What is the pythonic way to use multiple constructors for a class?

Question

I am writing some genetic algorithms in python. Currently I was looking at a book that has java code, so but eventually I am trying to write my own Adaptive Genetic algorithm to optimize neural network parameters and layers, and all my neural network code is in python using keras...so I am just writing my own python code that is equivalent to the books java code.

The problem I am having with the way I have it set up currently, is that the constructor always initializes the object to the constructor in the first statement.

From what I have seen from other questions similar to this, you can use classmethods to do this...and you call also do something with ...isinstanceOf method...and you can do something with init method *args and **kwargs...and I thought you could do something with NoneType parameters which is what I am trying to do...but I have been messing with it on and off and cannot seem to get it to work without adding additional boolean arguments which I would prefer not to do.

What are peoples preferred methods to solving the multiple constructor problem, and can you do it the way I am trying to?

An example of where I am trying to use multiple constructors.

class Individual(object):  

#Object Initialisation-->Generally called a constructor
#In python, a variable prefixed with _ is effectively private 
def __init__(self, chromosome, chromosomeLength, bool1):
    if(chromosomeLength is not None and bool1==False):
        self.chromosomeLength = chromosomeLength
        self.fitness = -100
        self.chromosome = np.empty(chromosomeLength)
        for gene in range(self.chromosomeLength):
                if(0.5 < np.random.randint(2)):
                    #self.setGene(gene,1)
                    #cls.chromosome[gene] = 1
                    self.chromosome[gene] = 1
                else:
                    #self.setGene(gene,0)
                    #cls.chromosome[gene] = 0
                    self.chromosome[gene] =0

    elif(chromosome is not None and bool1 ==True):

        self.chromosome = chromosome
        self.fitness = -1
        print ("All variable initialized")

Thanks,

Matt

Post your code as plain text, not an image. See https://stackoverflow.com/help/formatting for code formatting help. — Barmar, Jun 15 '18 at 17:43

score 0 · Answer 1 · answered Jun 15 '18 at 17:43

You could probably use factory functions (or methods, if you like to have them in your class) to construct your objects from different sets of variables:

For instance (pseudocode to illustrate the idea)

from_chromosomes(chromosomes):
    parse_chromosomes
    return Individual(*args, **kwargs)

from_ancestors(parents):
    parse_parents_genes
    return Individual(*args, **kwargs)

(...)

This can be coupled with the use of default values.

What is the pythonic way to use multiple constructors for a class?

1 Answers1