benhoyt/ scandir

(v1.10.0) almost 2 years ago

Python

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benhoyt

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BSD 3-Clause "New" or "Revised" License

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Description

Better directory iterator and faster os.walk(), now in the Python 3.5 stdlib

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scandir, a better directory iterator and faster os.walk()

Name: scandir
Brand: scandir
SKU: //benhoyt/scandir
Rating: 2.9175 (467 reviews)

.. 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

_, 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

, which is the PEP that proposes including
scandir
in the Python standard library, was
accepted
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

scandir() ~~~~~~~~~

The full docs for

scandir()

and the

DirEntry

objects it yields are available in the

Python documentation here

_. But below is a brief summary as well.

scandir(path='.') -> iterator of DirEntry objects for given path

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.

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

_, or file bug reports or feature requests for this module at the GitHub project page:

https://github.com/benhoyt/scandir