How to construct an in-memory virtual file system and then write this structure to disk

Question

I'm looking for a way to create a virtual file system in Python for creating directories and files, before writing these directories and files to disk.

Using PyFilesystem I can construct a memory filesystem using the following:

>>> import fs
>>> temp_dir = fs.open_fs('mem://')
>>> temp_dir.makedirs('fruit')
SubFS(MemoryFS(), '/fruit')
>>> temp_dir.makedirs('vegetables')
SubFS(MemoryFS(), '/vegetables')
>>> with temp_dir.open('fruit/apple.txt', 'w') as apple: apple.write('braeburn')
... 
8
>>> temp_dir.tree()
├── fruit
│   └── apple.txt
└── vegetables

Ideally, I want to be able to do something like:

temp_dir.write_to_disk('<base path>')

To write this structure to disk, where <base path> is the parent directory in which this structure will be created.

As far as I can tell, PyFilesystem has no way of achieving this. Is there anything else I could use instead or would I have to implement this myself?

Bechtold

Answer 1

You can use fs.copy.copy_fs() to copy from one filesystem to another, or fs.move.move_fs() to move the filesystem altogether.

Given that PyFilesystem also abstracts around the underlying system filesystem - OSFS - in fact, it's the default protocol, all you need is to copy your in-memory filesystem (MemoryFS) to it and, in effect, you'll have it written to the disk:

import fs
import fs.copy

mem_fs = fs.open_fs('mem://')
mem_fs.makedirs('fruit')
mem_fs.makedirs('vegetables')
with mem_fs.open('fruit/apple.txt', 'w') as apple:
    apple.write('braeburn')

# write to the CWD for testing...
with fs.open_fs(".") as os_fs:  # use a custom path if you want, i.e. osfs://<base_path>
    fs.copy.copy_fs(mem_fs, os_fs)

Wollongong

Good answer. copy_fs accepts FS objects and FS URLs, so the following would also work: fs.copy.copy_fs(mem_fs, '.') – Fagot

Answer 2

If you just want to stage a file system tree in memory, look at the tarfile module.

Creating files and directories is a bit involved:

tarblob = io.BytesIO()
tar = tarfile.TarFile(mode="w", fileobj=tarblob)
dirinfo = tarfile.TarInfo("directory")
dirinfo.mode = 0o755
dirinfo.type = tarfile.DIRTYPE
tar.addfile(dirinfo, None)

filedata = io.BytesIO(b"Hello, world!\n")
fileinfo = tarfile.TarInfo("directory/file")
fileinfo.size = len(filedata.getbuffer())
tar.addfile(fileinfo, filedata)
tar.close()

But then you can create the file system hierarchy using TarFile.extractall:

tarblob.seek(0) # Rewind to the beginning of the buffer.
tar = tarfile.TarFile(mode="r", fileobj=tarblob)
tar.extractall()

Lauryn