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Re: Why does pathlib not have is_readable() & things like that?

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On 2016-04-26, Steven D'Aprano wrote:

> On Tue, 26 Apr 2016 11:30 pm, Adam Funk wrote:

>> I've been improvising with things like this:
>> 
>> import pathlib, os
>> 
>> path = pathlib.Path('some/directory')
>> writable = os.access(str(path), os.W_OK | os.X_OK)
>> 
>> Is that the best way to do it?
>
> No. All you have learned is that the directory is writable *now*. In a
> millisecond, or a minute, when you actually go to write to it, it may no
> longer be writable -- it may not even exist.
>
> There is a whole class of serious security vulnerabilities and bugs caused
> by the difference between the time you check something and the time you
> actually use it. "Time of check to time of use" bugs can be best avoided by
> not checking ahead of time whether the directory is writable, but just
> *attempting to write to it*, and catching the error if you can't.

I appreciate the general principle, but the situation here is a tool
that iterates over a loop of the following: GET some chunks of data
from a REST service, process them, PUT something back to existing
documents through the REST service, & save the result in a directory
specified as a command-line option.  I don't want the tool to modify
the first batch of data in the REST service, be unable to store the
results locally, & crash as a result.


-- 
A mathematical formula should never be "owned" by anybody! Mathematics
belongs to God.                                       --- Donald Knuth

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Why does pathlib not have is_readable() & things like that? Adam Funk <a24061@ducksburg.com> - 2016-04-26 14:30 +0100
  Re: Why does pathlib not have is_readable() & things like that? Random832 <random832@fastmail.com> - 2016-04-26 09:57 -0400
    Re: Why does pathlib not have is_readable() & things like that? Adam Funk <a24061@ducksburg.com> - 2016-04-28 14:02 +0100
      Re: Why does pathlib not have is_readable() & things like that? Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-04-28 16:24 +0300
      Re: Why does pathlib not have is_readable() & things like that? Grant Edwards <grant.b.edwards@gmail.com> - 2016-04-28 13:34 +0000
        Re: Why does pathlib not have is_readable() & things like that? Adam Funk <a24061@ducksburg.com> - 2016-04-29 10:49 +0100
          Re: Why does pathlib not have is_readable() & things like that? Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-04-29 14:51 +0300
            Re: Why does pathlib not have is_readable() & things like that? eryk sun <eryksun@gmail.com> - 2016-04-29 10:09 -0500
            Re: Why does pathlib not have is_readable() & things like that? Grant Edwards <grant.b.edwards@gmail.com> - 2016-04-29 23:53 +0000
  Re: Why does pathlib not have is_readable() & things like that? Steven D'Aprano <steve@pearwood.info> - 2016-04-27 01:46 +1000
    Re: Why does pathlib not have is_readable() & things like that? Adam Funk <a24061@ducksburg.com> - 2016-04-28 13:57 +0100

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