CODEWITHSUNDEEP
pythonclass
Justin Reid
Justin Reid

Reputation: 119

Instance variables in Python? Keep getting an assignment error

Hi I am trying to write a simple program that calculates the base content of each base in DNA. I keep getting an assignment error 'no_c referenced before assignment' or 'no_c not defined" in my current configuration and I can't figure out how to solve the issue. 

#!/usr/bin/python

#computing the atgc content of a DNA string 


class Base_counter(object):
    def __init__(self, DNA):
        self.DNA = DNA
        no_c = 0
        no_a = 0
        no_g= 0
        no_t= 0

    def c_counter(self):
        for base in self.DNA:   
            if base == 'c':
                no_c = no_c + 1 
        return no_c

    def g_counter(self):
        for base in self.DNA:   
            if base == 'g':
                no_g+=1 
        return no_g

    def a_counter(self):
        for base in self.DNA:   
            if base == 'a':
                no_a+=1 
        return no_a

    def t_counter(self):
        for base in self.DNA:   
            if base == 't':
                no_a+=1 
        return no_t

    def gc_percentage(self):
        return no_c + no_g / len(self.DNA)

    def at_percentage(self):
        return no_a + no_t / len(self.DNA)

    def g_percentage(self):
        return no_g / len(self.DNA)

    def a_percentage(self):
        return no_a / len(self.DNA)

    def t_percentage(self):
        return no_t / len(self.DNA)

    def c_percentage(self):
        return no_c / len(self.DNA)     

def main():
    dna= 'gcgctat'
    analyzer = Base_counter(dna)

    print analyzer.no_c
    print analyzer.c_counter()
    #print analyzer.c_percentage()

if __name__ == '__main__':
    main()

Upvotes: 1

Views: 82

Answers (3)

Steve Barnes
Steve Barnes

Reputation: 28370

Just put self. before all of the no_ values in the class to make them members of each class instance object.

Thus:

class Base_counter(object):
    def __init__(self, DNA):
        self.DNA = DNA
        self.no_c = 0
        self.no_a = 0
        self.no_g= 0
        self.no_t= 0

    def c_counter(self):
        for base in self.DNA:   
            if base == 'c':
                self.no_c += 1 
        return self.no_c

etc.

This is needed so that the instance of a specific class has it's own storage for the values and can reference it.

Upvotes: 0

yerlilbilgin
yerlilbilgin

Reputation: 3409

try this:

    def c_counter(self):
        for base in self.DNA:   
            if base == 'c':
                self.no_c = self.no_c + 1 
        return self.no_c

Specifically, access all fields of the object with the self keyword.

Upvotes: 0

Ami Tavory
Ami Tavory

Reputation: 76297

Consider your code

def __init__(self, DNA):
    self.DNA = DNA
    no_c = 0
    no_a = 0
    no_g= 0
    no_t= 0

Only the line 

    self.DNA = DNA

creates a member for this object. The other lines create mappings that are local to this function. Consequently, when later calls try to access no_c, the interpreter does not connect it to what you presumably meant here.

I'm guessing that you want to replace every occurrence of no_c with self.no_c.

Upvotes: 2

Related Questions