Context helper for new os.*at functions
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
Am 17.06.2012 02:46, schrieb Guido van Rossum:
Oh, is he? I didn't know that. Indeed, it sounds like a good approach. Users must still handle the fd correctly and make sure they open a directory. Linux's man(2) open warns about possibility of denial-of-service attempts for wrong fds. Linux has O_DIRECTORY for this purpose. On other OSes users should do a stat() call in front, which is open for race conditions but still better than getting stuck in a FIFO. I could modify the wrapper a bit to make the wrapper useful for the new API: class atcontext: def fileno(self): # for PyObject_AsFileDescriptor() return self.dirfd with atcontext("/etc") as at: os.open("fstab", os.O_RDONLY, fd=at) Christian
Am 17.06.2012 02:46, schrieb Guido van Rossum:
Oh, is he? I didn't know that. Indeed, it sounds like a good approach. Users must still handle the fd correctly and make sure they open a directory. Linux's man(2) open warns about possibility of denial-of-service attempts for wrong fds. Linux has O_DIRECTORY for this purpose. On other OSes users should do a stat() call in front, which is open for race conditions but still better than getting stuck in a FIFO. I could modify the wrapper a bit to make the wrapper useful for the new API: class atcontext: def fileno(self): # for PyObject_AsFileDescriptor() return self.dirfd with atcontext("/etc") as at: os.open("fstab", os.O_RDONLY, fd=at) Christian
participants (2)
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Christian Heimes -
Guido van Rossum