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Full Discussion: Python, struct.pack
Top Forums Programming Python, struct.pack Post 302471541 by Dedalus on Saturday 13th of November 2010 01:32:07 PM
Old 11-13-2010
Python, struct.pack

Hello,

I found some code on line.
Is a python function that bring up an Internet interface, here the code:
Code:
        # Get existing device flags
        ifreq = struct.pack('16sh', 'wlan0', 0)
        flags = struct.unpack('16sh', fcntl.ioctl(sockfd, SIOCGIFFLAGS, ifreq))[1]

I'm starting reading something about it. I know that the struct.pack is needed for compatibility with C struct.
But why we pack the wlan0 exactly with 16 string and 1 short (and not 30s10h)?
In my case for example I get:
Quote:
ifreq = wlan0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00
and
Quote:
fcntl.ioctl(sockfd, SIOCGIFFLAGS, ifreq) give me:
wlan0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00C\x10
the final result unpacking everything is 4163.
Is it because from the fcntl.ioctl (in this case) I will expect to fill it with string and short?

Thanks

D
 

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PYCENTRAL()															       PYCENTRAL()

NAME
pycentral - register and build utility for Python packages SYNOPSIS
pycentral [-h] [-v] <cmd> [<cmd options>] [<args>] DESCRIPTION
pycentral provides support for installing python modules independent of the current installed Python version and handling byte-compilation and -removal tasks in installation scripts. OPTIONS
-v, --version Limit the output to the version numbers of the python versions. -h, --help Print a help text. pycentral has the following sub commands. For fine grained help, call: pycentral <cmd>. bccompile Byte compile .py files in a package. bcremove Remove the byte compiled .py files. list List all managed files. pkginstall Make a package available for all supported runtimes. pkgprepare Prepare a package for all supported runtimes. pkgremove Remove a package installed for all supported runtimes. pkglist List pycentral-managed files of a package for all supported runtimes. rtinstall Make installed packages available for this runtime. rtremove Remove packages installed for this runtime. updatedefault Update the default python version. debhelper move files to pycentral locaation, variable substitutions (called by dh_pycentral). pycentraldir <package> Show the installation directory used by pycentral for <package>. showdefault Show default python version number. Deprecated, use pyversions(1) showsupported Show the supported python versions. Deprecated, use pyversions(1) showversions Show version numbers of supported python versions. Deprecated, use pyversions(1) dh_pycentral, should not be called directly). version Show the pycentral version. FILES
/etc/python/debian_config is searched for the attribute overwrite-local. If set to 1, or True, existing files in /usr/lib/pythonX.Y/*-packages are overwritten with symbolic links to the pycentral install area. The default is to abort the installation of a package, when files already exist. This behaviour may be useful, when python libraries were manually installed into this directory. The attribute byte-compile can be set to a comma separated list of the values standard and optimze to indicate how files should be byte- compiled. SEE ALSO
pyversions(1), Python policy. AUTHOR
Matthias Klose PYCENTRAL()
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