Frequently Asked Questions / Usage tips for PyLint
==================================================


Question:
  Is it possible to give file as argument to pylint, instead of module ?

Answer:
  pylint expects the name of a package or module as argument. As a convenience,
  you can give to it a file name if it's possible to guess a module name from
  the file's path, using the python path. Some examples :

  "pylint mymodule.py" should always works since the current working
  directory is automatically added on top  of the python path

  "pylint directory/mymodule.py" will work if "directory" is a python
  package (i.e. has an __init__.py file) or if "directory" is in the
  python path.

  "pylint /whatever/directory/mymodule.py" will work if either:

    - "/whatever/directory" is in the python path

    - your cwd is "/whatever/directory"

    - "directory" is a python package and "/whatever" is in the python
      path

    - "directory" is a python package and your cwd is "/whatever"
      and so on...



Question:
  I'm using psyobj from psyco_ and get a lot of spurious "unused variables
  messages". Is it normal ?

Answer: 
  Yes. That's actually due to a bug in psyco, making the locals()
  function for objects inheriting from *psyobj* returning an empty
  dictionary. For the moment, the only way to fix this is to use the
  PYLINT_IMPORT environment variable to not use psyco during pylint
  checking. Sample code ::

    import os
    try:
        if os.environ.has_key('PYLINT_IMPORT'):
            raise ImportError()
	from psyco.classes import psyobj
    except ImportError:
	    class psyobj:
	        pass

  NOTICE: this problem should not occurs with pylint >= 0.5 since from
  this version pylint is not looking anymore for information in living
  objects (i.e. it doesn't anymore import analysed modules)



Question:
  I've a function / method which is a callback where I do not have any
  control on received argument, and pylint is complaining about unused
  arguments. What can I do to avoid those warnings ?

Answer:
  prefix (ui) the callback's name by `cb_`, as in cb_onclick(...). By
  doing so arguments usage won't be checked. Another solution is to
  use one of the name defined in the "dummy-variables" configuration
  variable for unused argument ("_" and "dummy" by default).



Question:
  When pylint is considering a class as an interface ?

Answer:
  A class is considered as an interface if there is a class named
  "Interface" somewhere in it ancestor's tree.



Question:
  When pylint is considering that a class is implementing a given
  interface ?

Answer:
  Pylint is using the Zope 2 interfaces conventions, and so is
  considering that a class is implementing interfaces listed in its
  __implements__ attribute.



Question:
  When pylint is considering a class as an abstract class ?

Answer:
  A class is considered as an abstract class if at least one of its
  methods is doing nothing but raising NotImplementedError



Question:
  Is there some way to disable some message for a particular module
  only ?

Answer:
  Yes, you can disable or enable (globally disabled) message at the
  module level by adding the corresponding option in a comment at the
  top of the file: ::

    # pylint: disable-msg=W0401, E0202
    # pylint: enable-msg=C0302



Question:
  I've a mixin class relying on attributes of the mixed class, and I
  would like to not have the "access to undefined member" message on
  this class. Is it possible ?

Answer:
  Yes :o) To do so you have to set the ignore-mixin-members option to
  "yes" (this is the default value) and to name your mixin class with
  a name which ends with "mixin" (whatever case)



Question:
  Is it possible to locally disabling a particular message for a block
  of code or for a single line of code ?
Answer:
  Yes, this feature has been added in pylint 0.11. This may be done by
  adding "#pylint: disable-msg=W0123,E4567" at the desired block level
  or at the end of the desired line of code



Question:
  Where are stored persistent data necessary to make comparison between
   to successive run ?

Answer:
  Analysis data are stored as pickle file in a directory which is 
  localized using the following rules:

  * value of the PYLINTHOME environment variable if set

  * ".pylint.d" subdirectory of the user's home directory if it is found
    (not always findable on Windows platforms)

  * ".pylint.d" directory in the current directory


.. _psyco: http://psyco.sf.net