[Python-Dev] My summary of the scandir (PEP 471)

[Victor Stinner]

Hi,

@Ben: it's time to update your PEP to complete it with this
discussion! IMO DirEntry must be as simple as possible and portable:

- os.scandir(str)
- DirEntry.lstat_result object only available on Windows, same result
than os.lstat()
- DirEntry.fullname(): os.path.join(directory, DirEntry.name), where
directory would be an hidden attribute of DirEntry


Notes:

- DirEntry.lstat_result is better than DirEntry.lstat() because it
makes explicitly that lstat_result is only computed once. When I call
DirEntry.lstat(), I expect to get the current status of the file, not
the cached one. It's also hard to explain (document) that
DirEntry.lstat() may or may call a system call. Don't do that, use
DirEntry.lstat_result.

- I don't think that we should support scandir(bytes). If you really
want to support os.scandir(bytes), it must raise an error on Windows
since bytes filename are already deprecated. It wouldn't make sense to
add new function with a deprecated feature. Since we have the PEP 383
(surrogateescape), it's better to advice to use Unicode on all
platforms. Almost all Python functions are able to encode back Unicode
filename automatically. Use os.fsencode() to encode manually if needd.

- We may not define a DirEntry.fullname() method: the directory name
is usually well known. Ok, but every time that I use os.listdir(), I
write os.path.join(directory, name) because in some cases I want the
full path. Example:

interesting = []
for name in os.listdir(path):
   fullpath = os.path.join(path, name)
   if os.path.isdir(fullpath):
      continue
   if ... test on the file ...:
      # i need the full path here, not the relative path
      # (ex: my own recursive "scandir"/"walk" function)
      interesting.append(fullpath)

- It must not be possible to "refresh" a DirEntry object. Call
os.stat(entry.fullname()) or pathlib.Path(entry.fullname()) to get
fresh data. DirEntry is only computed once, that's all. It's well
defined.

- No Windows wildcard, you wrote that the feature has many corner
cases, and it's only available on Windows. It's easy to combine
scandir with fnmatch.

Victor