blog entries created by Sylvain Thenault
show 42 results
  • Helping pylint to understand things it doesn't

    2011/10/10 by Sylvain Thenault

    The latest release of logilab-astng (0.23), the underlying source code representation library used by PyLint, provides a new API that may change pylint users' life in the near future...

    It aims to allow registration of functions that will be called after a module has been parsed. While this sounds dumb, it gives a chance to fix/enhance the understanding PyLint has about your code.

    I see this as a major step towards greatly enhanced code analysis, improving the situation where PyLint users know that when running it against code using their favorite framework (who said CubicWeb? :p ), they should expect a bunch of false positives because of black magic in the ORM or in decorators or whatever else. There are also places in the Python standard library where dynamic code can cause false positives in PyLint.

    The problem

    Let's take a simple example, and see how we can improve things using the new API. The following code:

    import hashlib
    def hexmd5(value):
        """"return md5 checksum hexadecimal digest of the given value"""
        return hashlib.md5(value).hexdigest()
    def hexsha1(value):
        """"return sha1 checksum hexadecimal digest of the given value"""
        return hashlib.sha1(value).hexdigest()

    gives the following output when analyzed through pylint:

    [syt@somewhere ~]$ pylint -E
    No config file found, using default configuration
    ************* Module smarter_astng
    E:  5,11:hexmd5: Module 'hashlib' has no 'md5' member
    E:  9,11:hexsha1: Module 'hashlib' has no 'sha1' member


    [syt@somewhere ~]$ python
    Python 2.7.1+ (r271:86832, Apr 11 2011, 18:13:53)
    [GCC 4.5.2] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import smarter_astng
    >>> smarter_astng.hexmd5('hop')
    >>> smarter_astng.hexsha1('hop')

    The code runs fine... Why does pylint bother me then? If we take a look at the hashlib module, we see that there are no sha1 or md5 defined in there. They are defined dynamically according to Openssl library availability in order to use the fastest available implementation, using code like:

    for __func_name in __always_supported:
        # try them all, some may not work due to the OpenSSL
        # version not supporting that algorithm.
            globals()[__func_name] = __get_hash(__func_name)
        except ValueError:
            import logging
            logging.exception('code for hash %s was not found.', __func_name)

    Honestly I don't blame PyLint for not understanding this kind of magic. The situation on this particular case could be improved, but that's some tedious work, and there will always be "similar but different" case that won't be understood.

    The solution

    The good news is that thanks to the new astng callback, I can help it be smarter! See the code below:

    from logilab.astng import MANAGER, scoped_nodes
    def hashlib_transform(module):
        if == 'hashlib':
            for hashfunc in ('sha1', 'md5'):
                module.locals[hashfunc] = [scoped_nodes.Class(hashfunc, None)]
    def register(linter):
        """called when loaded by pylint --load-plugins, register our tranformation
        function here

    What's in there?

    • A function that will be called with each astng module built during a pylint execution, i.e. not only the one that you analyses, but also those accessed for type inference.
    • This transformation function is fairly simple: if the module is the 'hashlib' module, it will insert into its locals dictionary a fake class node for each desired name.
    • It is registered using the register_transformer method of astng's MANAGER (the central access point to built syntax tree). This is done in the pylint plugin API register callback function (called when module is imported using 'pylint --load-plugins'.

    Now let's try it! Suppose I stored the above code in a '' module in my PYTHONPATH, I can now run pylint with the plugin activated:

    [syt@somewhere ~]$ pylint -E --load-plugins astng_hashlib
    No config file found, using default configuration
    ************* Module smarter_astng
    E:  5,11:hexmd5: Instance of 'md5' has no 'hexdigest' member
    E:  9,11:hexsha1: Instance of 'sha1' has no 'hexdigest' member

    Huum. We have now a different error :( Pylint grasp there are some md5 and sha1 classes but it complains they don't have a hexdigest method. Indeed, we didn't give a clue about that.

    We could continue on and on to give it a full representation of hashlib public API using the astng nodes API. But that would be painful, trust me. Or we could do something clever using some higher level astng API:

    from logilab.astng import MANAGER
    from logilab.astng.builder import ASTNGBuilder
    def hashlib_transform(module):
        if == 'hashlib':
        fake = ASTNGBuilder(MANAGER).string_build('''
    class md5(object):
      def __init__(self, value): pass
      def hexdigest(self):
        return u''
    class sha1(object):
      def __init__(self, value): pass
      def hexdigest(self):
        return u''
        for hashfunc in ('sha1', 'md5'):
            module.locals[hashfunc] = fake.locals[hashfunc]
    def register(linter):
        """called when loaded by pylint --load-plugins, register our tranformation
        function here

    The idea is to write a fake python implementation only documenting the prototype of the desired class, and to get an astng from it, using the string_build method of the astng builder. This method will return a Module node containing the astng for the given string. It's then easy to replace or insert additional information into the original module, as you can see in the above example.

    Now if I run pylint using the updated plugin:

    [syt@somewhere ~]$ pylint -E --load-plugins astng_hashlib
    No config file found, using default configuration

    No error anymore, great!

    What's next?

    This fairly simple change could quickly provide great enhancements. We should probably improve the astng manipulation API now that it's exposed like that. But we can also easily imagine a code base of such pylint plugins maintained by each community around a python library or framework. One could then use a plugins stack matching stuff used by its software, and have a greatly enhanced experience of using pylint.

    For a start, it would be great if pylint could be shipped with a plugin that explains all the magic found in the standard library, wouldn't it? Left as an exercice to the reader!

  • Pylint 0.24 / logilab-astng 0.22

    2011/07/21 by Sylvain Thenault

    Hi there!

    I'm pleased to announce new releases of pylint and its underlying library logilab-astng. See and for more info.

    Those releases include mostly fixes and a few enhancements. Python 2.6 relative / absolute imports should now work fine and Python 3 support has been enhanced. There are still two remaining failures in astng test suite when using python 3, but we're unfortunatly missing resources to fix them yet.

    Many thanks to everyone who contributed to this release by submitting patches or by participating to the latest bugs day.

  • pylint bug day #3 on july 8, 2011

    2011/07/04 by Sylvain Thenault

    Hey guys,

    we'll hold the next pylint bug day on july 8th 2011 (friday). If some of you want to come and work with us in our Paris office, you'll be welcome.

    You can also join us on jabber / irc:

    I know the announce is a bit late, but I hope some of you will be able to come or be online anyway!

    Regarding the program, the goal is to decrease the number of tickets in the tracker. I'll try to do some triage earlier this week so you'll get a chance to talk about your super-important ticket that has not been selected. Of course, if you intend to work on it, there is a bigger chance of it being fixed next week-end ;)

  • pylint bug days #2 report

    2010/04/19 by Sylvain Thenault

    First of all, I've to say that pylint bugs day wasn't that successful in term of 'community event': I've been sprinting almost alone. My Logilab's felows were tied to customer projects, and no outside people shown up on jabber. Fortunatly Tarek Ziade came to visit us, and that was a nice opportunity to talk about pylint, distribute, etc ... Thank you Tarek, you saved my day ;)

    As I felt a bit alone, I decided to work on somethings funnier than bug fixing: refactoring!

    First, I've greatly simplified the command line: enable-msg/enable-msg-cat/enable-checker/enable-report and their disable-* counterparts were all merged into single --enable/--disable options.

    I've also simplified "pylint --help" output, providing a --long-help option to get what we had before. Generic support in `logilab.common.configuration of course.

    And last but not least, I refactored pylint so we can have multiple checkers with the same name. The idea behind this is that we can split checker into smaller chunks, basically only responsible for one or a few related messages. When pylint runs, it only uses necessary checkers according to activated messages and reports. When all checkers will be splitted, it should improve performance of "pylint --error-only".

    So, I can say I'm finally happy with the results of that pylint bugs day! And hopefuly we will be more people for the next edition...

  • pylint bugs day #2 on april 16, 2010

    2010/03/22 by Sylvain Thenault

    Hey guys,

    we'll hold the next pylint bugs day on april 16th 2010 (friday). If some of you want to come and work with us in our Paris office, you'll be much welcome.

    Else you can still join us on jabber / irc:

    See you then!

  • pylint bug day next wednesday!

    2009/11/23 by Sylvain Thenault

    Remember that the first pylint bug day will be held on wednesday, november 25, from around 8am to 8pm in the Paris (France) time zone.

    We'll be a few people at Logilab and hopefuly a lot of other guys all around the world, trying to make pylint better.

    Join us on the #public conference room of, or if you prefer using an IRC client, join #public on which is a gateway to the jabber forum. And if you're in Paris, come to work with us in our office.

    People willing to help but without knowledge of pylint internals are welcome, it's the perfect occasion to learn a lot about it, and to be able to hack on pylint in the future!

  • First Pylint Bug Day on Nov 25th, 2009 !

    2009/10/21 by Sylvain Thenault

    Since we don't stop being overloaded here at Logilab, and we've got some encouraging feedback after the "Pylint needs you" post, we decided to take some time to introduce more "community" in pylint.

    And the easiest thing to do, rather sooner than later, is a irc/jabber synchronized bug day, which will be held on Wednesday november 25. We're based in France, so main developpers will be there between around 8am and 19pm UTC+1. If a few of you guys are around Paris at this time and wish to come at Logilab to sprint with us, contact us and we'll try to make this possible.

    The focus for this bug killing day could be:

    • using tracker : getting an account, submitting tickets, triaging existing tickets...
    • using mercurial to develop pylint / astng
    • guide people in the code so they're able to fix simple bugs

    We will of course also try to kill a hella-lotta bugs, but the main idea is to help whoever wants to contribute to pylint... and plan for the next bug-killing day !

    As we are in the process of moving to another place, we can't organize a sprint yet, but we should have some room available for the next time, so stay tuned :)

  • New pylint/astng release, but... pylint needs you !

    2009/08/27 by Sylvain Thenault

    After several months with no time to fix/enhance pylint beside answering email and filing tickets, I've finally tackled some tasks yesterday night to publish bug fixes releases ([1] and [2]).

    The problem is that we don't have enough free time at Logilab to lower the number of tickets in pylint tracker page . If you take a look at the ticket tab, you'll see a lot of pendings bug and must-have features (well, and some other less necessary...). You can already easily contribute thanks to the great mercurial dvcs, and some of you do, either by providing patches or by reporting bugs (more tickets, iiirk ! ;) Thank you all btw !!

    Now I was wondering what could be done to make pylint going further, and the first ideas which came to my mind was :

    • do ~3 days sprint
    • do some 'tickets killing' days, as done in some popular oss projects

    But for this to be useful, we need your support, so here are some questions for you:

    • would you come to a sprint at Logilab (in Paris, France), so you can meet us, learn a lot about pylint, and work on tickets you wish to have in pylint?
    • if France is too far away for most people, would you have another location to propose?
    • would you be on jabber for a tickets killing day, providing it's ok with your agenda? if so, what's your knowledge of pylint/astng internals?

    you may answer by adding a comment to this blog (please register first by using the link at the top right of this page) or by mail to If we've enough positive answers, we'll take the time to organize such a thing.

  • iclassmethod decorator to define both a class and an instance method in one go

    2009/04/28 by Sylvain Thenault

    You'll find in the logilab.common.decorators module the iclassmethod decorator which may be pretty handy in some cases as it allows methods to be both called as class methods or as instance methods. In the first case the first argument will be the class and the second case it will be the instance.

    Example extracted (and adapted for simplicity) from CubicWeb:

    from logilab.common.decorators import iclassmethod
    class Form(object):
      _fields_ = []
      def __init__(self):
          self.fields = list(self._fields_)
      def field_by_name(cls_or_self, name):
          """return field with the given name and role"""
          if isinstance(cls_or_self, type):
              fields = cls_or_self._fields_
              fields = cls_or_self.fields
          for field in fields:
              if == name:
                  return field
          raise Exception('FieldNotFound: %s' % name)

    Example session:

    >>> from logilab.common import attrdict
    >>> f = Form()
    >>> f.fields.append(attrdict({'name': 'something', 'value': 1})
    >>> f.field_by_name('something')
    {'name': 'something', 'value': 1}
    >>> Form.field_by_name('something')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "<stdin>", line 15, in field_by_name
    Exception: FieldNotFound: something

    So we get a field_by_name method which will act differently (actually use different input data) when called as instance method or as class method.

    Also notice the attrdict trick that can also be achieved with the Python 2.6 named tuple.

  • new pylint / astng / common releases

    2009/03/25 by Sylvain Thenault

    I'm pleased to announce releases of pylint 0.18, logilab-astng 0.19 and logilab-common 0.39. All these packages should now be cleanly available through easy install.

    Also, happy pylint users will get:

    • fixed python 2.6 support (pylint/astng tested from 2.4 to 2.6)
    • get source code (and so astng) for zip/egg imports
    • some understanding of the property decorator and of unbound methods
    • some false positives fixed and others minor improvments

    See projects home page and ChangeLog for more information:

    Please report any problem / question to the mailing-list.


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