ubelt.util_links module

Cross-platform logic for dealing with symlinks. Basic functionality should work on all operating systems including everyone’s favorite pathological OS (note that there is an additional helper file for this case), but there are some corner cases depending on your version. Recent versions of Windows tend to work, but there certain system settings that cause issues. Any POSIX system works without difficulty.

Example

>>> import ubelt as ub
>>> from os.path import normpath, join
>>> dpath = ub.Path.appdir('ubelt', normpath('demo/symlink')).ensuredir()
>>> real_path = dpath / 'real_file.txt'
>>> link_path = dpath / 'link_file.txt'
>>> ub.touch(real_path)
>>> result = ub.symlink(real_path, link_path, overwrite=True, verbose=3)
>>> parts = result.split(os.path.sep)
>>> print(parts[-1])
link_file.txt

ubelt.util_links.symlink(real_path, link_path, overwrite=False, verbose=0)

Create a link link_path that mirrors real_path.

This function attempts to create a real symlink, but will fall back on a hard link or junction if symlinks are not supported.

Parameters

• path (str | PathLike) – path to real file or directory

• link_path (str | PathLike) – path to desired location for symlink

• overwrite (bool, default=False) – overwrite existing symlinks. This will not overwrite real files on systems with proper symlinks. However, on older versions of windows junctions are indistinguishable from real files, so we cannot make this guarantee.

• verbose (int, default=0) – verbosity level

Returns

link path

Return type

str | PathLike

Note

On systems that do not contain support for symlinks (e.g. some versions / configurations of Windows), this function will fall back on hard links or junctions [WikiNTFSLinks], [WikiHardLink]. The differences between the two are explained in [WikiSymLink].

If symlinks are not available, then link_path and real_path must exist on the same filesystem. Given that, this function always works in the sense that (1) link_path will mirror the data from real_path, (2) updates to one will effect the other, and (3) no extra space will be used.

More details can be found in ubelt._win32_links. On systems that support symlinks (e.g. Linux), none of the above applies.

References

WikiSymLink

https://en.wikipedia.org/wiki/Symbolic_link

WikiHardLink

https://en.wikipedia.org/wiki/Hard_link

WikiNTFSLinks

https://en.wikipedia.org/wiki/NTFS_links

Example

>>> import ubelt as ub
>>> dpath = ub.Path.appdir('ubelt', 'test_symlink0').delete().ensuredir()
>>> real_path = (dpath / 'real_file.txt')
>>> link_path = (dpath / 'link_file.txt')
>>> real_path.write_text('foo')
>>> result = ub.symlink(real_path, link_path)
>>> assert ub.Path(result).read_text() == 'foo'
>>> dpath.delete()  # clenaup

Example

>>> import ubelt as ub
>>> from ubelt.util_links import _dirstats
>>> dpath = ub.Path.appdir('ubelt', 'test_symlink1').delete().ensuredir()
>>> _dirstats(dpath)
>>> real_dpath = (dpath / 'real_dpath').ensuredir()
>>> link_dpath = real_dpath.augment(stem='link_dpath')
>>> real_path = (dpath / 'afile.txt')
>>> link_path = (dpath / 'afile.txt')
>>> real_path.write_text('foo')
>>> result = ub.symlink(real_dpath, link_dpath)
>>> assert link_path.read_text() == 'foo', 'read should be same'
>>> link_path.write_text('bar')
>>> _dirstats(dpath)
>>> assert link_path.read_text() == 'bar', 'very bad bar'
>>> assert real_path.read_text() == 'bar', 'changing link did not change real'
>>> real_path.write_text('baz')
>>> _dirstats(dpath)
>>> assert real_path.read_text() == 'baz', 'very bad baz'
>>> assert link_path.read_text() == 'baz', 'changing real did not change link'
>>> ub.delete(link_dpath, verbose=1)
>>> _dirstats(dpath)
>>> assert not link_dpath.exists(), 'link should not exist'
>>> assert real_path.exists(), 'real path should exist'
>>> _dirstats(dpath)
>>> ub.delete(dpath, verbose=1)
>>> _dirstats(dpath)
>>> assert not real_path.exists()

Example

>>> # Specifying bad paths should error.
>>> import ubelt as ub
>>> import pytest
>>> dpath = ub.Path.appdir('ubelt', 'test_symlink2').ensuredir()
>>> real_path = dpath / 'real_file.txt'
>>> link_path = dpath / 'link_file.txt'
>>> real_path.write_text('foo')
>>> with pytest.raises(ValueError, match='link_path .* cannot be empty'):
>>>     ub.symlink(real_path, '')
>>> with pytest.raises(ValueError, match='real_path .* cannot be empty'):
>>>     ub.symlink('', link_path)