Re: What is more Pythonic: subclass or adding functionality to base class?

[Paul Moore]

On 11 February 2018 at 12:55, D'Arcy Cain  wrote:
> On 02/11/18 06:30, Victor Porton wrote:
>> What is more pythonic?
>>
>> 1. Create its subclass PredicateParserWithError and add the additional field
>> on_error to this class.
>>
>> 2. Add on_error field to the base class, setting it to None by default, if
>> the class's user does not need this field.
>
> Personally I would go with #1.  It just seems cleaner.  Not sure what
> the Python gods would do.

I don't know about "Python Gods" or even what's more Pythonic, but it
might be worth commenting that if this were Java, adding a new field
to the base class would need every file that used the class to be
recompiled. So there's a tendency to subclass just to minimise the
impact of a change like this. In Python, that's not necessary, as
classes are created at runtime, and there's no compile-time layout
that code needs to depend on, so if you add an extra field to a class,
only those parts of your codebase that need the new field have to
care.

Of course, if this is a public API, backward compatibility and
versioning of the API become issues, that may affect your decision.
Paul
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Re: What is more Pythonic: subclass or adding functionality to base class?

[D'Arcy Cain]

On 02/11/18 06:30, Victor Porton wrote:
> What is more pythonic?
> 
> 1. Create its subclass PredicateParserWithError and add the additional field 
> on_error to this class.
> 
> 2. Add on_error field to the base class, setting it to None by default, if 
> the class's user does not need this field.

Personally I would go with #1.  It just seems cleaner.  Not sure what
the Python gods would do.

-- 
D'Arcy J.M. Cain
Vybe Networks Inc.
http://www.VybeNetworks.com/
IM:da...@vex.net VoIP: sip:da...@vybenetworks.com
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What is more Pythonic: subclass or adding functionality to base class?

[Victor Porton]

The following is a real code fragment:

##
class PredicateParser(object, metaclass=ABCMeta):
"""
Parses a given predicate (which may participate in several 
relationships)
of a given RDF node.
"""

def __init__(self, predicate):
self.predicate = predicate

@abstractmethod
def parse(self, parse_context, graph, node):
pass
##

Now I need to add new field on_error (taking one of three enumerated values) 
to some objects of this class.

What is more pythonic?

1. Create its subclass PredicateParserWithError and add the additional field 
on_error to this class.

2. Add on_error field to the base class, setting it to None by default, if 
the class's user does not need this field.

-- 
Victor Porton - http://portonvictor.org
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