I'm writing some report generation code, where a class CoverageReporter is doing all of the heavy lifting, with just a few attributes changing between different instances of CoverageReporter. Let's say we want to alias

SubsystemCoverageReporter(*args, **kwargs)

to

CoverageReporter('subsystem', *args, **kwargs)

in a concise way. Currently, I accomplish it like so:

class SubsystemCoverageReporter(object):
    def __init__(self, *args, **kwargs):
        self.reporter = CoverageReporter('subsystem', *args, **kwargs)

    def __getattr__(self, name):
        return getattr(self.reporter, name)

Another one, subsystem 2, has almost exactly the same boilerplate, eg:

class SubsystemTwoCoverageReporter(object):
    def __init__(self, *args, **kwargs):
        self.reporter = CoverageReporter('subsystem2', *args, **kwargs)

    def __getattr__(self, name):
        return getattr(self.reporter, name)

Is there a more concise Pythonic way to express this? I'd prefer not to rely on inheritance, but if there's no better ways I'm open to that.

CodePudding user response：

Say you had your class CoverageReporter like so:

class CoverageReporter:
    def __init__(self, _type, _name):
        self.type = _type
        self.name = _name
        
    def do_something(self):
        print(f"{self.type}:{self.name} did something")
        
    def do_something_else(self):
        print(f"{self.type}:{self.name} did something else")     

You could define a function which creates the CoverageReporter and returns that object.

def SubsystemCoverageReporter(*args, **kwargs):
    return CoverageReporter('subsystem', *args, **kwargs)


def SubsystemTwoCoverageReporter(*args, **kwargs):
    return CoverageReporter('subsystem2', *args, **kwargs)

s1 = SubsystemCoverageReporter("Foo")
s2 = SubsystemTwoCoverageReporter("Bar")

s1.do_something()         # subsystem:Foo did something
s2.do_something_else()    # subsystem2:Bar did something else

Note that this isn't exactly equivalent to what you have, since SubsystemCoverageReporter isn't a class, so you won't be able to inherit it. If you want that option available, then off the top of my head I think inheritance is the best solution you have.

class SubsystemCoverageReporter(CoverageReporter):
    def __init__(self, *args, **kwargs):
        super().__init__('subsystem', *args, **kwargs)
        
class SubsystemTwoCoverageReporter(CoverageReporter):
    def __init__(self, *args, **kwargs):
        super().__init__('subsystem2', *args, **kwargs)

s1 = SubsystemCoverageReporter("Foo")
s2 = SubsystemTwoCoverageReporter("Bar")

s1.do_something()         # subsystem:Foo did something
s2.do_something_else()    # subsystem2:Bar did something else

CodePudding user response：

If you want to avoid repeating yourself, use the same solution you always would, wrap the repeated code in a function and parameterize the parts that can change:

def make_klass(subsystem):
    class SubsystemCoverageReporter(object):
        def __init__(self, *args, **kwargs):
            self.reporter = CoverageReporter(subsystem, *args, **kwargs)
    
        def __getattr__(self, name):
            return getattr(self.reporter, name)
    return SubsystemCoverageReporter


SubsystemCoverageReporter = make_klass("subsystem")
SubsystemTwoCoverageReporter = make_klass("subsystem2")

Note, the classes you create will have the same value for their __name__ attribute. That is hopefully not important, but you can get around it, e.g.:

SubsystemCoverageReporter.name = "SubsystemCoverageReporter" SubsystemTwoCoverageReporter.name = "SubsystemTwoCoverageReporter"

Although that is ugly.

You could use the type constructor directly, or if metaclasses are an issue, use types.new_class instead and it will handle it correctly. But in the simplest case,

def make_klass(name, subsystem):
    def __init__(self, *args, **kwargs):
        self.reporter = CoverageReporter(subsystem, *args, **kwargs)
    def __getattr__(self, name):
        return getattr(self.reporter, name)
    klass = type(name, (object,), dict(__init__=__init__, __getattr__=__getattr__))
    return klass

SubsystemCoverageReporter = make_klass("SubsystemCoverageReporter", "subsystem")
SubsystemTwoCoverageReporter = make_klass("SubsystemTwoCoverageReporter", "subsytem2")

Although note, you are repeating yourself here a little.

But again, normally you shouldn't care about the __name__ attribute