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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 parse_device_list(device_list_str, key):
 """Parses a byte string representing a list of devices. The string is generated by calling either adb or fastboot. The tokens in each string is tab-separated. Args: device_list_str: Output of adb or fastboot. key: The token that signifies a device in device_list_str. Returns: A list of android device serial numbers. """

    clean_lines = new_str(device_list_str, 'utf-8').strip().split('\n')
    results = []
    for line in clean_lines:
        tokens = line.strip().split('\t')
        if len(tokens) == 2 and tokens[1] == key:
            results.append(tokens[0])
    return results