Trying to get ORF’s from a given DNA sequence

I am trying to get a printed output which would be everything from the beginning of the string, to the end, which is until it reaches a certain series of characters like “TAA”, “TAG”, or “TGA”. I can’t get it to work and was wondering if anyone here can help me??

def get_orf(dna):
'''Function should take an argument (string) and find an ORF'''
stopVar = "TAA" or "TGA" or "TAG"
if argument[0:3] == "ATG":
    return
else: 
    return ""
if stopVar in argument:
    return argument[:argument.find(stopVar)]
else:
    return argument
    
return

# Test Cases
#
# You may wish to add more test cases here
argument = 'ATGTGAA'
computed_result = get_orf( argument )
expected_result = 'ATG'
if ( computed_result == expected_result ):
    print ("Test Case 1: Passed")
else:
    print ("Test Case 1: Failed")
    print ("Expected Result:", expected_result)
    print ("Computed Result:", computed_result)

Answer

This works although I am not sure whether you want to return something if the case 'ATG' is found, it is good practice that if one of your returns in a function returns something, then they all should even if it is None:

def get_orf(dna):
    """Function should take an argument (string) and find an ORF."""
    stopVar = "TAA" or "TGA" or "TAG"
    if dna[0:3] == "ATG":
        return "ATG"
    elif stopVar in dna:
        return dna[:dna.find(stopVar)]
    else:
        return dna

# Test Cases
#
# You may wish to add more test cases here
argument = 'ATGTGAA'
computed_result = get_orf(argument)
expected_result = 'ATG'
if (computed_result == expected_result):
    print ("Test Case 1: Passed")
else:
    print ("Test Case 1: Failed")
    print ("Expected Result:", expected_result)
    print ("Computed Result:", computed_result)

With argument = 'ATGTGAA':

Test Case 1: Passed

With argument = 'GATGTGAA':

Test Case 1: Failed
Expected Result: ATG
Computed Result: GATGTGAA

The docstring for functions is with """Text.""" rather then single quotes too so I changed that.