Base64 encodes a string using the URL-safe characters specified by Amazon. """

        msg_base64 = base64.b64encode(msg)
        msg_base64 = msg_base64.replace('+', '-')
        msg_base64 = msg_base64.replace('=', '_')
        msg_base64 = msg_base64.replace('/', '~')
        return msg_base64