Adding arguments to __init__ of ConfigParser

Question

I want to extend SafeConfigParser with some functionality by inheriting from it:

class ExtendedConfigParser(SafeConfigParser):

    def __init__(self, *args, **kwargs):
        SafeConfigParser.__init__(self, *args, **kwargs)

..but have a problem with SafeConfigParser's init:

    SafeConfigParser.__init__(self, *args, **kwargs)
TypeError: __init__() got an unexpected keyword argument 'config_file'

I could get around the problem by deleting added kw arguments from kwargs, but I wonder if there is a more elegant solution? (note: it seems that SafeConfigParser is an old-style class).

Answer 1

I assume you're inheriting from Python's SafeConfigParser and you're trying to instantiate ExtendedConfigParser like this:

cfg_parser = ExtendedConfigParser(config_file='my_file.cfg')

If that's the case, then SafeConfigParser doesn't have any keyword argument named config_file which is where the error is coming from.

A function declaration in python allows you to specify arguments, keyword arguments, and then it allows unspecified arguments and keyword arguments through *args and **kwargs . I'm assuming you're wanting to access config_file only in ExtendedConfigParser and not in SafeConfigParser .

All you need to do is change your __init__ parameters in ExtendedConfigParser :

class ExtendedConfigParser(SafeConfigParser):

    def __init__(config_file='', *args, **kwargs):
        self.config_file = config_file
        SafeConfigParser.__init__(self, *args, **kwargs)

This allows you specify any needed parameters for ExtendedConfigParser and then passes any additional parameters on to SafeConfigParser 's constructor.