[Python-ideas] Context helper for new os.*at functions

[Guido van Rossum]

Hmm... Isn't Larry Hastings working on replacing the separate
functions with an api where you pass an 'fd=...' argument to the
non-at function?

On Sat, Jun 16, 2012 at 5:13 PM, Christian Heimes <lists at cheimes.de> wrote:
> Hello,
>
> Python 3.3 has got new wrappers for the 'at' variants of low level
> functions, for example os.openat(). The 'at' variants work like their
> brothers and sisters with one exception. The first argument must be a
> file descriptor of a directory. The fd is used to calculate the absolute
> path instead of the current working directory.
>
> File descriptors are harder to manage than files because a fd isnt't
> automatically closed when it gets out of scope. I've written a small
> wrapper that takes care of the details. It also ensures that only
> directories are opened.
>
> Example:
>
> with atcontext("/etc") as at:
>    print(at.open)
>    # functools.partial(<built-in function openat>, 3)
>    f = at.open("fstab", os.O_RDONLY)
>    print(os.read(f, 50))
>    os.close(f)
>
> Code:
> http://pastebin.com/J4SLjB6k
>
> The code calculates the name and creates dynamic wrapper with
> functool.partial. This may not be desired if the wrapper is added to the
> os module. I could add explicit methods and generate the doc strings
> from the methods' doc strings.
>
> def docfix(func):
>    name = func.__name__
>    nameat = name + "at"
>    doc = getattr(os, nameat).__doc__
>    func.__doc__ = doc.replace("{}(dirfd, ".format(nameat),
>                               "{}(".format(name))
>    return func
>
> class atcontext:
>    ...
>
>    @docfix
>    def open(self, *args):
>        return self.openat(self.dirf, *args)
>
>
> How do you like my proposal?
>
> Christian
>
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-- 
--Guido van Rossum (python.org/~guido)