Python classes that create each others' class objects [duplicate]

Question

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Help with Python UnboundLocalError: local variable referenced before assignment

In python3, I have two classes, one for DNA and one for RNA. I would like the DNA class to have a method that takes the DNA sequence (an instance variable of DNA, self.sequence), changes it into an RNA sequence (easily done with a for loop), and then creates an RNA object with the new sequence as an instance variable.

At the same time, I would like the RNA class to have a method that does the opposite (That is, it takes the RNA sequence, produces a corresponding DNA sequence, and then creates a DNA object that uses the sequence as an instance variable.)

My method for making RNA from DNA is as follows:

def transcribe(self):
    RNAseq=''
    for base in self.sequence:
        if base=='A' or base=='C' or base=='G':
            RNAseq=RNAseq+base
        if base=='T':
            RNAseq=RNAseq+'U'
    RNA=RNA(RNAseq,self.name+'RNA')
    return RNA

This code gives me the error: UnboundLocalError: local variable 'RNA' referenced before assignment

Can what I want to do be done?

Is RNA the name of your RNA class?

BrenBarn
– BrenBarn

2012-12-07 07:00:31 +00:00
Commented Dec 7, 2012 at 7:00 — BrenBarn
– BrenBarn, Commented Dec 7, 2012 at 7:00

NPE · Accepted Answer · 2012-12-07 07:01:53Z

5

Call your variable something other than RNA, e.g. rna:

rna = RNA(RNAseq, self.name + 'RNA')
return rna

Otherwise you're trying to use the same name for two different things, the class and the variable, and the latter shadows the former.

answered Dec 7, 2012 at 7:01

NPE

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2 Comments

user1884604 Over a year ago

That worked great, thanks! I feel a little silly now, but lesson learned!

NPE Over a year ago

@user1884604: No need to feel silly. That error message isn't terribly clear.

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