From 0a4f60a77e85af697d536717454a101cadc870d3 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 1 Feb 2024 08:08:35 +0000
Subject: [PATCH 01/17] GH-114847: Speed up `posixpath.realpath()`

Apply the following optimizations to `posixpath.realpath()`:

- Remove use of recursion
- Directly construct child paths rather than using `join()`
- Use `os.getcwd[b]()` rather than `abspath()`
- Use `startswith(sep)` rather than `isabs()`
---
 Lib/posixpath.py                              | 83 +++++++++++--------
 ...-02-01-08-09-20.gh-issue-114847.-JrWrR.rst |  1 +
 2 files changed, 49 insertions(+), 35 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2024-02-01-08-09-20.gh-issue-114847.-JrWrR.rst

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index e4f155e41a3221..91e256f72a1103 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -432,49 +432,46 @@ def realpath(filename, *, strict=False):
     """Return the canonical path of the specified filename, eliminating any
 symbolic links encountered in the path."""
     filename = os.fspath(filename)
-    path, ok = _joinrealpath(filename[:0], filename, strict, {})
-    return abspath(path)
-
-# Join two paths, normalizing and eliminating any symbolic links
-# encountered in the second path.
-def _joinrealpath(path, rest, strict, seen):
-    if isinstance(path, bytes):
+    if isinstance(filename, bytes):
         sep = b'/'
         curdir = b'.'
         pardir = b'..'
+        getcwd = os.getcwdb
     else:
         sep = '/'
         curdir = '.'
         pardir = '..'
-
-    if isabs(rest):
-        rest = rest[1:]
-        path = sep
-
-    while rest:
-        name, _, rest = rest.partition(sep)
+        getcwd = os.getcwd
+
+    seen = {}
+    stack = []
+    querying = True
+    path = sep if filename.startswith(sep) else getcwd()
+    for part in reversed(filename.split(sep)):
+        stack.append((False, part))
+
+    while stack:
+        is_symlink, name = stack.pop()
+        if is_symlink:
+            # resolved symlink
+            seen[name] = path
+            continue
         if not name or name == curdir:
             # current dir
             continue
         if name == pardir:
             # parent dir
-            if path:
-                path, name = split(path)
-                if name == pardir:
-                    path = join(path, pardir, pardir)
+            newpath, name = split(path)
+            if name == pardir:
+                path = path + sep + pardir
             else:
-                path = pardir
+                path = newpath
             continue
-        newpath = join(path, name)
-        try:
-            st = os.lstat(newpath)
-        except OSError:
-            if strict:
-                raise
-            is_link = False
+        if len(path) == 1:
+            newpath = path + name
         else:
-            is_link = stat.S_ISLNK(st.st_mode)
-        if not is_link:
+            newpath = path + sep + name
+        if not querying:
             path = newpath
             continue
         # Resolve the symbolic link
@@ -490,14 +487,30 @@ def _joinrealpath(path, rest, strict, seen):
                 os.stat(newpath)
             else:
                 # Return already resolved part + rest of the path unchanged.
-                return join(newpath, rest), False
-        seen[newpath] = None # not resolved symlink
-        path, ok = _joinrealpath(path, os.readlink(newpath), strict, seen)
-        if not ok:
-            return join(path, rest), False
-        seen[newpath] = path # resolved symlink
+                path = newpath
+                querying = False
+            continue
+        try:
+            st = os.lstat(newpath)
+            if not stat.S_ISLNK(st.st_mode):
+                path = newpath
+                continue
+            target = os.readlink(newpath)
+        except OSError:
+            if strict:
+                raise
+            else:
+                path = newpath
+                querying = False
+                continue
 
-    return path, True
+        seen[newpath] = None # not resolved symlink
+        if target.startswith(sep):
+            path = sep
+        stack.append((True, newpath))
+        for part in reversed(target.split(sep)):
+            stack.append((False, part))
+    return path
 
 
 supports_unicode_filenames = (sys.platform == 'darwin')
diff --git a/Misc/NEWS.d/next/Library/2024-02-01-08-09-20.gh-issue-114847.-JrWrR.rst b/Misc/NEWS.d/next/Library/2024-02-01-08-09-20.gh-issue-114847.-JrWrR.rst
new file mode 100644
index 00000000000000..bf011fed3efdbc
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-02-01-08-09-20.gh-issue-114847.-JrWrR.rst
@@ -0,0 +1 @@
+Speed up :func:`os.path.realpath` on non-Windows platforms.

From 5aa9c51dc5ed69ea3c624839a8ed7430cef7299e Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 1 Feb 2024 08:31:23 +0000
Subject: [PATCH 02/17] Tiny tweak

---
 Lib/posixpath.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 91e256f72a1103..63d95fc0f6948d 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -467,7 +467,7 @@ def realpath(filename, *, strict=False):
             else:
                 path = newpath
             continue
-        if len(path) == 1:
+        if path == sep:
             newpath = path + name
         else:
             newpath = path + sep + name

From b7587109db4d1c2e47e4b75901c01477a1427f94 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 1 Feb 2024 08:35:43 +0000
Subject: [PATCH 03/17] Slightly speed up handling of empty/dot parts

---
 Lib/posixpath.py | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 63d95fc0f6948d..504a05ee9987ab 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -448,7 +448,8 @@ def realpath(filename, *, strict=False):
     querying = True
     path = sep if filename.startswith(sep) else getcwd()
     for part in reversed(filename.split(sep)):
-        stack.append((False, part))
+        if part and part != curdir:
+            stack.append((False, part))
 
     while stack:
         is_symlink, name = stack.pop()
@@ -456,9 +457,6 @@ def realpath(filename, *, strict=False):
             # resolved symlink
             seen[name] = path
             continue
-        if not name or name == curdir:
-            # current dir
-            continue
         if name == pardir:
             # parent dir
             newpath, name = split(path)
@@ -509,7 +507,8 @@ def realpath(filename, *, strict=False):
             path = sep
         stack.append((True, newpath))
         for part in reversed(target.split(sep)):
-            stack.append((False, part))
+            if part and part != curdir:
+                stack.append((False, part))
     return path
 
 

From 60d3bcb0d7af66efe64bde861b712f6e411a8147 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sun, 31 Mar 2024 19:38:16 +0100
Subject: [PATCH 04/17] Simplify '..' handling.

---
 Lib/posixpath.py | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 186acc3a999a8c..29d50cd46169e8 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -439,11 +439,7 @@ def realpath(filename, *, strict=False):
             continue
         if name == pardir:
             # parent dir
-            newpath, name = split(path)
-            if name == pardir:
-                path = path + sep + pardir
-            else:
-                path = newpath
+            path = dirname(path)
             continue
         if path == sep:
             newpath = path + name

From b8493081b9fef2e066c1829daae1ef2a33213bcc Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sun, 31 Mar 2024 19:55:06 +0100
Subject: [PATCH 05/17] A few more perf improvements and simplifications.

---
 Lib/posixpath.py | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 29d50cd46169e8..1fcd7c2c384704 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -424,12 +424,9 @@ def realpath(filename, *, strict=False):
         getcwd = os.getcwd
 
     seen = {}
-    stack = []
-    querying = True
     path = sep if filename.startswith(sep) else getcwd()
-    for part in reversed(filename.split(sep)):
-        if part and part != curdir:
-            stack.append((False, part))
+    stack = [(False, part) for part in reversed(filename.split(sep))]
+    querying = True
 
     while stack:
         is_symlink, name = stack.pop()
@@ -437,17 +434,22 @@ def realpath(filename, *, strict=False):
             # resolved symlink
             seen[name] = path
             continue
+        if not name or name == curdir:
+            # current dir
+            continue
         if name == pardir:
             # parent dir
-            path = dirname(path)
+            path = path[:path.rfind(sep)] or sep
             continue
         if path == sep:
             newpath = path + name
         else:
             newpath = path + sep + name
+
         if not querying:
             path = newpath
             continue
+
         # Resolve the symbolic link
         if newpath in seen:
             # Already seen this path
@@ -482,9 +484,7 @@ def realpath(filename, *, strict=False):
         if target.startswith(sep):
             path = sep
         stack.append((True, newpath))
-        for part in reversed(target.split(sep)):
-            if part and part != curdir:
-                stack.append((False, part))
+        stack.extend((False, part) for part in reversed(target.split(sep)))
     return path
 
 

From 085e1050ccaa0c0ab2dd02ca88794f727a2c90d4 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sun, 31 Mar 2024 20:08:11 +0100
Subject: [PATCH 06/17] Simplify symlink resolution signalling

---
 Lib/posixpath.py | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 1fcd7c2c384704..795a2f5e60f9ac 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -423,16 +423,16 @@ def realpath(filename, *, strict=False):
         pardir = '..'
         getcwd = os.getcwd
 
-    seen = {}
     path = sep if filename.startswith(sep) else getcwd()
-    stack = [(False, part) for part in reversed(filename.split(sep))]
+    rest = filename.split(sep)[::-1]
+    seen = {}
     querying = True
 
-    while stack:
-        is_symlink, name = stack.pop()
-        if is_symlink:
+    while rest:
+        name = rest.pop()
+        if name is None:
             # resolved symlink
-            seen[name] = path
+            seen[rest.pop()] = path
             continue
         if not name or name == curdir:
             # current dir
@@ -445,11 +445,9 @@ def realpath(filename, *, strict=False):
             newpath = path + name
         else:
             newpath = path + sep + name
-
         if not querying:
             path = newpath
             continue
-
         # Resolve the symbolic link
         if newpath in seen:
             # Already seen this path
@@ -483,8 +481,9 @@ def realpath(filename, *, strict=False):
         seen[newpath] = None # not resolved symlink
         if target.startswith(sep):
             path = sep
-        stack.append((True, newpath))
-        stack.extend((False, part) for part in reversed(target.split(sep)))
+        rest.append(newpath)
+        rest.append(None)
+        rest.extend(target.split(sep)[::-1])
     return path
 
 

From 69dabd2aa0860476e27f3a899e7f4e633dae0784 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sun, 31 Mar 2024 20:39:20 +0100
Subject: [PATCH 07/17] Tiny tweaks

---
 Lib/posixpath.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 795a2f5e60f9ac..f02f83766fc48d 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -423,7 +423,7 @@ def realpath(filename, *, strict=False):
         pardir = '..'
         getcwd = os.getcwd
 
-    path = sep if filename.startswith(sep) else getcwd()
+    path = sep if filename[:1] == sep else getcwd()
     rest = filename.split(sep)[::-1]
     seen = {}
     querying = True
@@ -463,7 +463,7 @@ def realpath(filename, *, strict=False):
                 # Return already resolved part + rest of the path unchanged.
                 path = newpath
                 querying = False
-            continue
+                continue
         try:
             st = os.lstat(newpath)
             if not stat.S_ISLNK(st.st_mode):
@@ -479,7 +479,7 @@ def realpath(filename, *, strict=False):
                 continue
 
         seen[newpath] = None # not resolved symlink
-        if target.startswith(sep):
+        if target[:1] == sep:
             path = sep
         rest.append(newpath)
         rest.append(None)

From 197c871edeec082fca9c152a8ddadf1c91bb8d6e Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Sun, 31 Mar 2024 20:40:44 +0100
Subject: [PATCH 08/17] Spacing

---
 Lib/posixpath.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index f02f83766fc48d..06c88a0062ad57 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -477,13 +477,13 @@ def realpath(filename, *, strict=False):
                 path = newpath
                 querying = False
                 continue
-
         seen[newpath] = None # not resolved symlink
         if target[:1] == sep:
             path = sep
         rest.append(newpath)
         rest.append(None)
         rest.extend(target.split(sep)[::-1])
+
     return path
 
 

From ecd1fe7157e729a84d91a5bb5bd81fd413235a5c Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Mon, 1 Apr 2024 22:26:25 +0100
Subject: [PATCH 09/17] Comments

---
 Lib/posixpath.py | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 06c88a0062ad57..1bfe95c245573a 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -423,15 +423,27 @@ def realpath(filename, *, strict=False):
         pardir = '..'
         getcwd = os.getcwd
 
-    path = sep if filename[:1] == sep else getcwd()
+    # The stack of unresolved path parts.
     rest = filename.split(sep)[::-1]
+
+    # The resolved path, which is absolute throughout this function.
+    # Note: getcwd() returns a normalized and symlink-free path.
+    path = sep if filename[:1] == sep else getcwd()
+
+    # Mapping from symlink paths to *fully resolved* symlink targets. If a
+    # symlink is encountered but not yet resolved, the value is None. This is
+    # used both to detect symlink loops and to speed up repeated traversals of
+    # the same links.
     seen = {}
+
+    # Whether we're calling lstat() and readlink() to resolve symlinks. If we
+    # encounter an OSError in non-strict mode, this is switched off.
     querying = True
 
     while rest:
         name = rest.pop()
         if name is None:
-            # resolved symlink
+            # resolved symlink target
             seen[rest.pop()] = path
             continue
         if not name or name == curdir:
@@ -474,14 +486,20 @@ def realpath(filename, *, strict=False):
             if strict:
                 raise
             else:
+                # Return already resolved part + rest of the path unchanged.
                 path = newpath
                 querying = False
                 continue
-        seen[newpath] = None # not resolved symlink
         if target[:1] == sep:
+            # Symlink target is absolute; reset resolved path.
             path = sep
+        seen[newpath] = None # not resolved symlink
+        # Push the symlink path onto the stack, and signal its specialness by
+        # also pushing None. When these entries are popped, we'll record the
+        # fully-resolved symlink target in the 'seen' mapping .
         rest.append(newpath)
         rest.append(None)
+        # Push the unresolved symlink target parts onto the stack.
         rest.extend(target.split(sep)[::-1])
 
     return path

From 4b83c97fa32fed7ce292b043f9fefdf67410c8dc Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Mon, 1 Apr 2024 22:39:32 +0100
Subject: [PATCH 10/17] Final tweaks

---
 Lib/posixpath.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 1bfe95c245573a..343cb1e5ff2aa0 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -428,7 +428,7 @@ def realpath(filename, *, strict=False):
 
     # The resolved path, which is absolute throughout this function.
     # Note: getcwd() returns a normalized and symlink-free path.
-    path = sep if filename[:1] == sep else getcwd()
+    path = sep if filename.startswith(sep) else getcwd()
 
     # Mapping from symlink paths to *fully resolved* symlink targets. If a
     # symlink is encountered but not yet resolved, the value is None. This is
@@ -490,13 +490,13 @@ def realpath(filename, *, strict=False):
                 path = newpath
                 querying = False
                 continue
-        if target[:1] == sep:
+        if target.startswith(sep):
             # Symlink target is absolute; reset resolved path.
             path = sep
         seen[newpath] = None # not resolved symlink
         # Push the symlink path onto the stack, and signal its specialness by
         # also pushing None. When these entries are popped, we'll record the
-        # fully-resolved symlink target in the 'seen' mapping .
+        # fully-resolved symlink target in the 'seen' mapping.
         rest.append(newpath)
         rest.append(None)
         # Push the unresolved symlink target parts onto the stack.

From 77712d2fccd83f0f748ea76c77ddd2a8005c7fb5 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Tue, 2 Apr 2024 00:13:41 +0100
Subject: [PATCH 11/17] Further explain 'rest'.

---
 Lib/posixpath.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 343cb1e5ff2aa0..4bdcbfa23f9586 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -423,7 +423,10 @@ def realpath(filename, *, strict=False):
         pardir = '..'
         getcwd = os.getcwd
 
-    # The stack of unresolved path parts.
+    # The stack of unresolved path parts. When popped, a special value of None
+    # indicates that a symlink target has been resolved, and that the original
+    # symlink path can be retrieved by popping again. The [::-1] slice is a
+    # very fast way of spelling list(reversed(...)).
     rest = filename.split(sep)[::-1]
 
     # The resolved path, which is absolute throughout this function.

From 15199a87c55cf22d2b88f3068ec1d079a0357d05 Mon Sep 17 00:00:00 2001
From: Barney Gale <barney.gale@gmail.com>
Date: Tue, 2 Apr 2024 20:42:07 +0100
Subject: [PATCH 12/17] Update Lib/posixpath.py

Co-authored-by: Petr Viktorin <encukou@gmail.com>
---
 Lib/posixpath.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 4bdcbfa23f9586..ef9038d23a1d6c 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -454,7 +454,7 @@ def realpath(filename, *, strict=False):
             continue
         if name == pardir:
             # parent dir
-            path = path[:path.rfind(sep)] or sep
+            path = path[:path.rindex(sep)] or sep
             continue
         if path == sep:
             newpath = path + name

From 31955eead612107c8ec350fac8a5f8a03349ffe6 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Wed, 3 Apr 2024 20:21:56 +0100
Subject: [PATCH 13/17] Undo re-ordering of lstat() and seen lookup

---
 Lib/posixpath.py | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 89136afa4e5816..14c552158a2250 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -454,6 +454,17 @@ def realpath(filename, *, strict=False):
         if not querying:
             path = newpath
             continue
+        try:
+            st = os.lstat(newpath)
+        except OSError:
+            if strict:
+                raise
+            is_link = False
+        else:
+            is_link = stat.S_ISLNK(st.st_mode)
+        if not is_link:
+            path = newpath
+            continue
         # Resolve the symbolic link
         if newpath in seen:
             # Already seen this path
@@ -470,24 +481,11 @@ def realpath(filename, *, strict=False):
                 path = newpath
                 querying = False
                 continue
-        try:
-            st = os.lstat(newpath)
-            if not stat.S_ISLNK(st.st_mode):
-                path = newpath
-                continue
-            target = os.readlink(newpath)
-        except OSError:
-            if strict:
-                raise
-            else:
-                # Return already resolved part + rest of the path unchanged.
-                path = newpath
-                querying = False
-                continue
+        seen[newpath] = None # not resolved symlink
+        target = os.readlink(newpath)
         if target.startswith(sep):
             # Symlink target is absolute; reset resolved path.
             path = sep
-        seen[newpath] = None # not resolved symlink
         # Push the symlink path onto the stack, and signal its specialness by
         # also pushing None. When these entries are popped, we'll record the
         # fully-resolved symlink target in the 'seen' mapping.

From fe62fef0050638c6de40475fd0d353f10bd981e6 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 4 Apr 2024 01:37:44 +0100
Subject: [PATCH 14/17] Re-optimise link check

---
 Lib/posixpath.py | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 14c552158a2250..ad895de3935b27 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -456,13 +456,12 @@ def realpath(filename, *, strict=False):
             continue
         try:
             st = os.lstat(newpath)
+            if not stat.S_ISLNK(st.st_mode):
+                path = newpath
+                continue
         except OSError:
             if strict:
                 raise
-            is_link = False
-        else:
-            is_link = stat.S_ISLNK(st.st_mode)
-        if not is_link:
             path = newpath
             continue
         # Resolve the symbolic link

From ebccd2bbd8d8c349c8a098e729b3e76653e59f3f Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 4 Apr 2024 01:43:19 +0100
Subject: [PATCH 15/17] Stop querying when `lstat()` fails.

---
 Lib/posixpath.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index ad895de3935b27..d9005ecfeb5786 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -463,6 +463,7 @@ def realpath(filename, *, strict=False):
             if strict:
                 raise
             path = newpath
+            querying = False
             continue
         # Resolve the symbolic link
         if newpath in seen:

From d2a024803aac420755071ba90e6e597af2065082 Mon Sep 17 00:00:00 2001
From: barneygale <barney.gale@gmail.com>
Date: Thu, 4 Apr 2024 14:11:28 +0100
Subject: [PATCH 16/17] Keep querying if we hit an OSError from lstat()

---
 Lib/posixpath.py           | 1 -
 Lib/test/test_posixpath.py | 9 +++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index d9005ecfeb5786..ad895de3935b27 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -463,7 +463,6 @@ def realpath(filename, *, strict=False):
             if strict:
                 raise
             path = newpath
-            querying = False
             continue
         # Resolve the symbolic link
         if newpath in seen:
diff --git a/Lib/test/test_posixpath.py b/Lib/test/test_posixpath.py
index cbb7c4c52d9697..807f985f7f4df7 100644
--- a/Lib/test/test_posixpath.py
+++ b/Lib/test/test_posixpath.py
@@ -456,6 +456,15 @@ def test_realpath_relative(self):
         finally:
             os_helper.unlink(ABSTFN)
 
+    @os_helper.skip_unless_symlink
+    @skip_if_ABSTFN_contains_backslash
+    def test_realpath_missing_pardir(self):
+        try:
+            os.symlink(os_helper.TESTFN + "1", os_helper.TESTFN)
+            self.assertEqual(realpath("nonexistent/../" + os_helper.TESTFN), ABSTFN + "1")
+        finally:
+            os_helper.unlink(os_helper.TESTFN)
+
     @os_helper.skip_unless_symlink
     @skip_if_ABSTFN_contains_backslash
     def test_realpath_symlink_loops(self):

From eed739a6d26fa71b05a6ecd50a1f65dbb1e05c06 Mon Sep 17 00:00:00 2001
From: Barney Gale <barney.gale@gmail.com>
Date: Fri, 5 Apr 2024 13:02:19 +0100
Subject: [PATCH 17/17] Update Lib/posixpath.py

Co-authored-by: Petr Viktorin <encukou@gmail.com>
---
 Lib/posixpath.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index ad895de3935b27..0e8bb5ab10d916 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -431,7 +431,8 @@ def realpath(filename, *, strict=False):
     seen = {}
 
     # Whether we're calling lstat() and readlink() to resolve symlinks. If we
-    # encounter an OSError in non-strict mode, this is switched off.
+    # encounter an OSError for a symlink loop in non-strict mode, this is
+    # switched off.
     querying = True
 
     while rest: