GH-128520: Make pathlib._abc.WritablePath
a sibling of ReadablePath
#129014
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In the private pathlib ABCs, support write-only virtual filesystems by making
WritablePath
inherit directly fromJoinablePath
, rather than subclassingReadablePath
. There are two complications:Problem 1:
ReadablePath.open()
applies to both reading and writingSolution: a new
pathlib._abc.magic_open()
function replaces theopen()
method, which is dropped from the ABCs but remains inpathlib.Path
. The function works likeio.open()
, but additionally accepts objects with__open_rb__()
or__open_wb__()
methods as appropriate for the mode. These new dunders are made abstract methods ofReadablePath
andWritablePath
respectively. If the pathlib ABCs are made public, we could consider blessing an "openable" protocol and supporting it inio.open()
, removing the need forpathlib._abc.magic_open()
.Problem 2:
ReadablePath.copy
is secretly an object that supports the read side of copying, whereasWritablePath.copy
is a subclass additionally supporting the write sideSolution:
ReadablePath.copy
becomes a true method, whereasWritablePath.copy
is deleted. A newReadablePath._copy_reader
property provides aCopyReader
object, and similarlyWritablePath._copy_writer
is aCopyWriter
object. Once GH-125413 is resolved, we'll be able to move theCopyReader
functionality intoReadablePath.info
and eliminateReadablePath._copy_reader
.