Configuring an object via a dictionary
Thomas Passin
list1 at tompassin.net
Fri Mar 15 15:48:17 EDT 2024
On 3/15/2024 3:09 PM, Grant Edwards via Python-list wrote:
> On 2024-03-15, Thomas Passin via Python-list <python-list at python.org> wrote:
>> On 3/15/2024 5:30 AM, Loris Bennett via Python-list wrote:
>>> Hi,
>>>
>>> I am initialising an object via the following:
>>>
>>> def __init__(self, config):
>>>
>>> self.connection = None
>>>
>>> self.source_name = config['source_name']
>>> self.server_host = config['server_host']
>>> self.server_port = config['server_port']
>>> self.user_base = config['user_base']
>>> self.user_identifier = config['user_identifier']
>>> self.group_base = config['group_base']
>>> self.group_identifier = config['group_identifier']
>>> self.owner_base = config['owner_base']
>>>
>>> However, some entries in the configuration might be missing. What is
>>> the best way of dealing with this?
>>>
>>> I could of course simply test each element of the dictionary before
>>> trying to use. I could also just write
>>>
>>> self.config = config
>>>
>>> but then addressing the elements will add more clutter to the code.
>>>
>>> However, with a view to asking forgiveness rather than
>>> permission, is there some simple way just to assign the dictionary
>>> elements which do in fact exist to self-variables?
>>>
>>> Or should I be doing this completely differently?
>>
>> self.source_name = config.get('source_name', default_value)
>>
>> Or, if you like this kind of expression better,
>>
>> self.source_name = config.get('source_name') or default_value
>
> Won't the latter version misbehave if the value of config['source_name'] has a
> "false" boolean value (e.g. "", 0, 0.0, None, [], (), {}, ...)
>
>>>> config = {}
>>>> config['source_name'] = ""
>>>> config.get('source_name') or 'default'
> 'default'
Oh, well, picky, picky! I've always like writing using the "or" form
and have never gotten bit - especially for configuration-type values
where you really do expect a non-falsey value, it's probably low risk -
but of course, you're right. In newer code I have been putting a default
into get(). And I suppose there is always the possibility that sometime
in the future an "or" clause like that will be changed to return a
Boolean, which one would expect anyway.
More information about the Python-list
mailing list