Hans-Peter>  Well, yesterday, I tried to parse some simple hexdump,
    Hans-Peter>  produced by tcpdump -xs1500 port 80. The idea was, filter
    Hans-Peter>  the hexcodes, and display and 7 bit acsii codes like a
    Hans-Peter>  little advanced hex monitors do.

    Hans-Peter>  As I'm fairly new to advanced regex constructs, would
    Hans-Peter>  somebody enlight me, how to efficiently parse lines like:

    Hans-Peter>     2067 726f 7570 732e 2e2e 3c2f 613e 3c2f
    Hans-Peter>     666f 6e74 3e3c 2f74 643e 3c2f 7472 3e3c
    Hans-Peter>     7472 3e3c 7464 2062 6763 6f6c 6f72 3d23
    Hans-Peter>     6666 6363 3333 2063 6f6c 7370 616e 3d34
    Hans-Peter>     3e3c 494d 4720 6865 6967 6874 3d31 2073
    Hans-Peter>     7263 3d22 2f69 6d61 6765 732f 636c 6561
    Hans-Peter>     7264 6f74 2e67 6966 2220 7769 6474 683d
    Hans-Peter>     3120 3e3c 2f74 643e 3c2f 7472 3e3c 2f74
    Hans-Peter>     6162 6c65 3e3c 703e 3c66 6f6e 7420 7369
    Hans-Peter>     7a65 3d2d 313e 4172 6520 796f 7520 6120

    Hans-Peter>  with respect to varying column numbers. I will refrain to
    Hans-Peter>  show my stupid beginnings, but I wasn't able to get that
    Hans-Peter>  _one_ regex right, with all columns in matchobj.groups()
    Hans-Peter>  listed.

I'm not sure quite what you're looking for, but this data is so regular I
wouldn't use regular expressions to parse it (no pun intended).

Assuming the above stream is coming in on stdin and I wanted to display
any printable ASCII characters, I'd start with something like this:

    import sys

    for line in sys.stdin.readlines():
        line = line.strip()
        fields = line.split()
        printing = []
        for pair in fields:
            first = chr(int(pair[:2], 16))
            second = chr(int(pair[2:], 16))
            if first < " " or first >  "~":
                first = "."
            if second < " " or second >  "~":
                second = "."
            printing.extend([first, second])
        print line, "".join(printing)

The above hex data fed to this code produces

    2067 726f 7570 732e 2e2e 3c2f 613e 3c2f  groups...</a> </
    666f 6e74 3e3c 2f74 643e 3c2f 7472 3e3c font> </td></tr><
    7472 3e3c 7464 2062 6763 6f6c 6f72 3d23 tr> <td bgcolor=#
    6666 6363 3333 2063 6f6c 7370 616e 3d34 ffcc33 colspan=4
    3e3c 494d 4720 6865 6967 6874 3d31 2073 > <IMG height=1 s
    7263 3d22 2f69 6d61 6765 732f 636c 6561 rc="/images/clea
    7264 6f74 2e67 6966 2220 7769 6474 683d rdot.gif" width=
    3120 3e3c 2f74 643e 3c2f 7472 3e3c 2f74 1 > </td></tr></t
    6162 6c65 3e3c 703e 3c66 6f6e 7420 7369 able> <p><font si
    7a65 3d2d 313e 4172 6520 796f 7520 6120 ze=-1> Are you a 

on stdout.

-- 
Skip Montanaro (skip@pobox.com)
http://www.mojam.com/
http://www.musi-cal.com/

-- 
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