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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 modutf7_encode(data: str) -> bytes: """Encode the string using modified UTF-7. Args: data: The input string to encode. """

    ret = bytearray()
    is_usascii = True
    encode_start = None
    for i, symbol in enumerate(data):
        charpoint = ord(symbol)
        if is_usascii:
            if charpoint == 0x26:
                ret.extend(b'&-')
            elif 0x20 <= charpoint <= 0x7e:
                ret.append(charpoint)
            else:
                encode_start = i
                is_usascii = False
        else:
            if 0x20 <= charpoint <= 0x7e:
                to_encode = data[encode_start:i]
                encoded = _modified_b64encode(to_encode)
                ret.append(0x26)
                ret.extend(encoded)
                ret.extend((0x2d, charpoint))
                is_usascii = True
    if not is_usascii:
        to_encode = data[encode_start:]
        encoded = _modified_b64encode(to_encode)
        ret.append(0x26)
        ret.extend(encoded)
        ret.append(0x2d)
    return bytes(ret)