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reSTify PEP 355 (#324)

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Huang Huang 2017-08-17 06:39:21 +08:00 committed by Brett Cannon
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@ -5,18 +5,19 @@ Last-Modified: $Date$
Author: Björn Lindqvist <bjourne@gmail.com>
Status: Rejected
Type: Standards Track
Content-Type: text/plain
Content-Type: text/x-rst
Created: 24-Jan-2006
Python-Version: 2.5
Post-History:
Rejection Notice
================
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 open()? Or execfile()?)
implement **all** functionality that uses a path as a method on a single
class is an anti-pattern. (E.g. why not ``open()``? Or ``execfile()``?)
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,
@ -25,27 +26,29 @@ Rejection Notice
Abstract
========
This PEP describes a new class, Path, to be added to the os
This PEP describes a new class, ``Path``, to be added to the ``os``
module, for handling paths in an object oriented fashion. The
"weak" deprecation of various related functions is also discussed
and recommended.
Background
==========
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 [2]. In 2003,
module is inadequate. The first proposal for a ``Path`` object was
raised by Just van Rossum on python-dev in 2001 [2]_. In 2003,
Jason Orendorff released version 1.0 of the "path module" which
was the first public implementation that used objects to represent
paths [3].
paths [3]_.
The path module quickly became very popular and numerous attempts
were made to get the path module included in the Python standard
library; [4], [5], [6], [7].
library; [4]_, [5]_, [6]_, [7]_.
This PEP summarizes the ideas and suggestions people have
expressed about the path module and proposes that a modified
@ -53,6 +56,7 @@ Background
Motivation
==========
Dealing with filesystem paths is a common task in any programming
language, and very common in a high-level language like Python.
@ -70,13 +74,13 @@ Motivation
makes it hard for newbies and experienced developers to choose
the right method.
The Path class provides the following enhancements over the
The ``Path`` class provides the following enhancements over the
current common practice:
- One "unified" object provides all functionality from previous
functions.
- Subclassability - the Path object can be extended to support
- Subclassability - the ``Path`` object can be extended to support
paths other than filesystem paths. The programmer does not need
to learn a new API, but can reuse his or her knowledge of Path
to deal with the extended class.
@ -87,37 +91,38 @@ Motivation
- 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. Path objects is
merely strings to be passed to functions. ``Path`` objects is
inherently a pythonic idea.
- Path takes advantage of properties. Properties make for more
readable code.
- ``Path`` takes advantage of properties. Properties make for more
readable code::
if imgpath.ext == 'jpg':
jpegdecode(imgpath)
Is better than:
Is better than::
if os.path.splitexit(imgpath)[1] == 'jpg':
jpegdecode(imgpath)
Rationale
=========
The following points summarize the design:
- Path extends from string, therefore all code which expects
- ``Path`` extends from string, therefore all code which expects
string pathnames need not be modified and no existing code will
break.
- A Path object can be created either by using the classmethod
Path.cwd, by instantiating the class with a string representing
- A ``Path`` object 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 Path(".").
to ``Path(".")``.
- Path provides common pathname manipulation, pattern expansion,
- ``Path`` provides common pathname manipulation, pattern expansion,
pattern matching and other high-level file operations including
copying. Basically Path provides everything path-related except
copying. Basically ``Path`` provides everything path-related except
the manipulation of file contents, for which file objects are
better suited.
@ -126,10 +131,11 @@ Rationale
Specification
=============
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):
for brevity; see the reference implementation for more detail)::
class Path(str):
@ -161,7 +167,7 @@ Specification
"""p.splitpath() -> Return (p.parent, p.name)."""
def stripext(self) => Path
"""p.stripext() -> Remove one file extension from the path."""
def splitunc(self): ... [1]
def splitunc(self): ... [1]_
def splitall(self): ...
def relpath(self): ...
def relpathto(self, dest): ...
@ -213,7 +219,7 @@ Specification
def isfile(self): ...
def islink(self): ...
def ismount(self): ...
def samefile(self, other): ... [1]
def samefile(self, other): ... [1]_
def atime(self): ...
"""Last access time of the file."""
def mtime(self): ...
@ -225,17 +231,17 @@ Specification
Windows), is the creation time for path.
"""
def size(self): ...
def access(self, mode): ... [1]
def access(self, mode): ... [1]_
def stat(self): ...
def lstat(self): ...
def statvfs(self): ... [1]
def pathconf(self, name): ... [1]
def statvfs(self): ... [1]_
def pathconf(self, name): ... [1]_
# Methods for manipulating information about the filesystem
# path.
def utime(self, times) => None
def chmod(self, mode) => None
def chown(self, uid, gid) => None [1]
def chown(self, uid, gid) => None [1]_
def rename(self, new) => None
def renames(self, new) => None
@ -267,20 +273,20 @@ Specification
def rmtree(self, ignore_errors = False, onerror = None): ...
# Special stuff from os
def chroot(self): ... [1]
def startfile(self): ... [1]
def chroot(self): ... [1]_
def startfile(self): ... [1]_
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
imported with "from path import Path".
In the following examples, we assume that the ``Path`` class is
imported with ``from path import Path``.
1. Replacing os.path.join
--------------------------
* Replacing ``os.path.join``::
os.path.join(os.getcwd(), "foobar")
==>
@ -291,8 +297,7 @@ Replacing older functions with the Path class
Path("foo", "bar", "baz")
2. Replacing os.path.splitext
------------------------------
* Replacing ``os.path.splitext``::
fname = "Python2.4.tar.gz"
os.path.splitext(fname)[1]
@ -300,7 +305,7 @@ Replacing older functions with the Path class
fname = Path("Python2.4.tar.gz")
fname.ext
Or if you want both parts:
Or if you want both parts::
fname = "Python2.4.tar.gz"
base, ext = os.path.splitext(fname)
@ -309,8 +314,7 @@ Replacing older functions with the Path class
base, ext = fname.namebase, fname.extx
3. Replacing glob.glob
-----------------------
* Replacing ``glob.glob``::
lib_dir = "/lib"
libs = glob.glob(os.path.join(lib_dir, "*s.o"))
@ -320,6 +324,7 @@ Replacing older functions with the Path class
Deprecations
============
Introducing this module to the standard library introduces a need
for the "weak" deprecation of a number of existing modules and
@ -331,8 +336,9 @@ Deprecations
The table below lists the existing functionality that should be
deprecated.
==================== ===============================
Path method/property Deprecates function
-------------------- -------------------
==================== ===============================
normcase() os.path.normcase()
normpath() os.path.normpath()
realpath() os.path.realpath()
@ -390,32 +396,34 @@ Deprecations
copytree() shutil.copytree()
move() shutil.move()
rmtree() shutil.rmtree()
==================== ===============================
The Path class deprecates the whole of os.path, shutil, fnmatch
and glob. A big chunk of os is also deprecated.
The ``Path`` class deprecates the whole of ``os.path``, ``shutil``, ``fnmatch``
and ``glob``. A big chunk of ``os`` is also deprecated.
Closed Issues
=============
A number contentious issues have been resolved since this PEP
first appeared on python-dev:
* The __div__() method was removed. Overloading the / (division)
* The ``__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, __new__() got an *args
argument that accepts both Path and string objects. The *args
are concatenated with os.path.join() which is used to construct
the Path object. These changes obsoleted the problematic
joinpath() method which was removed.
if the BDFL so desires. In its place, ``__new__()`` got an ``*args``
argument that accepts both ``Path`` and string objects. The ``*args``
are concatenated with ``os.path.join()`` which is used to construct
the ``Path`` object. These changes obsoleted the problematic
``joinpath()`` method which was removed.
* The methods and the properties getatime()/atime,
getctime()/ctime, getmtime()/mtime and getsize()/size duplicated
* The methods and the properties ``getatime()/atime``,
``getctime()/ctime``, ``getmtime()/mtime`` and ``getsize()/size`` duplicated
each other. These methods and properties have been merged to
atime(), ctime(), mtime() and size(). The reason they are not
``atime()``, ``ctime()``, ``mtime()`` and ``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:
guaranteed to always pass the assertion::
p = Path("foobar")
s = p.size()
@ -423,27 +431,28 @@ Closed Issues
Open Issues
===========
Some functionality of Jason Orendorff's path module have been
omitted:
* Function for opening a path - better handled by the builtin
open().
``open()``.
* Functions for reading and writing whole files - better handled
by file objects' own read() and write() methods.
by file objects' own ``read()`` and ``write()`` methods.
* A chdir() function may be a worthy inclusion.
* A ``chdir()`` function may be a worthy inclusion.
* A deprecation schedule needs to be set up. How much
functionality should Path implement? How much of existing
functionality should ``Path`` implement? 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 os?
should it live? In its own module or in ``os``?
* Due to Path subclassing either str or unicode, the following
non-magic, public methods are available on Path objects:
* Due to ``Path`` subclassing either ``str`` or ``unicode``, the following
non-magic, public methods are available on ``Path`` objects::
capitalize(), center(), count(), decode(), encode(),
endswith(), expandtabs(), find(), index(), isalnum(),
@ -458,28 +467,29 @@ Open Issues
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 Path objects without
because it allows code to "just work" with ``Path`` objects 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 str or
unicode. Therefore, to not inherit from string requires changes
to the builtin function ``open()`` (and other builtins expecting a
string or buffer), unless the object inherits from either ``str`` or
``unicode``. Therefore, to not inherit from string requires changes
in CPython's core.
The functions and modules that this new module is trying to
replace (os.path, shutil, fnmatch, glob and parts of os) are
replace (``os.path``, ``shutil``, ``fnmatch``, ``glob`` and parts of ``os``) are
expected to be available in future Python versions for a long
time, to preserve backwards compatibility.
Reference Implementation
========================
Currently, the Path class is implemented as a thin wrapper around
the standard library modules fnmatch, glob, os, os.path and
shutil. The intention of this PEP is to move functionality from
the aforementioned modules to Path while they are being
Currently, the ``Path`` class is implemented as a thin wrapper around
the standard library modules ``fnmatch``, ``glob``, ``os``, ``os.path`` and
``shutil``. The intention of this PEP is to move functionality from
the aforementioned modules to ``Path`` while they are being
deprecated.
For more detail and an implementation see:
@ -488,12 +498,12 @@ Reference Implementation
Examples
========
In this section, "a ==> b" means that b can be used as a
replacement for a.
1. Make all python files in the a directory executable
------------------------------------------------------
* Make all python files in the a directory executable::
DIR = '/usr/home/guido/bin'
for f in os.listdir(DIR):
@ -504,8 +514,7 @@ Examples
for f in Path('/usr/home/guido/bin').files("*.py"):
f.chmod(0755)
2. Delete emacs backup files
----------------------------
* Delete emacs backup files::
def delete_backups(arg, dirname, names):
for name in names:
@ -517,53 +526,52 @@ Examples
for f in d.walkfiles('*~'):
f.remove()
3. Finding the relative path to a file
--------------------------------------
* Finding the relative path to a file::
b = Path('/users/peter/')
a = Path('/users/peter/synergy/tiki.txt')
a.relpathto(b)
4. Splitting a path into directory and filename
-----------------------------------------------
* Splitting a path into directory and filename::
os.path.split("/path/to/foo/bar.txt")
==>
Path("/path/to/foo/bar.txt").splitpath()
5. List all Python scripts in the current directory tree
--------------------------------------------------------
* List all Python scripts in the current directory tree::
list(Path().walkfiles("*.py"))
References and Footnotes
========================
[1] Method is not guaranteed to be available on all platforms.
.. [1] Method is not guaranteed to be available on all platforms.
[2] "(idea) subclassable string: path object?", van Rossum, 2001
.. [2] "(idea) subclassable string: path object?", van Rossum, 2001
https://mail.python.org/pipermail/python-dev/2001-August/016663.html
[3] "path module v1.0 released", Orendorff, 2003
.. [3] "path module v1.0 released", Orendorff, 2003
https://mail.python.org/pipermail/python-announce-list/2003-January/001984.html
[4] "Some RFE for review", Birkenfeld, 2005
.. [4] "Some RFE for review", Birkenfeld, 2005
https://mail.python.org/pipermail/python-dev/2005-June/054438.html
[5] "path module", Orendorff, 2003
.. [5] "path module", Orendorff, 2003
https://mail.python.org/pipermail/python-list/2003-July/174289.html
[6] "PRE-PEP: new Path class", Roth, 2004
.. [6] "PRE-PEP: new Path class", Roth, 2004
https://mail.python.org/pipermail/python-list/2004-January/201672.html
[7] http://wiki.python.org/moin/PathClass
.. [7] http://wiki.python.org/moin/PathClass
Copyright
=========
This document has been placed in the public domain.
..
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