The above two cases are equivalent. But that's not the case for the
root directory. Unlike Unix, filesystem namespaces are implemented
directly on devices. For example, "//./C:" might resolve to a volume
device such as "\\Device\\HarddiskVolume2". With a trailing slash
added, "//./C:/" resolves to "\\Device\\HarddiskVolume2\\", which is
the root directory of the mounted filesystem on the volume.
Also, as a classic DOS path, "C:" without a trailing slash expands to
the working directory on drive "C:". The system runtime library looks
for this path in a hidden environment variable named "=C:". The
Windows API never sets these hidden "=X:" drive variables. The C
runtime sets them, as does Python's os.chdir.
Some volume-management functions require a trailing slash or
backslash, such as GetVolumeInformationW [1].
GetVolumeNameForVolumeMountPointW [2] actually requires it to be a
trailing backslash. It will not accept a trailing forward slash such
as "C:\\Mount\\Volume/" (a bug since Windows 2000). The volume name
(e.g. "\\\\?\\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}\\")
returned by the latter includes a trailing backslash, which must be
present in the target path in order for a mountpoint to function
properly as a directory, else it would resolve to the volume device
instead of the root directory.
[1] https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getvolumeinformationw
[2] https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getvolumenameforvolumemountpointw
If they're Windows developers, they ought to be aware that the Windows
file system API allows / anywhere you can use \ and it is the
common convention in Python to use forward slashes.
The Windows file API actually does not allow slash to be used anywhere
that we can use backslash. It's usually allowed, but not always. For
the most part, the conditions where forward slash is not supported are
intentional.
Windows replaces forward slash with backslash in normal DOS paths and
normal device paths. But sometimes we have to use a special form of
device path that bypasses normalization. A path that isn't normalized
can only use backslash as the path separator. For example, the most
common case is that the process doesn't have long paths enabled. In
this case we're limited to MAX_PATH, which limits file paths to a
paltry 259 characters (sans the terminating null); the current
directory to 258 characters (sans a trailing backslash and null); and
the path of a new directory to 247 characters (subtract 12 from 259 to
leave space for an 8.3 filename). By skipping DOS normalization, we
can access a path with up to about 32,750 characters (i.e. 32,767 sans
the length of the device name in the final NT path under
"\\Device\\").
(Long normalized paths are available starting in Windows 10, but the
system policy that allows this is disabled by default, and even if
enabled, each application has to declare itself to be long-path aware
in its manifest. This is declared for python[w].exe in Python 3.6+.)
A device path is an explicit reference to a user's local device
directory (in the object namespace), which shadows the global device
directory. In NT, this directory is aliased to a special "\\??\\"
prefix (backslash only). A local device directory is created for each
logon session (not terminal session) by the security system that runs
in terminal session 0 (i.e. the system services session). The
per-logon directory is located at "\\Sessions\\0\\DosDevices\\<Logon
Session ID>". In the Windows API, it's accessible as "//?/" or "//./",
or with any mix of forward slashes or backslashes, but only the
all-backslash form is special-cased to bypass the normalization step.
_______________________________________________
Python-Dev mailing list -- python-dev@python.org
To unsubscribe send an email to python-dev-leave@python.org
https://mail.python.org/mailman3/lists/python-dev.python.org/
Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/3SDFM2EKFO3UNTATS7KVBY2WOUTFMAF5/
---
This email has been checked for viruses by AVG.
https://www.avg.com