How to clone files with Python?

Question

Using bash on macos I can create COW file clones with cp -c. Is there a Python library that provides the same functionality? The copy functions in shutil doesn't seem to mention cloning.

On APFS clones: https://developer.apple.com/library/content/documentation/FileManagement/Conceptual/APFS_Guide/Features/Features.html

On BSD clonefile: http://www.manpagez.com/man/2/clonefile/

https://stackoverflow.com/questions/123198/how-do-i-copy-a-file-in-python — Dylan Brams, Dec 22 '17 at 18:02
do you just need a cow buffer? in python this is typically referred to as `mmap` I haven't been able to find any information on cow files on osx... — Aaron, Dec 22 '17 at 18:09
I take it back, I just found an article talking about APFS adding cow (among other things...) — Aaron, Dec 22 '17 at 18:11
python does not seem to support the bsd `copyfile` command (which is what cp -c relies on), so you'll have to make system calls as Dylan suggested. — Aaron, Dec 22 '17 at 18:21
@DylanB This is clearly not a duplicate of the questions you have linked to, would you mind undoing marking this is as a duplicate. I feel like it was pretty clear in the question that I was referring to COW file clones. — antonagestam, Dec 22 '17 at 18:27

antonagestam · Accepted Answer · 2017-12-22T19:56:06.450

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The Python standard library does not support cloning files.

To clone a file using cp -c in a subprocess you can use this function:

def clonefile(source, dest):
    subprocess.check_output(["cp", "-c", source, dest])

edited Dec 22 '17 at 19:56

answered Dec 22 '17 at 18:34

antonagestam

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score -1 · Answer 2 · answered Dec 22 '17 at 18:07

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Ok, I marked this as a duplicate but didn't know the difference between copying and cloning.

This is the location of the instructions for copying files with as much detail as possible in Python: https://docs.python.org/3.6/library/shutil.html

It starts with the following warning: Warning Even the higher-level file copying functions (shutil.copy(), shutil.copy2()) cannot copy all file metadata.

If what you want is an OS cloning of the file, you're going to need to run a system call. That system call is going to need to be OS specific, and the call will be pulled from this question: Calling an external command in Python

So, look into the copy library and see if you can get enough detail, and if you can't use a system-specific call.

answered Dec 22 '17 at 18:07

Dylan Brams

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your reference to external commands may be useful, but the OP already covered that `shutil` is not an acceptable solution. – Aaron Dec 22 '17 at 18:16
All the documentation I found pointed to shutil being as deep as Python goes.... I was a bit trigger happy on the answer, I admit. – Dylan Brams Dec 22 '17 at 18:21
And, bluntly, it wouldn't make much sense for Python to have standard libraries system-specific enough to keep up with the power of Bash, ksh, etc. A compiled solution would need to do all sorts of system lookups and (potentially bug ridden) dancing to keep up. So I'd say you're better off sticking with the tool that does what you specifically need. – Dylan Brams Dec 22 '17 at 18:27

How to clone files with Python?

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