PEP 355 – Path - Object oriented filesystem paths
- Björn Lindqvist <bjourne at gmail.com>
- Standards Track
This PEP has been rejected (in this form). The proposed path class
is the ultimate kitchen sink; but the notion that it’s better to
implement all functionality that uses a path as a method on a single
class is an anti-pattern. (E.g. why not
Subclassing from str is a particularly bad idea; many string
operations make no sense when applied to a path. This PEP has
lingered, and while the discussion flares up from time to time,
it’s time to put this PEP out of its misery. A less far-fetched
proposal might be more palatable.
This PEP describes a new class,
Path, to be added to the
module, for handling paths in an object oriented fashion. The
“weak” deprecation of various related functions is also discussed
The ideas expressed in this PEP are not recent, but have been
debated in the Python community for many years. Many have felt
that the API for manipulating file paths as offered in the os.path
module is inadequate. The first proposal for a
Path object was
raised by Just van Rossum on python-dev in 2001 . In 2003,
Jason Orendorff released version 1.0 of the “path module” which
was the first public implementation that used objects to represent
The path module quickly became very popular and numerous attempts were made to get the path module included in the Python standard library; , , , .
This PEP summarizes the ideas and suggestions people have expressed about the path module and proposes that a modified version should be included in the standard library.
Dealing with filesystem paths is a common task in any programming language, and very common in a high-level language like Python. Good support for this task is needed, because:
- Almost every program uses paths to access files. It makes sense that a task, that is so often performed, should be as intuitive and as easy to perform as possible.
- It makes Python an even better replacement language for over-complicated shell scripts.
Currently, Python has a large number of different functions scattered over half a dozen modules for handling paths. This makes it hard for newbies and experienced developers to choose the right method.
Path class provides the following enhancements over the
current common practice:
- One “unified” object provides all functionality from previous functions.
- Subclassability - the
Pathobject can be extended to support paths other than filesystem paths. The programmer does not need to learn a new API, but can reuse their knowledge of Path to deal with the extended class.
- With all related functionality in one place, the right approach is easier to learn as one does not have to hunt through many different modules for the right functions.
- Python is an object oriented language. Just like files,
datetimes and sockets are objects so are paths, they are not
merely strings to be passed to functions.
Pathobjects is inherently a pythonic idea.
Pathtakes advantage of properties. Properties make for more readable code:
if imgpath.ext == 'jpg': jpegdecode(imgpath)
Is better than:
if os.path.splitexit(imgpath) == 'jpg': jpegdecode(imgpath)
The following points summarize the design:
Pathextends from string, therefore all code which expects string pathnames need not be modified and no existing code will break.
Pathobject can be created either by using the classmethod
Path.cwd, by instantiating the class with a string representing a path or by using the default constructor which is equivalent to
Pathprovides common pathname manipulation, pattern expansion, pattern matching and other high-level file operations including copying. Basically
Pathprovides everything path-related except the manipulation of file contents, for which file objects are better suited.
- Platform incompatibilities are dealt with by not instantiating system specific methods.
This class defines the following public interface (docstrings have been extracted from the reference implementation, and shortened for brevity; see the reference implementation for more detail):
class Path(str): # Special Python methods: def __new__(cls, *args) => Path """ Creates a new path object concatenating the *args. *args may only contain Path objects or strings. If *args is empty, Path(os.curdir) is created. """ def __repr__(self): ... def __add__(self, more): ... def __radd__(self, other): ... # Alternative constructor. def cwd(cls): ... # Operations on path strings: def abspath(self) => Path """Returns the absolute path of self as a new Path object.""" def normcase(self): ... def normpath(self): ... def realpath(self): ... def expanduser(self): ... def expandvars(self): ... def basename(self): ... def expand(self): ... def splitpath(self) => (Path, str) """p.splitpath() -> Return (p.parent, p.name).""" def stripext(self) => Path """p.stripext() -> Remove one file extension from the path.""" def splitunc(self): ... _ def splitall(self): ... def relpath(self): ... def relpathto(self, dest): ... # Properties about the path: parent => Path """This Path's parent directory as a new path object.""" name => str """The name of this file or directory without the full path.""" ext => str """ The file extension or an empty string if Path refers to a file without an extension or a directory. """ drive => str """ The drive specifier. Always empty on systems that don't use drive specifiers. """ namebase => str """ The same as path.name, but with one file extension stripped off. """ uncshare # Operations that return lists of paths: def listdir(self, pattern = None): ... def dirs(self, pattern = None): ... def files(self, pattern = None): ... def walk(self, pattern = None): ... def walkdirs(self, pattern = None): ... def walkfiles(self, pattern = None): ... def match(self, pattern) => bool """Returns True if self.name matches the given pattern.""" def matchcase(self, pattern) => bool """ Like match() but is guaranteed to be case sensitive even on platforms with case insensitive filesystems. """ def glob(self, pattern): # Methods for retrieving information about the filesystem # path: def exists(self): ... def isabs(self): ... def isdir(self): ... def isfile(self): ... def islink(self): ... def ismount(self): ... def samefile(self, other): ... _ def atime(self): ... """Last access time of the file.""" def mtime(self): ... """Last-modified time of the file.""" def ctime(self): ... """ Return the system's ctime which, on some systems (like Unix) is the time of the last change, and, on others (like Windows), is the creation time for path. """ def size(self): ... def access(self, mode): ... _ def stat(self): ... def lstat(self): ... def statvfs(self): ... _ def pathconf(self, name): ... _ # Methods for manipulating information about the filesystem # path. def utime(self, times) => None def chmod(self, mode) => None def chown(self, uid, gid) => None _ def rename(self, new) => None def renames(self, new) => None # Create/delete operations on directories def mkdir(self, mode = 0777): ... def makedirs(self, mode = 0777): ... def rmdir(self): ... def removedirs(self): ... # Modifying operations on files def touch(self): ... def remove(self): ... def unlink(self): ... # Modifying operations on links def link(self, newpath): ... def symlink(self, newlink): ... def readlink(self): ... def readlinkabs(self): ... # High-level functions from shutil def copyfile(self, dst): ... def copymode(self, dst): ... def copystat(self, dst): ... def copy(self, dst): ... def copy2(self, dst): ... def copytree(self, dst, symlinks = True): ... def move(self, dst): ... def rmtree(self, ignore_errors = False, onerror = None): ... # Special stuff from os def chroot(self): ... _ def startfile(self): ... _
Replacing older functions with the Path class
In this section, “a ==> b” means that b can be used as a replacement for a.
In the following examples, we assume that the
Path class is
from path import Path.
os.path.join(os.getcwd(), "foobar") ==> Path(Path.cwd(), "foobar") os.path.join("foo", "bar", "baz") ==> Path("foo", "bar", "baz")
fname = "Python2.4.tar.gz" os.path.splitext(fname) ==> fname = Path("Python2.4.tar.gz") fname.ext
Or if you want both parts:
fname = "Python2.4.tar.gz" base, ext = os.path.splitext(fname) ==> fname = Path("Python2.4.tar.gz") base, ext = fname.namebase, fname.extx
lib_dir = "/lib" libs = glob.glob(os.path.join(lib_dir, "*s.o")) ==> lib_dir = Path("/lib") libs = lib_dir.files("*.so")
Introducing this module to the standard library introduces a need for the “weak” deprecation of a number of existing modules and functions. These modules and functions are so widely used that they cannot be truly deprecated, as in generating DeprecationWarning. Here “weak deprecation” means notes in the documentation only.
The table below lists the existing functionality that should be deprecated.
|Path method/property||Deprecates function|
Path class deprecates the whole of
glob. A big chunk of
os is also deprecated.
A number contentious issues have been resolved since this PEP first appeared on python-dev:
__div__()method was removed. Overloading the / (division) operator may be “too much magic” and make path concatenation appear to be division. The method can always be re-added later if the BDFL so desires. In its place,
*argsargument that accepts both
Pathand string objects. The
*argsare concatenated with
os.path.join()which is used to construct the
Pathobject. These changes obsoleted the problematic
joinpath()method which was removed.
- The methods and the properties
getsize()/sizeduplicated each other. These methods and properties have been merged to
size(). The reason they are not properties instead, is because there is a possibility that they may change unexpectedly. The following example is not guaranteed to always pass the assertion:
p = Path("foobar") s = p.size() assert p.size() == s
Some functionality of Jason Orendorff’s path module have been omitted:
- Function for opening a path - better handled by the builtin
- Functions for reading and writing whole files - better handled
by file objects’ own
chdir()function may be a worthy inclusion.
- A deprecation schedule needs to be set up. How much
Pathimplement? How much of existing functionality should it deprecate and when?
- The name obviously has to be either “path” or “Path,” but where
should it live? In its own module or in
- Due to
unicode, the following non-magic, public methods are available on
capitalize(), center(), count(), decode(), encode(), endswith(), expandtabs(), find(), index(), isalnum(), isalpha(), isdigit(), islower(), isspace(), istitle(), isupper(), join(), ljust(), lower(), lstrip(), replace(), rfind(), rindex(), rjust(), rsplit(), rstrip(), split(), splitlines(), startswith(), strip(), swapcase(), title(), translate(), upper(), zfill()
On python-dev it has been argued whether this inheritance is sane or not. Most persons debating said that most string methods doesn’t make sense in the context of filesystem paths – they are just dead weight. The other position, also argued on python-dev, is that inheriting from string is very convenient because it allows code to “just work” with
Pathobjects without having to be adapted for them.
One of the problems is that at the Python level, there is no way to make an object “string-like enough,” so that it can be passed to the builtin function
open()(and other builtins expecting a string or buffer), unless the object inherits from either
unicode. Therefore, to not inherit from string requires changes in CPython’s core.
The functions and modules that this new module is trying to
glob and parts of
expected to be available in future Python versions for a long
time, to preserve backwards compatibility.
Path class is implemented as a thin wrapper around
the standard library modules
shutil. The intention of this PEP is to move functionality from
the aforementioned modules to
Path while they are being
For more detail and an implementation see:
In this section, “a ==> b” means that b can be used as a replacement for a.
- Make all python files in the a directory executable:
DIR = '/usr/home/guido/bin' for f in os.listdir(DIR): if f.endswith('.py'): path = os.path.join(DIR, f) os.chmod(path, 0755) ==> for f in Path('/usr/home/guido/bin').files("*.py"): f.chmod(0755)
- Delete emacs backup files:
def delete_backups(arg, dirname, names): for name in names: if name.endswith('~'): os.remove(os.path.join(dirname, name)) os.path.walk(os.environ['HOME'], delete_backups, None) ==> d = Path(os.environ['HOME']) for f in d.walkfiles('*~'): f.remove()
- Finding the relative path to a file:
b = Path('/users/peter/') a = Path('/users/peter/synergy/tiki.txt') a.relpathto(b)
- Splitting a path into directory and filename:
os.path.split("/path/to/foo/bar.txt") ==> Path("/path/to/foo/bar.txt").splitpath()
- List all Python scripts in the current directory tree:
References and Footnotes
- Method is not guaranteed to be available on all platforms.
- “(idea) subclassable string: path object?”, van Rossum, 2001 https://mail.python.org/pipermail/python-dev/2001-August/016663.html
- “path module v1.0 released”, Orendorff, 2003 https://mail.python.org/pipermail/python-announce-list/2003-January/001984.html
- “Some RFE for review”, Birkenfeld, 2005 https://mail.python.org/pipermail/python-dev/2005-June/054438.html
- “path module”, Orendorff, 2003 https://mail.python.org/pipermail/python-list/2003-July/174289.html
- “PRE-PEP: new Path class”, Roth, 2004 https://mail.python.org/pipermail/python-list/2004-January/201672.html
This document has been placed in the public domain.
Last modified: 2022-01-21 21:08:11 GMT