Question

I’ve written some code that allows the term ‘job’ to be used universally to perform a unique task. The specific jobs can be chosen through setting an initial variable “job_type”. From that initial variable a particulay subclass is chosen to perform the appropriate job. Maybe the code will make more sense 🙂

if __name__=='__main__':
    # these variables would normally be called in from a config file
    job_type = 'job1'
    uni_var = 10

    job_select = superClass(job_type, uni_var)
    job_select.job()        


class superClass(object):
    def __init__(self, job_type, uni_var):
        self.job_type = job_type   
        self.uni_var = uni_var

        if self.job_type == 'job1':
            self.jobChoice = option1()
        else:
            self.jobChoice = option2()

    # This is the definition called by the main function it then
    # redirects the request to the appropriate job sub class   
    def job(self):
        self.jobChoice.job()

class option1(superClass):
    def __init__(self):
        pass

    def job(self):
        print 'job option 1'
        print uni_var

class option2(superClass):
    def __init__(self):
        pass

    def job(self):
        print 'job option 2'
        print uni_var

The thought behind this code was to allow a single/constant ‘main’ function, to action a variety of unique tasks based purely on the variable ‘job_type’. Which it seems to be doing fine.

My question (as a very inexperienced coder) is, have I gone about this the right way or is there a better way to do things?

Also, have I set up the variable ‘uni_var’ correctly in the superClass to be correctly shared across all/any superClass subclasses?

Thanks.

Answer 1

I suspect that what you really want is to use the Factory Method Pattern here.

You could change your code to something like this:

if __name__=='__main__':
    # these variables would normally be called in from a config file
    job_type = 'job1'
    uni_var = 10

    job_select = superClass.optionFactory(job_type, uni_var)
    job_select.job()        


class superClass(object):
    def __init__(self, job_type, uni_var):
        self.job_type = job_type   
        self.uni_var = uni_var

    # This is the definition called by the main function it then
    # redirects the request to the appropriate job sub class   
    def job(self):
        raise NotImplementedError()

    @staticmethod
    def optionFactory(job_type, uni_var):
        "Return an instance of superClass based on job_type and uni_var."
        if job_type == "job1":
            return option1(job_type, uni_var)
        else:
            return option2(job_type, uni_var)

class option1(superClass):
    def __init__(self, job_type, uni_var):
        super(option1, self).__init__(job_type, uni_var)

    def job(self):
        print 'job option 1'
        print uni_var

class option2(superClass):
    def __init__(self, job_type, uni_var):
        super(option2, self).__init__(job_type, uni_var)

    def job(self):
        print 'job option 2'
        print uni_var

However, notice that this implementation will require that superClass be changed every time a new subclass is created. Another alternative would be to make the optionFactory method a standalone function (rather than a method of superClass). Like this:

if __name__=='__main__':
    # these variables would normally be called in from a config file
    job_type = 'job1'
    uni_var = 10

    job_select = optionFactory(job_type, uni_var)
    job_select.job()        


class superClass(object):
    def __init__(self, job_type, uni_var):
        self.job_type = job_type   
        self.uni_var = uni_var

    # This is the definition called by the main function it then
    # redirects the request to the appropriate job sub class   
    def job(self):
        raise NotImplementedError()

class option1(superClass):
    def __init__(self, job_type, uni_var):
        super(option1, self).__init__(job_type, uni_var)

    def job(self):
        print 'job option 1'
        print uni_var

class option2(superClass):
    def __init__(self, job_type, uni_var):
        super(option2, self).__init__(job_type, uni_var)

    def job(self):
        print 'job option 2'
        print uni_var

def optionFactory(job_type, uni_var):
    "Return an instance of superClass based on job_type and uni_var."
    if job_type == "job1":
        return option1(job_type, uni_var)
    else:
        return option2(job_type, uni_var)