Packing and unpacking IP addresses into 32-bit integers
Steven D. Majewski
sdm7g at Virginia.EDU
Mon Aug 9 22:50:29 CEST 1999
On 9 Aug 1999, Ben Gertzfield wrote:
> I noticed that the 'socket' module in Python has slightly different
> behavior for gethostbyname() than I'm used to.
> In Python, gethostbyname() returns a string, not a packed IP address
> (a 32-bit integer) of the IP address, as C and Perl do. However, I
> need to talk with C over the network, and the 'struct' module doesn't
> deal with packing or unpacking IP addresses.
> Do I have to use a regular expression to split up the dotted quads
> that gethostbyname() returns into the component bytes and then use
> binary shifts and or'ing to get them into a standard 32-bit integer
> format? Or is there a better way that I'm totally missing?
No you don't have to use regular expressions and binary shifts and or's:
First, map int or string.atoi onto the result of applying string.split
to the return string of gethostbyname -- that will give you a list of ints.
adr = map( string.atoi, string.split( gethostbyname( name ), '.' ))
and use either struct.pack or array to coerce it into a binary string:
a = apply( struct.pack, [ 'bbbb' ] + adr )
(or longer, but less cryptically)
a = array( 'b')
a.fromlist( adr )
---| Steven D. Majewski (804-982-0831) <sdm7g at Virginia.EDU> |---
---| Department of Molecular Physiology and Biological Physics |---
---| University of Virginia Health Sciences Center |---
---| P.O. Box 10011 Charlottesville, VA 22906-0011 |---
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