String substitution with dictionary - AttributeError: 'NoneType'

[Atalanttore]

Hi,

I'm working on a Exercism programming exercise for transcribing DNA into RNA.

My code looks like this:

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def dna_to_rna(dna_strand):       dna_rna = {'G':'C',                'C':'G',                'T':'A',                'A':'U'}       dna_list = list(dna_strand)     rna_list = []       for dna in dna_list:         rna_list = rna_list.append(dna_rna[dna])     return rna_list   dna_to_rna('ATCGGTTA') # Test function

Unfortunately, this code produces following error and I have no clue why:

1	AttributeError: 'NoneType' object has no attribute 'append'

What's the reason for this 'NoneType' object?

Regards,
Atalanttore

[ThiefOfTime]

The reason for this is that rna_list.append does not return a value. The default for a function returning nothing is None. Since None does not have a function append, you get this error. The function append already appends to the list, there is no return value needed. so just change the line

1	rna_list = rna_list.append(dna_rna[dna])

to

1	rna_list.append(dna_rna[dna])

and it should work just fine :)

[Atalanttore]

Thanks for your explanation. It solved this problem.