How do I converted a null (0) terminated string to a Python string?

[John Machin]

Michael top-posted [again]:
>
> John Machin wrote:
> > Michael top-posted [corrected]:
> > > John Machin wrote:
> > > > Michael wrote:
> > > > > Hi All,
> > > > >
> > > > > I've received (via UDP) a null terminated string and need to convert it
> > > > > into a Python string. Can anyone tell me how this is done? If it helps,
> > > > > I know the number of characters in the string.
> > > > >
> > > >
> > > > I think you mean NUL, not null.
> > > >
> > > > What have you received it into, if it's not a Python string?
> > > >
> > > > You probably need/want this:
> > > >
> > > > if strg[-1] == "\0":
> > > >     strg = strg[:-1]
> > > > alternatively:
> > > > strg = strg.rstrip("\0") # requires Python 2.2.2 or later
> > > >
> > > > It's possible you may be talking about a fixed length string which
> > > > contains useful_stuff + "\0" + padding -- in that case you need
> > > >
> > > > strg = strg.split("\0")[0] # grab upto (but not including) the first
> > > > NUL (if any)
> > > >
> > > > If you're not sure what you've got, print repr(the_input_string)
> > > >
> > > > HTH,
> > > > John
> > > Thank you very much for your responses. To answer some of the
> > > questions... Yes, I am in Python receiving a C language 0 terminated
> > > string that was sent to my Python program in a UDP packet (which is how
> > > I know the count). Are your responses still correct given this
> > > clarification?
> >
> > My responses are correct. Your "clarification" indicates to me that you
> > are going by what you are told, not by inspection of (several instances
> > of) the packet contents, using repr(). It's up to you whether you want
> > to be skeptical about the packet contents or not. I certainly wouldn't
> > be throwing the last byte away without checking that it was in fact a
> > NUL.
> >
> > Cheers,
> > John
> John,
>
> Thanks for your reply. Just wondering... how are Python strings
> formatted? Evidently they're not 0 terminated.

A Python string is an object. The details of the internal storage may
vary between implementations. CPython  has 8-bit str objects and 16-bit
or 32-bit Unicode objects. In IronPython, (str is Unicode) is true, and
they are 16 bits. In any case the object knows its own length without
having to scan for a terminator. Thus, a string can contain NULs.

Having said all that, the CPython str implementation does have an
additional byte at the end; this is set to zero and is not counted in
the length. However you never see that and don't really need to know
unless you are writing an extension module in C -- it's handy to know
that you don't have to append a NUL if you want to call a C library
function.

Cheers,
John