ConfigParser getters not available on SectionProxy #62359

Activity

1. jbvsmo commented on Jun 7, 2013

   

   jbvsmomannequin

   on Jun 7, 2013

   MannequinAuthor

   More actions

   The configparser.RawConfigParser class implements some get methods:
   get, getint, getfloat, getboolean

   but if any of these get overridden on a subclass(with other arguments) or new ones are added (e.g. getlist), there's no way a SectionProxy instance will be able to use them.

       class DemoParser(ConfigParser):
           def getlist(self, section, option):
               return self.get(section, option).split()
   
       parser = DemoParser()
       parser.read(some_file)
   
       # These 2 lines should be equivalent, like "getint", but the
       # second doesn't work because of the SectionProxy instance
       parser.getlist('some_section', 'foo')
       parser['some_section'].getlist('foo')

   Reading the code, for SectionProxy, it redefines all the get* methods from RawConfigParser, and that looks pretty bad...

   A more elegant approach would be to fetch the function on the parser instance and bound to the section name with lambda or functools.partial... Something like:

       class SectionProxy(...):
           ...
           
           def __getattr__(self, attr):
               if not attr.startswith('get'):
                   raise AttributeError(attr)
               fn = getattr(self._parser, attr)
               return lambda *args, **kw: fn(self._name, *args, **kw)
2. jbvsmo

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Jun 7, 2013
3. ambv commented on Jun 7, 2013

   

   ambv

   on Jun 7, 2013

   Contributor

   More actions

   This is a reasonable feature request. Overriding __getattr__ doesn't look like the best solution, though. Let me think this over.
4. ambv

   self-assigned this

   on Jun 7, 2013
5. jbvsmo commented on Jun 8, 2013

   

   jbvsmomannequin

   on Jun 8, 2013

   MannequinAuthor

   More actions

   Overriding __getattr__ doesn't look like the best solution

   Another idea would be to allow the proxy class to be selectable, but this would require the user to do much more coding for this simple thing...

   I believe a proxy should be dynamic enough to avoid having to duplicate every function definition.
6. ambv commented on Jun 25, 2013

   

   ambv

   on Jun 25, 2013

   Contributor

   More actions

   There are several reasons why get*() methods are redefined on the section proxy. First of all, explicit is better than implicit. Secondly, the order of arguments is different: parser.get() has the fallback argument as the last (and keyword-only), whereas parser['section'].get() behaves like a mapping. You can do parser['section'].get('key', 'some-fallback-value') and parser['section'].get('no-such-key') returns None instead of raising NoOptionError.

   This makes it difficult to automagically support parser get*() methods on the section proxy. This is why I decided to adapt a different mechanism: register a converter and a getter is automatically available:

     >>> cp = ConfigParser()
     >>> cp.converters['list'] = lambda value: value.strip().split()
     >>> cp.getlist('section', 'l')
     ['a', 'b', 'c']
     >>> cp['section'].getlist('l')
     ['a', 'b', 'c']
     >>> cp.getdict('section', 'd')
     Traceback (most recent call last):
     ...
     AttributeError: 'ConfigParser' object has no attribute 'getdict'
     >>> cp['section'].getdict('d')
     Traceback (most recent call last):
     ...
     AttributeError: 'ConfigParser' object has no attribute 'getdict'

   This ensures that you can easily add new converters in subclasses or single instances and that the parser-level API and section-level API work like they should. This also makes implementing custom getters easier since there's no logic involved besides the conversion. And if you happen to need custom logic anyway, you can register a converter that is a callable class.
7. ambv

   added

   type-featureA feature request or enhancementA feature request or enhancement

   and removed

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Jun 25, 2013
8. jbvsmo commented on Jul 17, 2013

   

   jbvsmomannequin

   on Jul 17, 2013

   MannequinAuthor

   More actions

   Was the patch accepted yet? Looks good to me
9. jbvsmo commented on Apr 17, 2014

   

   jbvsmomannequin

   on Apr 17, 2014

   MannequinAuthor

   More actions

   ping?
10. ambv commented on Sep 15, 2014

    

    ambv

    on Sep 15, 2014

    Contributor

    More actions

    The reason I didn't commit that patch before was that I wasn't sure whether making this change wouldn't create any unexpected backwards incompatibility.

    In fact, if I committed the patch as is, it would. I solved this by leaving getint, getfloat and getboolean on the parser class and keeping _get in use.
11. ambv commented on Sep 15, 2014

    

    ambv

    on Sep 15, 2014

    Contributor

    More actions

    The new implementation also automatically covers get*() methods added on subclasses, no need to use converters= in that case.
12. python-dev commented on Sep 15, 2014

    

    python-devmannequin

    on Sep 15, 2014

    Mannequin

    More actions

    New changeset 2c46a4ded259 by Łukasz Langa in branch 'default':
    Closes bpo-18159: ConfigParser getters not available on SectionProxy
    https://hg.python.org/cpython/rev/2c46a4ded259

    New changeset 5eb95d41ee43 by Łukasz Langa in branch 'default':
    Closes bpo-18159: ConfigParser getters not available on SectionProxy
    https://hg.python.org/cpython/rev/5eb95d41ee43
13. python-dev

    closed this as completedon Sep 15, 2014
14. ezio-melotti

    transferred this issue fromon Apr 10, 2022