How to write a program in python 2.6 that decodes DNA codons?

[Eric King]

Hello,
My name is Eric and I am using python version 2.6
I am trying to write a program that decodes DNA codons. I have to prompt the user to enter a DNA sequence that is a multiple of 3 and have the program spit out the letters that each 3 letter string represents. Here's an example of what it should look like:
Input a DNA sequence: ACTCTAGCTTTG
---> TLAL
Using the DNA codon table at Wikipedia to find what proteins the 3 letters give. I am very lost on how to do this.
Please help!

[Rabbit]

You could use a loop to loop through the string 3 characters at a time and use a switch to do the translation.

[bvdet]

Create a list of each triplet by iterating on the string "ACTCTAGCTT TG" Hint:

for i in range(0, len(seq), 3)

Define a mapping object (dictionary) to associate each triplet with the corresponding letter.

{"ACT": "T", "CTA": "L", "GCT": "A", "TTG": "L"}

Iterate on the list of triplets, mapping each triplet to the corresponding letter. Join the letters into one string.

"".join([mappedList])

Alternatively, you could concatenate the letters into one string.

>>> result = ""
>>> for letter in ["T", "L", "A", "L"]:
... 	result += letter
... 	
>>> result
'TLAL'
>>>

[Zulhaj Choudhur]

Hello,

I am having difficulty writing the same program. Being new to python and programming, I do not fully understand your post. It would be great if you can give me a more specific example or show me how to start the code. Right now I am assigning each amino acid to a DNA codon and then using an if statement to print the single-leter data-base code. For example:

Isoleucine = ("ATT") , ("ATC") , ("ATA")
Leucine = ("CTT") , ("CTC") , ("CTA") , ("CTG") , ("TTA") , ("TTG")
Valine = ("GTT") , ("GTC") , ("GTA") , ("GTG")
Phenylalanine = ("TTT") , ("TTC")

while True:
    DNA = raw_input("Please enter a DNA sequence in multiples of three:")
    
    if Isoleucine:
        print "I"
    if Leucine: 
        print "L"
    if Valine:
        print "V"
    if Phenylalanine:
        print "F"

here is the result I get

Please enter a DNA sequence in multiples of three:ATT
I
L
V
F
Please enter a DNA sequence in multiples of three:

If someone can guide me in the right direction or tell me how to start that would be great.

[bvdet]

You would begin by defining the dictionary that maps a given triplet to a protein. Example:

tripletDict = {"ATT": "Isoleucine", "CTT": "Leucine"}

The code I posted suggested splitting the input string into parts using slicing. The resulting list of triplets can then be mapped to the proteins in the dictionary in a for loop.

>>> seq = "ATTCTTATT"
>>> [seq[i:i+3] for i in range(0, len(seq), 3)]
['ATT', 'CTT', 'ATT']
>>> for triplet in [seq[i:i+3] for i in range(0, len(seq), 3)]:
... 	print tripletDict[triplet]
... 	
Isoleucine
Leucine
Isoleucine
>>>