Re: File opening modes (r, w, a ...)

[jfong]

Lew Pitcher於 2018年2月23日星期五 UTC+8上午9時43分19秒寫道：
> jf...@ms4.hinet.net wrote:
> 
> > ast於 2018年2月22日星期四 UTC+8下午8時33分00秒寫道：
> >> Hello
> >> 
> >> I share a very valuable table I found on
> >> StackOverflow about file opening modes
> >> 
> >> If like me you always forget the details of
> >> file opening mode, the following table provides
> >> a good summary
> >> 
> >>| r   r+   w   w+   a   a+
> >> --|--
> >> read  | +   +++
> >> write | ++   ++   +
> >> write after seek  | ++   +
> >> create|  +   ++   +
> >> truncate  |  +   +
> >> position at start | +   ++   +
> >> position at end   |   +   +
> > 
> > What the "write after seek" means?
> 
> It /should/ mean that programs are permitted to seek to a point in the file, 
> and then write from that point on.
> 
> A write to a read mode ("r") file isn't permitted at all,
> so neither is "write after seek" to a read mode file.
> 
> A write to an append mode ("a" and "a+") file always write to the end of the 
> file, effectively negating any seek.
> 
> HTH
> 
> -- 
> Lew Pitcher
> "In Skills, We Trust"
> PGP public key available upon request

Thank you for explanation.

Mode 'r+', 'a' and 'a+' all can be seek and write, but only 'r+' was marked in 
the table. That's why I was confused. This row seems redundant to me:-)

--Jach
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https://mail.python.org/mailman/listinfo/python-list

Re: File opening modes (r, w, a ...)

[Lew Pitcher]

jf...@ms4.hinet.net wrote:

> ast於 2018年2月22日星期四 UTC+8下午8時33分00秒寫道：
>> Hello
>> 
>> I share a very valuable table I found on
>> StackOverflow about file opening modes
>> 
>> If like me you always forget the details of
>> file opening mode, the following table provides
>> a good summary
>> 
>>| r   r+   w   w+   a   a+
>> --|--
>> read  | +   +++
>> write | ++   ++   +
>> write after seek  | ++   +
>> create|  +   ++   +
>> truncate  |  +   +
>> position at start | +   ++   +
>> position at end   |   +   +
> 
> What the "write after seek" means?

It /should/ mean that programs are permitted to seek to a point in the file, 
and then write from that point on.

A write to a read mode ("r") file isn't permitted at all,
so neither is "write after seek" to a read mode file.

A write to an append mode ("a" and "a+") file always write to the end of the 
file, effectively negating any seek.

HTH

-- 
Lew Pitcher
"In Skills, We Trust"
PGP public key available upon request

-- 
https://mail.python.org/mailman/listinfo/python-list

Re: File opening modes (r, w, a ...)

[jfong]

ast於 2018年2月22日星期四 UTC+8下午8時33分00秒寫道：
> Hello
> 
> I share a very valuable table I found on
> StackOverflow about file opening modes
> 
> If like me you always forget the details of
> file opening mode, the following table provides
> a good summary
> 
>| r   r+   w   w+   a   a+
> --|--
> read  | +   +++
> write | ++   ++   +
> write after seek  | ++   +
> create|  +   ++   +
> truncate  |  +   +
> position at start | +   ++   +
> position at end   |   +   +

What the "write after seek" means?

--Jach
-- 
https://mail.python.org/mailman/listinfo/python-list

Re: File opening modes (r, w, a ...)

[Steven D'Aprano]

On Thu, 22 Feb 2018 13:32:45 +0100, ast wrote:

> Hello
> 
> I share a very valuable table I found on StackOverflow about file
> opening modes
> 
> If like me you always forget the details of file opening mode, the
> following table provides a good summary

Thanks!



-- 
Steve

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