tail

[Barry Scott]

> On 7 May 2022, at 14:40, Stefan Ram <ram at zedat.fu-berlin.de> wrote:
> 
> Marco Sulla <Marco.Sulla.Python at gmail.com> writes:
>> So there's no way to reliably read lines in reverse in text mode using
>> seek and read, but the only option is readlines?
> 
>  I think, CPython is based on C. I don't know whether
>  Python's seek function directly calls C's fseek function,
>  but maybe the following parts of the C standard also are
>  relevant for Python?

There is the posix API that and the C FILE API.

I expect that the odities you about NUL chars is all about the FILE
API. As far as I know its the posix API that C Python uses and it
does not suffer from issues with binary files.

Barry

> 
> |Setting the file position indicator to end-of-file, as with
> |fseek(file, 0, SEEK_END), has undefined behavior for a binary
> |stream (because of possible trailing null characters) or for
> |any stream with state-dependent encoding that does not
> |assuredly end in the initial shift state.
> from a footnote in a draft of a C standard
> 
> |For a text stream, either offset shall be zero, or offset
> |shall be a value returned by an earlier successful call to
> |the ftell function on a stream associated with the same file
> |and whence shall be SEEK_SET.
> from a draft of a C standard
> 
> |A text stream is an ordered sequence of characters composed
> |into lines, each line consisting of zero or more characters
> |plus a terminating new-line character. Whether the last line
> |requires a terminating new-line character is implementation-defined.
> from a draft of a C standard
> 
>  This might mean that reading from a text stream that is not
>  ending in a new-line character might have undefined behavior
>  (depending on the C implementation). In practice, it might
>  mean that some things could go wrong near the end of such
>  a stream. 
> 
> 
> -- 
> https://mail.python.org/mailman/listinfo/python-list
>