Blog posts for tags/python

  1. psutil 3.0, aka how I reimplemented ifconfig in Python

    Here we are. It's been a long time since my last blog post and my last psutil release. The reason? I've been travelling! I mean... a lot. I've spent 3 months in Berlin, 3 weeks in Japan and 2 months in New York City. While I was there I finally had the chance to meet my friend Jay Loden in person. Jay and I originally started working on psutil together 7 years ago.

    Back then I didn't know any C (and I still am a terrible C developer) so he's been crucial to develop the initial psutil skeleton including OSX and Windows support. I'm back home now (but not for long ;-)), so I finally have some time to write this blog post and tell you about the new psutil release. Let's see what happened.

    net_if_addrs()

    In a few words, we're now able to list network interface addresses similarly to "ifconfig" command on UNIX:

    >>> import psutil
>>> from pprint import pprint
>>> pprint(psutil.net_if_addrs())
{'ethernet0': [snic(family=<AddressFamily.AF_INET: 2>,
                    address='10.0.0.4',
                    netmask='255.0.0.0',
                    broadcast='10.255.255.255'),
               snic(family=<AddressFamily.AF_PACKET: 17>,
                    address='9c:eb:e8:0b:05:1f',
                    netmask=None,
                    broadcast='ff:ff:ff:ff:ff:ff')],
 'localhost': [snic(family=<AddressFamily.AF_INET: 2>,
                    address='127.0.0.1',
                    netmask='255.0.0.0',
                    broadcast='127.0.0.1'),
               snic(family=<AddressFamily.AF_PACKET: 17>,
                    address='00:00:00:00:00:00',
                    netmask=None,
                    broadcast='00:00:00:00:00:00')]}

    This is limited to AF_INET (IPv4), AF_INET6 (IPv6) and AF_LINK (Ethernet) address families. If you want something more poweful (e.g. AF_BLUETOOTH) you can take a look at netifaces extension. And here's the code which does these tricks on POSIX and Windows:

    Also, here's some doc.

    net_if_stats()

    This will return a bunch of information about network interface cards:

    >>> import psutil
>>> from pprint import pprint
>>> pprint(psutil.net_if_stats())
{'ethernet'0: snicstats(isup=True,
                        duplex=<NicDuplex.NIC_DUPLEX_FULL: 2>,
                        speed=100,
                        mtu=1500),
 'localhost': snicstats(isup=True,
                        duplex=<NicDuplex.NIC_DUPLEX_UNKNOWN: 0>,
                        speed=0,
                        mtu=65536)}

    Again, here's the code for each platform:

    ...and the doc.

    Enums

    Enums are a nice new feature introduced in Python 3.4. Very briefly (or at least, this is what I appreciate the most about them), they help you write an API with human-readable constants. If you use Python 2 you'll see something like this:

    >>> import psutil
>>> psutil.IOPRIO_CLASS_IDLE
3

    On Python 3.4 you'll see a more informative:

    >>> import psutil
>>> psutil.IOPRIO_CLASS_IDLE
<IOPriority.IOPRIO_CLASS_IDLE: 3>

    They are backward compatible, meaning if you're sending serialized data produced with psutil through the network you can safely use comparison operators and so on. The psutil APIs returning enums (on Python >=3.4) are:

    • psutil.net_connections() (the address families):
    • psutil.Process.connections() (same as above)
    • psutil.net_if_stats() (all NIC_DUPLEX_* constants)
    • psutil.Process.nice() on Windows (for all the *_PRIORITY_CLASS constants)
    • psutil.Process.ionice() on Linux (for all the IOPRIO_CLASS_* constants)

    All the other existing constants remained plain strings (STATUS_*) or integers (CONN_*).

    Zombie processes

    This is a big one. The full story is here but basically the support for zombie processes on UNIX was broken (except on Linux, and Windows doesn't have zombie processes). Up until psutil 2.X we could instantiate a zombie process:

    >>> pid = create_zombie()
>>> p = psutil.Process(pid)

    ...but every time we queried it we got a NoSuchProcess exception:

    >>> psutil.name()
  File "psutil/__init__.py", line 374, in _init
    raise NoSuchProcess(pid, None, msg)
psutil.NoSuchProcess: no process found with pid 123

    That was misleading though because the PID technically still existed:

    >>> psutil.pid_exists(p.pid)
True

    Furthermore, depending on what platform you were on, certain process stats could still be queried (instead of raising NoSuchProcess):

    >>> psutil.cmdline()
['python']

    Also process_iter() did not return zombie processes at all. This was probably the worst aspect because being able to identify them is an important use case, as they signal an issue with process: if a parent process spawns a child, terminates it (via kill()), but doesn't wait() for it it will create a zombie. Long story short, the way this changed in psutil 3.0 is that:

    • we now have a new ZombieProcess exception, raised every time we're not able to query a process because it's a zombie
    • it is raised instead of NoSuchProcess (which was incorrect and misleading)
    • it is still backward compatible (meaning you won't have to change your old code) because it inherits from NoSuchProcess
    • process_iter() finally works, meaning you can safely identify zombie processes like this:
    import psutil
zombies = []
for p in psutil.process_iter():
    try:
        if p.status() == psutil.STATUS_ZOMBIE:
            zombies.append(p)
    except NoSuchProcess:
        pass

    Removal of deprecated APIs

    This is another big one, probably the biggest. In a previous blog post I already talked about deprecated APIs. What I did back then (January 2014) was to rename and officially deprecate different APIs and provide aliases for them so that people wouldn't yell at me because I broke their existent code. The most interesting deprecation was certainly the one affecting module constants and the hack which was used in order to provide "module properties". With this new release I decided to get rid of all those aliases. I'm sure this will cause problems but hey! This is a new major release, right? =). Plus the amount of crap which was removed is impressive (see the commit). Here's the old aliases which are now gone for good (or bad, depending on how much headache they will cause you):

    Removed module functions and constants

    Already deprecated name New name
    psutil.BOOT_TIME() psutil.boot_time()
    psutil.NUM_CPUS() psutil.cpu_count()
    psutil.TOTAL_PHYMEM() psutil.virtual_memory().total
    psutil.avail_phymem() psutil.virtual_memory().free
    psutil.avail_virtmem() psutil.swap_memory().free
    psutil.cached_phymem() psutil.virtual_memory().cached
    psutil.get_pid_list() psutil.pids().cached
    psutil.get_process_list()  
    psutil.get_users() psutil.users()
    psutil.network_io_counters() psutil.net_io_counters()
    psutil.phymem_buffers() psutil.virtual_memory().buffers
    psutil.phymem_usage() psutil.virtual_memory()
    psutil.total_virtmem() psutil.swap_memory().total
    psutil.used_virtmem() psutil.swap_memory().used
    psutil.used_phymem() psutil.virtual_memory().used
    psutil.virtmem_usage() psutil.swap_memory()

    Process methods (assuming p = psutil.Process()):

    Already deprecated name New name
    p.get_children() p.children()
    p.get_connections() p.connections()
    p.get_cpu_affinity() p.cpu_affinity()
    p.get_cpu_percent() p.cpu_percent()
    p.get_cpu_times() p.cpu_times()
    p.get_io_counters() p.io_counters()
    p.get_ionice() p.ionice()
    p.get_memory_info() p.memory_info()
    p.get_ext_memory_info() p.memory_info_ex()
    p.get_memory_maps() p.memory_maps()
    p.get_memory_percent() p.memory_percent()
    p.get_nice() p.nice()
    p.get_num_ctx_switches() p.num_ctx_switches()
    p.get_num_fds() p.num_fds()
    p.get_num_threads() p.num_threads()
    p.get_open_files() p.open_files()
    p.get_rlimit() p.rlimit()
    p.get_threads() p.threads()
    p.getcwd() p.cwd()
    p.set_cpu_affinity() p.cpu_affinity()
    p.set_ionice() p.ionice()
    p.set_nice() p.nice()
    p.set_rlimit() p.rlimit()

    If your code suddenly breaks with AttributeError after you upgraded psutil it means you were using one of those deprecated aliases. In that case just take a look at the table above and rename stuff in accordance.

    Bug fixes

    I fixed a lot of stuff (full list here), but here's the list of things which I think are worth mentioning:

    • #512: [FreeBSD] fix segfault in net_connections().
    • #593: [FreeBSD] Process.memory_maps() segfaults.
    • #606: Process.parent() may swallow NoSuchProcess exceptions.
    • #614: [Linux]: cpu_count(logical=False) return the number of physical CPUs instead of physical cores.
    • #628: [Linux] Process.name() truncates process name in case it contains spaces or parentheses.

    Ease of development

    These are not enhancements you will directly benefit from but I put some effort into making my life easier every time I work on psutil.

    • I care about psutil code being fully PEP8 compliant so I added a pre-commit GIT hook which runs flake8 on every commit and rejects it if the coding style is not compliant. The way I install this is via make install-git-hooks.
    • I added a make install-dev-deps command which installs all deps and stuff which is useful for testing (ipdb, coverage, etc).
    • A new make coverage command which runs coverage. With this I discovered some of parts in the code which weren't covered by tests and I fixed that.
    • I started using tox to easily test psutil against all supported Python versions (from 2.6 to 3.4) in one shot.
    • I reorganized tests so that now they can be easily executed with py.test and nose (before, only unittest runner was fully supported)

    Final words

    I must say I'm pretty satisfied with how psutil is going and the satisfaction I still get every time I work on it. Right now it gets almost 800.000 download a month, which is pretty great for a Python library. As of right now I consider psutil almost "completed" in terms of features, meaning I'm basically running out of ideas on what I should add next (see TODO). From now on the future development will probably focus on adding support for more exotic platforms (OpenBSD, NetBSD, Android). There also have been some discussions on python-ideas mailing list about including psutil into Python stdlib but, assuming that will ever happen, it's still far away in the future as it would require a lot of time which I currently don't have. That should be all. I hope you will all enjoy this new release.

  2. psutil 2.1.2 and Python wheels

    psutil 2.1.2 is out. This release has been cooking for a while now, and that's because I've been travelling for the past 3 months between Spain, Japan and Germany. Hopefully I will be staying in Berlin for a while now, so I will have more time to dedicate to the project. The main new "feature" of this release is that other than the exe files, Windows users can now also benefit of Python wheels (full story is here) which are available on PYPI. Frankly I don't know much about the new wheels packaging system but long story short is that Windows users can now install psutil via pip and therefore also include it as a dependency into requirements.txt. Other than this 2.1.2 can basically be considered a bug-fix release, including some important fixes amongst which:

    • #506: restored Python 2.4 compatibility
    • #340: Process.get_open_files() no longer hangs on Windows (this was a very old and high-priority issue)
    • #501: disk_io_counters() may return negative values on Windows
    • #504: (Linux) couldn't build RPM packages via setup.py

    The list of all fixes can be found here. For the next release I plan to drop support for Python 2.4 and 2.5 and hopefully network interfaces information similarly to ifconfig.

  3. Python and sendfile

    sendfile(2) is a UNIX system call which provides a "zero-copy" way of copying data from one file descriptor (a file) to another (a socket). Because this copying is done entirely within the kernel, sendfile(2) is more efficient than the combination of file.read() and socket.send(), which requires transferring data to and from user space. This copying of the data twice imposes some performance and resource penalties which sendfile(2) syscall avoids; it also results in a single system call (and thus only one context switch), rather than the series of read(2) / write(2) system calls (each system call requiring a context switch) used internally for the data copying. A more exhaustive explanation of how sendfile(2) works is available here, but long story short is that sending a file with sendfile() is usually twice as fast than using plain socket.send(). Typical applications which can benefit from using sendfile() are FTP and HTTP servers.

    socket.sendfile()

    I recently contributed a patch for Python's socket module which adds a high-level socket.sendfile() method (see full discussion at BPO-17552). socket.sendfile() will transmit a file until EOF is reached by attempting to use os.sendfile(), if available, else it falls back on using plain socket.send(). Internally, it takes care of handling socket timeouts and provides two optional parameters to move the file offset or to send only a limited amount of bytes. I came up with this idea because getting all of that right is a bit tricky, so a generic wrapper seemed to be convenient to have. socket.sendfile() will make its appearance in Python 3.5.

    sendfile and Python

    sendfile(2) made its first appearance into the Python stdlib kind of late: Python 3.3. It was contributed by Ross Lagerwall and me in BPO-10882. Since the patch didn't make it into python 2.X and I wanted to use sendfile() in pyftpdlib I later decided to release it as a stand alone module working with older (2.5+) Python versions (see pysendfile project). Starting with version 3.5, Python will hopefully start using sendfile() more extensively, in details:

    Also, Windows provides something similar to sendfile(2): TransmitFile. Now that socket.sendfile() is in place it seems natural to add support for it as well (see BPO-21721).

    Backport to Python 2.6 and 2.7

    For those of you who are interested in using socket.sendfile() with older Python 2.6 and 2.7 versions here's a backport. It requires pysendfile module to be installed. Full code including tests is hosted here.

    #!/usr/bin/env python

"""
This is a backport of socket.sendfile() for Python 2.6 and 2.7.
socket.sendfile() will be included in Python 3.5:
http://bugs.python.org/issue17552
Usage:

>>> import socket
>>> file = open("somefile.bin", "rb")
>>> sock = socket.create_connection(("localhost", 8021))
>>> sendfile(sock, file)
42319283
>>>
"""

import errno
import io
import os
import select
import socket
try:
    memoryview  # py 2.7 only
except NameError:
    memoryview = lambda x: x

if os.name == 'posix':
    import sendfile as pysendfile  # requires "pip install pysendfile"
else:
    pysendfile = None


_RETRY = frozenset((errno.EAGAIN, errno.EALREADY, errno.EWOULDBLOCK,
                    errno.EINPROGRESS))


class _GiveupOnSendfile(Exception):
    pass


if pysendfile is not None:

    def _sendfile_use_sendfile(sock, file, offset=0, count=None):
        _check_sendfile_params(sock, file, offset, count)
        sockno = sock.fileno()
        try:
            fileno = file.fileno()
        except (AttributeError, io.UnsupportedOperation) as err:
            raise _GiveupOnSendfile(err)  # not a regular file
        try:
            fsize = os.fstat(fileno).st_size
        except OSError:
            raise _GiveupOnSendfile(err)  # not a regular file
        if not fsize:
            return 0  # empty file
        blocksize = fsize if not count else count

        timeout = sock.gettimeout()
        if timeout == 0:
            raise ValueError("non-blocking sockets are not supported")
        # poll/select have the advantage of not requiring any
        # extra file descriptor, contrarily to epoll/kqueue
        # (also, they require a single syscall).
        if hasattr(select, 'poll'):
            if timeout is not None:
                timeout *= 1000
            pollster = select.poll()
            pollster.register(sockno, select.POLLOUT)

            def wait_for_fd():
                if pollster.poll(timeout) == []:
                    raise socket._socket.timeout('timed out')
        else:
            # call select() once in order to solicit ValueError in
            # case we run out of fds
            try:
                select.select([], [sockno], [], 0)
            except ValueError:
                raise _GiveupOnSendfile(err)

            def wait_for_fd():
                fds = select.select([], [sockno], [], timeout)
                if fds == ([], [], []):
                    raise socket._socket.timeout('timed out')

        total_sent = 0
        # localize variable access to minimize overhead
        os_sendfile = pysendfile.sendfile
        try:
            while True:
                if timeout:
                    wait_for_fd()
                if count:
                    blocksize = count - total_sent
                    if blocksize <= 0:
                        break
                try:
                    sent = os_sendfile(sockno, fileno, offset, blocksize)
                except OSError as err:
                    if err.errno in _RETRY:
                        # Block until the socket is ready to send some
                        # data; avoids hogging CPU resources.
                        wait_for_fd()
                    else:
                        if total_sent == 0:
                            # We can get here for different reasons, the main
                            # one being 'file' is not a regular mmap(2)-like
                            # file, in which case we'll fall back on using
                            # plain send().
                            raise _GiveupOnSendfile(err)
                        raise err
                else:
                    if sent == 0:
                        break  # EOF
                    offset += sent
                    total_sent += sent
            return total_sent
        finally:
            if total_sent > 0 and hasattr(file, 'seek'):
                file.seek(offset)
else:
    def _sendfile_use_sendfile(sock, file, offset=0, count=None):
        raise _GiveupOnSendfile(
            "sendfile() not available on this platform")


def _sendfile_use_send(sock, file, offset=0, count=None):
    _check_sendfile_params(sock, file, offset, count)
    if sock.gettimeout() == 0:
        raise ValueError("non-blocking sockets are not supported")
    if offset:
        file.seek(offset)
    blocksize = min(count, 8192) if count else 8192
    total_sent = 0
    # localize variable access to minimize overhead
    file_read = file.read
    sock_send = sock.send
    try:
        while True:
            if count:
                blocksize = min(count - total_sent, blocksize)
                if blocksize <= 0:
                    break
            data = memoryview(file_read(blocksize))
            if not data:
                break  # EOF
            while True:
                try:
                    sent = sock_send(data)
                except OSError as err:
                    if err.errno in _RETRY:
                        continue
                    raise
                else:
                    total_sent += sent
                    if sent < len(data):
                        data = data[sent:]
                    else:
                        break
        return total_sent
    finally:
        if total_sent > 0 and hasattr(file, 'seek'):
            file.seek(offset + total_sent)


def _check_sendfile_params(sock, file, offset, count):
    if 'b' not in getattr(file, 'mode', 'b'):
        raise ValueError("file should be opened in binary mode")
    if not sock.type & socket.SOCK_STREAM:
        raise ValueError("only SOCK_STREAM type sockets are supported")
    if count is not None:
        if not isinstance(count, int):
            raise TypeError(
                "count must be a positive integer (got %s)" % repr(count))
        if count <= 0:
            raise ValueError(
                "count must be a positive integer (got %s)" % repr(count))


def sendfile(sock, file, offset=0, count=None):
    """sendfile(sock, file[, offset[, count]]) -> sent

    Send a *file* over a connected socket *sock* until EOF is
    reached by using high-performance sendfile(2) and return the
    total number of bytes which were sent.
    *file* must be a regular file object opened in binary mode.
    If sendfile() is not available (e.g. Windows) or file is
    not a regular file socket.send() will be used instead.
    *offset* tells from where to start reading the file.
    If specified, *count* is the total number of bytes to transmit
    as opposed to sending the file until EOF is reached.
    File position is updated on return or also in case of error in
    which case file.tell() can be used to figure out the number of
    bytes which were sent.
    The socket must be of SOCK_STREAM type.
    Non-blocking sockets are not supported.
    """
    try:
        return _sendfile_use_sendfile(sock, file, offset, count)
    except _GiveupOnSendfile:
        return _sendfile_use_send(sock, file, offset, count)

  4. psutil 2.0

    The time has finally come: psutil 2.0 is out! This is a release which took me a considerable amount of effort and careful thinking during the past 4 months as I went through a major rewrite and reorganization of both python and C extension modules. To get a sense of how much has changed you can compare the differences with old 1.2.1 version by running "hg diff -r release-1.2.1:release-2.0.0" which will produce more than 22,000 lines of output! In those 22k lines I tried to nail down all the quirks the project had accumulated since its start 4 years ago and the resulting code base is now cleaner than ever, more manageable and fully compliant with PEP-7 and PEP-8 guidelines. There were some difficult decisions because many of the changes I introduced are not backward compatible so I was concerned with the pain this may cause existing users. I kind of still am, but I'm sure the transition will be well perceived on the long run as it will result in more manageable user code. OK, enough with the preface and let's see what changed.

    API changes

    I already wrote a detailed blog post about what changed so I recommend you to use that as the official reference on how to port your code.

    RST documentation

    I've never been happy with old doc hosted on Google Code. The markup language provided by Google is pretty limited, plus it's not put under revision control. New doc is more detailed, it uses reStructuredText as the markup language, it lives in the same code repository as psutil's and it is hosted on the excellent readthedocs web site: http://psutil.readthedocs.org/

    Physical CPUs count

    You're now able to distinguish between logical and physical CPUs:

    >>> psutil.cpu_count()  # logical
4
>>> psutil.cpu_count(logical=False)  # physical cores only
2

    Full story is in issue 427.

    Process instances are hashable

    Basically this means process instances can now be checked for equality and can be used with set()s:

    >>> p1 = psutil.Process()
>>> p2 = psutil.Process()
>>> p1 == p2
True
>>> set((p1, p2))
set([<psutil.Process(pid=8217, name='python') at 140007043550608>])

    Full story is in issue 452.

    Speedups

    • #477: process cpu_percent() is about 30% faster.
    • #478: (Linux) almost all APIs are about 30% faster on Python 3.X.

    Other improvements and bugfixes

    • #424: Windows installers for Python 3.X 64-bit
    • #447: psutil.wait_procs() timeout parameter is now optional.
    • #459: a Makefile is now available for running tests and other repetitive tasks (also on Windows)
    • #463: timeout parameter of cpu_percent* functions default to 0.0 because it was a common trap to introduce slowdowns.
    • #340: (Windows) process open_files() no longer hangs.
    • #448: (Windows) fixed a memory leak affecting children() and ppid() methods.
    • #461: namedtuples are now pickle-able.
    • #474: (Windows) Process.cpu_percent() is no longer capped at 100%

    OK, that's all folks. I hope you will enjoy this new version and report your feedback.

  5. Reimplementing netstat in Python

    psutil 2.1.0 is out and with it I finally managed to implement something I've been wanting to have for a long time: netstat-like functionalities (see ticket). Similarly to "netstat -antp" on UNIX you can now list system-wide connections in pure python and also determine what process (PID) is using a particular connection:

    >>> import psutil
>>> from pprint import pprint as pp
>>> pp(psutil.net_connections())
[sconn(fd=-1, family=2, type=1, laddr=('127.0.0.1', 587), raddr=(), status='LISTEN', pid=None),
 sconn(fd=-1, family=2, type=1, laddr=('127.0.0.1', 6379), raddr=(), status='LISTEN', pid=None),
 sconn(fd=-1, family=2, type=1, laddr=('127.0.1.1', 53), raddr=(), status='LISTEN', pid=None),
 sconn(fd=-1, family=2, type=1, laddr=('10.0.3.1', 53), raddr=(), status='LISTEN', pid=None),
 sconn(fd=-1, family=2, type=1, laddr=('127.0.0.1', 631), raddr=(), status='LISTEN', pid=None),
 sconn(fd=-1, family=2, type=1, laddr=('127.0.0.1', 25), raddr=(), status='LISTEN', pid=None),
 sconn(fd=-1, family=2, type=1, laddr=('0.0.0.0', 3389), raddr=(), status='LISTEN', pid=None),
 sconn(fd=17, family=2, type=1, laddr=('127.0.0.1', 34785), raddr=(), status='LISTEN', pid=3591),
 sconn(fd=15, family=2, type=1, laddr=('127.0.0.1', 56359), raddr=(), status='LISTEN', pid=3591),
 sconn(fd=-1, family=10, type=2, laddr=('::', 56720), raddr=(), status='NONE', pid=None)]
>>>

    This is yet another functionality which can be used for monitoring purposes. For example, say you want to make sure your HTTP server is running on port 80, you can do something like this:

    import psutil

def check_listening_port(port):
    """Return True if the given TCP port is busy and in LISTEN mode."""
    for conn in psutil.net_connections(kind='tcp'):
        if conn.laddr[1] == port and conn.status == psutil.CONN_LISTEN:
            return True
    return False

print(check_listening_port(80))

    Netstat in pure python

    Here it is, in 65 lines of code: netstat.py. Pretty neat right? ;-)

    Implementation(s)

    As always, each platform required its own, different, implementation. Luckily for some platforms (OSX, Windows) I was able to reuse and customize some code from the existing Process.connections() implementation which was already in place. For those of you who are interested in knowing how this was done here's the source code references:

    Hopefully this will help whoever needs to do this into another language. The only platform where this is sort of clunky is OSX, which does not expose anything to list all system-wide sockets in a single shot, so you're forced to query each process. That means you'll need root privileges otherwise you'll get an access denied error. For what it's worth, I took a look at lsof and it has the same limitation and netstat runs with SUID. Well, I guess this is it. I'll leave you with some docs. For the next one I'm planning on working on a couple of other network-related functionalities: "ifconfig" and NIC speeds. But that's for another time...

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