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|
scandir, a better directory iterator and faster os.walk()
=========================================================
.. image:: https://img.shields.io/pypi/v/scandir.svg
:target: https://pypi.python.org/pypi/scandir
:alt: scandir on PyPI (Python Package Index)
.. image:: https://travis-ci.org/benhoyt/scandir.svg?branch=master
:target: https://travis-ci.org/benhoyt/scandir
:alt: Travis CI tests (Linux)
.. image:: https://ci.appveyor.com/api/projects/status/github/benhoyt/scandir?branch=master&svg=true
:target: https://ci.appveyor.com/project/benhoyt/scandir
:alt: Appveyor tests (Windows)
``scandir()`` is a directory iteration function like ``os.listdir()``,
except that instead of returning a list of bare filenames, it yields
``DirEntry`` objects that include file type and stat information along
with the name. Using ``scandir()`` increases the speed of ``os.walk()``
by 2-20 times (depending on the platform and file system) by avoiding
unnecessary calls to ``os.stat()`` in most cases.
Now included in a Python near you!
----------------------------------
``scandir`` has been included in the Python 3.5 standard library as
``os.scandir()``, and the related performance improvements to
``os.walk()`` have also been included. So if you're lucky enough to be
using Python 3.5 (release date September 13, 2015) you get the benefit
immediately, otherwise just
`download this module from PyPI <https://pypi.python.org/pypi/scandir>`_,
install it with ``pip install scandir``, and then do something like
this in your code:
.. code-block:: python
# Use the built-in version of scandir/walk if possible, otherwise
# use the scandir module version
try:
from os import scandir, walk
except ImportError:
from scandir import scandir, walk
`PEP 471 <https://www.python.org/dev/peps/pep-0471/>`_, which is the
PEP that proposes including ``scandir`` in the Python standard library,
was `accepted <https://mail.python.org/pipermail/python-dev/2014-July/135561.html>`_
in July 2014 by Victor Stinner, the BDFL-delegate for the PEP.
This ``scandir`` module is intended to work on Python 2.7+ and Python
3.4+ (and it has been tested on those versions).
Background
----------
Python's built-in ``os.walk()`` is significantly slower than it needs to be,
because -- in addition to calling ``listdir()`` on each directory -- it calls
``stat()`` on each file to determine whether the filename is a directory or not.
But both ``FindFirstFile`` / ``FindNextFile`` on Windows and ``readdir`` on Linux/OS
X already tell you whether the files returned are directories or not, so
no further ``stat`` system calls are needed. In short, you can reduce the number
of system calls from about 2N to N, where N is the total number of files and
directories in the tree.
In practice, removing all those extra system calls makes ``os.walk()`` about
**7-50 times as fast on Windows, and about 3-10 times as fast on Linux and Mac OS
X.** So we're not talking about micro-optimizations. See more benchmarks
in the "Benchmarks" section below.
Somewhat relatedly, many people have also asked for a version of
``os.listdir()`` that yields filenames as it iterates instead of returning them
as one big list. This improves memory efficiency for iterating very large
directories.
So as well as a faster ``walk()``, scandir adds a new ``scandir()`` function.
They're pretty easy to use, but see "The API" below for the full docs.
Benchmarks
----------
Below are results showing how many times as fast ``scandir.walk()`` is than
``os.walk()`` on various systems, found by running ``benchmark.py`` with no
arguments:
==================== ============== =============
System version Python version Times as fast
==================== ============== =============
Windows 7 64-bit 2.7.7 64-bit 10.4
Windows 7 64-bit SSD 2.7.7 64-bit 10.3
Windows 7 64-bit NFS 2.7.6 64-bit 36.8
Windows 7 64-bit SSD 3.4.1 64-bit 9.9
Windows 7 64-bit SSD 3.5.0 64-bit 9.5
Ubuntu 14.04 64-bit 2.7.6 64-bit 5.8
Mac OS X 10.9.3 2.7.5 64-bit 3.8
==================== ============== =============
All of the above tests were done using the fast C version of scandir
(source code in ``_scandir.c``).
Note that the gains are less than the above on smaller directories and greater
on larger directories. This is why ``benchmark.py`` creates a test directory
tree with a standardized size.
The API
-------
walk()
~~~~~~
The API for ``scandir.walk()`` is exactly the same as ``os.walk()``, so just
`read the Python docs <https://docs.python.org/3.5/library/os.html#os.walk>`_.
scandir()
~~~~~~~~~
The full docs for ``scandir()`` and the ``DirEntry`` objects it yields are
available in the `Python documentation here <https://docs.python.org/3.5/library/os.html#os.scandir>`_.
But below is a brief summary as well.
scandir(path='.') -> iterator of DirEntry objects for given path
Like ``listdir``, ``scandir`` calls the operating system's directory
iteration system calls to get the names of the files in the given
``path``, but it's different from ``listdir`` in two ways:
* Instead of returning bare filename strings, it returns lightweight
``DirEntry`` objects that hold the filename string and provide
simple methods that allow access to the additional data the
operating system may have returned.
* It returns a generator instead of a list, so that ``scandir`` acts
as a true iterator instead of returning the full list immediately.
``scandir()`` yields a ``DirEntry`` object for each file and
sub-directory in ``path``. Just like ``listdir``, the ``'.'``
and ``'..'`` pseudo-directories are skipped, and the entries are
yielded in system-dependent order. Each ``DirEntry`` object has the
following attributes and methods:
* ``name``: the entry's filename, relative to the scandir ``path``
argument (corresponds to the return values of ``os.listdir``)
* ``path``: the entry's full path name (not necessarily an absolute
path) -- the equivalent of ``os.path.join(scandir_path, entry.name)``
* ``is_dir(*, follow_symlinks=True)``: similar to
``pathlib.Path.is_dir()``, but the return value is cached on the
``DirEntry`` object; doesn't require a system call in most cases;
don't follow symbolic links if ``follow_symlinks`` is False
* ``is_file(*, follow_symlinks=True)``: similar to
``pathlib.Path.is_file()``, but the return value is cached on the
``DirEntry`` object; doesn't require a system call in most cases;
don't follow symbolic links if ``follow_symlinks`` is False
* ``is_symlink()``: similar to ``pathlib.Path.is_symlink()``, but the
return value is cached on the ``DirEntry`` object; doesn't require a
system call in most cases
* ``stat(*, follow_symlinks=True)``: like ``os.stat()``, but the
return value is cached on the ``DirEntry`` object; does not require a
system call on Windows (except for symlinks); don't follow symbolic links
(like ``os.lstat()``) if ``follow_symlinks`` is False
* ``inode()``: return the inode number of the entry; the return value
is cached on the ``DirEntry`` object
Here's a very simple example of ``scandir()`` showing use of the
``DirEntry.name`` attribute and the ``DirEntry.is_dir()`` method:
.. code-block:: python
def subdirs(path):
"""Yield directory names not starting with '.' under given path."""
for entry in os.scandir(path):
if not entry.name.startswith('.') and entry.is_dir():
yield entry.name
This ``subdirs()`` function will be significantly faster with scandir
than ``os.listdir()`` and ``os.path.isdir()`` on both Windows and POSIX
systems, especially on medium-sized or large directories.
Further reading
---------------
* `The Python docs for scandir <https://docs.python.org/3.5/library/os.html#os.scandir>`_
* `PEP 471 <https://www.python.org/dev/peps/pep-0471/>`_, the
(now-accepted) Python Enhancement Proposal that proposed adding
``scandir`` to the standard library -- a lot of details here,
including rejected ideas and previous discussion
Flames, comments, bug reports
-----------------------------
Please send flames, comments, and questions about scandir to Ben Hoyt:
http://benhoyt.com/
File bug reports for the version in the Python 3.5 standard library
`here <https://docs.python.org/3.5/bugs.html>`_, or file bug reports
or feature requests for this module at the GitHub project page:
https://github.com/benhoyt/scandir
|
