Evan Jones wrote: > Hello all, > > I'm trying to use sockets to implement a pre-defined network protocol > that requires that I send messages of exactly a certain number of bytes. > In Python, integer values are represented as 4 bytes each (AFAIK.) > However I don't want to always send 4 bytes: sometimes I want to send > one byte, or 11 bytes, or 33 bytes, or any other permutation that's not > a multiple of 4. It seems to make the most sense to use one-byte data > members and concatenate them before sending. > > This is reasonably easy in C (thanks to the uint8_t data type), but with > Python I'm not sure how I'd implement it. The send() method in the > socket module will take any kind of data, but you can't specify the > number of bytes you want to send, so there's no guarantee as to how many > you're actually sending (particularly if you're sending a value that's > regarded in Python as a long integer - who knows how that data is > actually represented in memory behind the scenes!) > > Perhaps since I'm trying to perform low-level operations, Python is > simply the wrong tool for this job. However, I'd very much like to write > this implementation in Python for sake of quick implementation and testing. > In Python 2 you'd use an 8-bit string - though as you surmise you need access to the conversions to and from the primitive data types. This is provided by the struct module.
In Python 3 you'll use a bytes object; in 2.6 and onwards the bytes syntax can be used to refer to regular strings, to make portability easier (in Python 3, strings are Unicode by default). regards Steve -- Steve Holden +1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/ -- http://mail.python.org/mailman/listinfo/python-list
