Add a `dir_fd` parameter to `os.truncate`?
Hi everyone, many methods in `os` have a `dir_fd` parameter, for instance `unlink` [1]: ```python os.unlink(path, *, dir_fd=None) ``` The `dir_fd` parameter [2] allows it to describe paths relative to directory descriptors. Otherwise, relative paths are relative to the current working directory. The implementation of `truncate` in `os` does not have this parameter [3]: ```python os.truncate(path, length) ``` On POSIX-like systems for instance, the `os` module actually imports [4] this function from the `posix module`. There, one can see that it [5] just calls the `truncate` system call [6]. This kind of implicitly explains why there is no `dir_fd` parameter: There is no such thing like a `truncateat` system call, which would be required for handling the `dir_fd` parameter [7, 8]. However, it is possible to work around this limitation: ```python def truncate(path, length, dir_fd = None): if dir_fd is None: return os.truncate(path, length) else: fd = os.open(path, flags = os.O_WRONLY, dir_fd = dir_fd) ret = os.ftruncate(fd, length) os.close(fd) return ret ``` Why not add a convenience function or wrapper like above to the `os` module, which closes this gap and is more consistent with other methods? Best regards, Sebastian [1] https://docs.python.org/3/library/os.html#os.unlink [2] https://docs.python.org/3/library/os.html#dir-fd [3] https://docs.python.org/3/library/os.html#os.truncate [4] https://github.com/python/cpython/blob/3.7/Lib/os.py#L135 [5] https://github.com/python/cpython/blob/3.7/Modules/posixmodule.c#L9042 [6] https://github.com/python/cpython/blob/3.7/Modules/posixmodule.c#L9079 [7] https://stackoverflow.com/q/52871892/1672565 [8] https://stackoverflow.com/q/55765181/1672565
On Fri, Apr 19, 2019 at 09:49:54PM +0200, Sebastian M. Ernst wrote:
[...]
Why not add a convenience function or wrapper like above to the `os` module, which closes this gap and is more consistent with other methods?
I haven't seen any responses to your proposal, perhaps I missed something. The os module is supposed to be a thin wrapper around the os functionality, but your wrapper seems thin enough that I think it could and should just go into the os.truncate function itself, rather than adding a new function. -- Steven
On Fri, Apr 19, 2019 at 09:49:54PM +0200, Sebastian M. Ernst wrote:
[...]
Why not add a convenience function or wrapper like above to the `os` module, which closes this gap and is more consistent with other methods?
I haven't seen any responses to your proposal, perhaps I missed something. The os module is supposed to be a thin wrapper around the os functionality, but your wrapper seems thin enough that I think it could and should just go into the os.truncate function itself, rather than adding a new function. -- Steven
participants (2)
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Sebastian M. Ernst -
Steven D'Aprano