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pythoniopcappacket-sniffers

Python writing to file same amount of bytes

I was trying to write Pcap generator and I want to write fixed length of bytes to file. Frame length that I sniff is always changeable obviously but I should also define this length in Pcap packet header. I set it as 1500 bytes. Is there any way to put leading zeros to byte object that complete it to 1500 bytes?

Solution

  • Use bytes.zfill.

    >>> bs = bytes([1, 2, 3])
>>> bs
b'\x01\x02\x03'
>>> padded = bs.zfill(10)
>>> padded
b'0000000\x01\x02\x03'

    This is the documentation for bytes.zfill:

    bytes.zfill(width)

    bytearray.zfill(width)

    Return a copy of the sequence left filled with ASCII b'0' digits to make a sequence of length width. A leading sign prefix (b'+'/ b'-' is handled by inserting the padding after the sign character rather than before. For bytes objects, the original sequence is returned if width is less than or equal to len(seq).