gh-117349: Micro-optimize a few os.path functions

Lib/ntpath.py

@@ -102,11 +102,11 @@ def join(path, *paths):
  if isinstance(path, bytes):
  sep = b'\\'
  seps = b'\\/'
-colon = b':'
+colon_seps = b':\\/'
  else:
  sep = '\\'
  seps = '\\/'
-colon = ':'
+colon_seps = ':\\/'
  try:
  if not paths:
  path[:0] + sep #23780: Ensure compatible data type even if p is null.
@@ -135,7 +135,7 @@ def join(path, *paths):
  result_path = result_path + p_path
  ## add separator between UNC and non-absolute path
  if (result_path and not result_root and
- result_drive and result_drive[-1:] not in colon + seps):
+ result_drive and result_drive[-1] not in colon_seps):
  return result_drive + sep + result_path
  return result_drive + result_root + result_path
  except (TypeError, AttributeError, BytesWarning):
@@ -279,7 +279,7 @@ def isjunction(path):
  st = os.lstat(path)
  except (OSError, ValueError, AttributeError):
  return False
- return bool(st.st_reparse_tag == stat.IO_REPARSE_TAG_MOUNT_POINT)
+ return st.st_reparse_tag == stat.IO_REPARSE_TAG_MOUNT_POINT
 else:
  # Use genericpath.isjunction as imported above
  pass
@@ -340,8 +340,8 @@ def isreserved(path):
 def _isreservedname(name):
  """Return true if the filename is reserved by the system."""
  # Trailing dots and spaces are reserved.
- if name.endswith(('.', ' ')) and name not in ('.', '..'):
- return True
+ if name[-1:] in ('.', ''):
+ return name not in ('.', '..')
  # Wildcards, separators, colon, and pipe (*?"<>/\:|) are reserved.
  # ASCII control characters (0-31) are reserved.
  # Colon is reserved for file streams (e.g. "name:stream[:type]").
@@ -350,9 +350,7 @@ def _isreservedname(name):
  # DOS device names are reserved (e.g. "nul" or "nul .txt"). The rules
  # are complex and vary across Windows versions. On the side of
  # caution, return True for names that may not be reserved.
- if name.partition('.')[0].rstrip(' ').upper() in _reserved_names:
- return True
- return False
+ return name.partition('.')[0].rstrip(' ').upper() in _reserved_names
 
 
 # Expand paths beginning with '~' or '~user'.
@@ -381,13 +379,10 @@ def expanduser(path):
 
  if 'USERPROFILE' in os.environ:
  userhome = os.environ['USERPROFILE']
- elif not 'HOMEPATH' in os.environ:
+ elif 'HOMEPATH' not in os.environ:
  return path
  else:
- try:
- drive = os.environ['HOMEDRIVE']
- except KeyError:
- drive = ''
+ drive = os.environ.get('HOMEDRIVE', '')
  userhome = join(drive, os.environ['HOMEPATH'])
 
  if i != 1: #~user
@@ -727,15 +722,17 @@ def realpath(path, *, strict=False):
  new_unc_prefix = b'\\\\'
  cwd = os.getcwdb()
  # bpo-38081: Special case for realpath(b'nul')
- if normcase(path) == normcase(os.fsencode(devnull)):
+ devnull = b'nul'
+ if normcase(path) == devnull:
  return b'\\\\.\\NUL'
  else:
  prefix = '\\\\?\\'
  unc_prefix = '\\\\?\\UNC\\'
  new_unc_prefix = '\\\\'
  cwd = os.getcwd()
  # bpo-38081: Special case for realpath('nul')
- if normcase(path) == normcase(devnull):
+ devnull = 'nul'
+ if normcase(path) == devnull:
  return '\\\\.\\NUL'
  had_prefix = path.startswith(prefix)
  if not had_prefix and not isabs(path):

Lib/posixpath.py

@@ -213,15 +213,8 @@ def ismount(path):
  except (OSError, ValueError):
  return False
 
- dev1 = s1.st_dev
- dev2 = s2.st_dev
- if dev1 != dev2:
- return True # path/.. on a different device as path
- ino1 = s1.st_ino
- ino2 = s2.st_ino
- if ino1 == ino2:
- return True # path/.. is the same i-node as path
- return False
+ # path/.. on a different device as path or the same i-node as path
+ return s1.st_dev != s2.st_dev or s1.st_ino == s2.st_ino
 
 
 # Expand paths beginning with '~' or '~user'.
@@ -270,7 +263,7 @@ def expanduser(path):
  return path
  name = path[1:i]
  if isinstance(name, bytes):
- name = str(name, 'ASCII')
+ name = name.decode('ascii')
  try:
  pwent = pwd.getpwnam(name)
  except KeyError:
@@ -359,21 +352,19 @@ def normpath(path):
  path = os.fspath(path)
  if isinstance(path, bytes):
  sep = b'/'
- empty = b''
  dot = b'.'
  dotdot = b'..'
  else:
  sep = '/'
- empty = ''
  dot = '.'
  dotdot = '..'
- if path == empty:
+ if not path:
  return dot
  _, initial_slashes, path = splitroot(path)
  comps = path.split(sep)
  new_comps = []
  for comp in comps:
- if comp in (empty, dot):
+ if not comp or comp == dot:
  continue
  if (comp != dotdot or (not initial_slashes and not new_comps) or
  (new_comps and new_comps[-1] == dotdot)):
@@ -396,12 +387,12 @@ def normpath(path):
 def abspath(path):
  """Return an absolute path."""
  path = os.fspath(path)
- if not isabs(path):
- if isinstance(path, bytes):
-cwd = os.getcwdb()
-else:
- cwd = os.getcwd()
- path = join(cwd, path)
+ if isinstance(path, bytes):
+ if not path.startswith(b'/'):
+path = join(os.getcwdb(), path)
+ else:
+if not path.startswith('/'):
+path = join(os.getcwd(), path)
  return normpath(path)
 
 
@@ -417,6 +408,7 @@ def realpath(filename, *, strict=False):
 
 # Join two paths, normalizing and eliminating any symbolic links
 # encountered in the second path.
+# Two leading slashes are replaced by a single slash.
 def _joinrealpath(path, rest, strict, seen):
  if isinstance(path, bytes):
  sep = b'/'
@@ -427,7 +419,7 @@ def _joinrealpath(path, rest, strict, seen):
  curdir = '.'
  pardir = '..'
 
- if isabs(rest):
+ if rest.startswith(sep):
  rest = rest[1:]
  path = sep
 
@@ -439,10 +431,15 @@ def _joinrealpath(path, rest, strict, seen):
  if name == pardir:
  # parent dir
  if path:
-path, name = split(path)
+parent, name = split(path)
  if name == pardir:
- path = join(path, pardir, pardir)
+ # ../..
+ path = join(path, pardir)
+ else:
+ # foo/bar/.. -> foo
+ path = parent
  else:
+ # ..
  path = pardir
  continue
  newpath = join(path, name)

Misc/ACKS

@@ -191,6 +191,7 @@ Finn Bock
 Paul Boddie
 Matthew Boedicker
 Robin Boerdijk
+Wannes Boeykens
 Andra Bogildea
 Matt Bogosian
 Nikolay Bogoychev

Misc/NEWS.d/next/Core and Builtins/2024-03-29-15-04-13.gh-issue-117349.OB9kQQ.rst

@@ -0,0 +1 @@
+Optimise several functions in :mod:`os.path`.