Description
Introduction
The goal of this assignment is to get you started writing python functions, and to evaluate your ability to
create high quality efficient code. The work you will be doing in this assignment is not harder than what
you have been doing in exercises up to this point, but this code will be marked by TAs who will evaluate not
only whether your code works, but also whether it is efficient and well designed. Also remember that the
assignments must be completed entirely on your own. So if you get stuck, the TAs can help with general
concepts, but cannot look at your code or help you directly with your implementation. The same goes for
your fellow students. No one should ever look at your assignment code and you should never look at anyone
else’s (until after it’s submitted, at which time you can feel free to share and compare).
What Not to Use
You can complete this assignment using only the material covered in the first four weeks of the course. In
particular, you are not allowed to use loops anywhere in the assignment (there is no good reason to use them
in this assignment!) or any data structures not covered in weeks 1-4.
DNA Sequencing
This assignment deals with DNA sequencing. A DNA sequence is a series of nucleotides: adenine (A),
guanine (G), cytosine (C) and thymine (T). These sequences can be represented as strings of their first
letters. e.g., GCACTAG.
Within these DNA sequences, researchers are interested in finding specific genic sequences (genes). The
input we receive from DNA sequencers usually comes in a continuous stream, so the string may start with
some upstream sequence (data from a previous gene), and may continue beyond the end of the specific gene
that is of interest with a downstream sequence (the start of another gene). Fortunately, all genes start with
the sequence ATG, and the sequence ATG cannot appear in the middle of a gene 1
. This makes it possible to
isolate and analyze a specific gene from a sequence.
Your Tasks
For this assignment, you will be required to build the following 5 functions:
• split input: Takes in a DNA sequence (as described above) and returns a list with three elements, the
upstream data, the gene (if any is found, or an empty string if no gene is found), and the downstream
data, in that order
• get gene: Takes in a DNA sequence (as described above) and returns a string representation of the
gene if one is present, or the string ERROR if no gene is present.
• validate gene: Takes in a string representation of a gene, and returns True iff the gene presented is
valid. For a gene to be valid it must satisfy the following critera:
– It must start with the start codon (3 character sequence) ATG
– It must contain at least one codon after the start codon
– It must contain only full codons (i.e., it cannot end mid-way through a 3 character codon)
– It must never contain four consecutive identical nucleotides
1Note: This isn’t actually true in the real world, but it makes our lives a lot easier, so we’ll pretend
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• is palindromic: Takes a string representation of a gene, and returns True iff that gene is palindromic
(reads the same forwards as backwards).
• evaluate sequence: Takes in a DNA sequence (as described above) and returns one of the following strings as appropriate: {No Gene Found, Invalid Gene, Valid Gene Found, Valid Palindromic
Gene Found}.
Marking
Your assignment will be marked for correctness in a similar manner to your exercises. But it will also be
marked by a TA for elements such as:
• Programming style: Your variable names should be meaningful and your code as simple and clear as
possible.
• Commenting: Your documentation should be clear and concise and allow a user who has not read this
handout to fully understand how to use and manipulate your functions.
• Code re-use: You should have as little duplicated code as possible. If you find yourself repeating code,
there’s a good chance you could find a simpler (lazier) method.
• Testing coverage: Your test cases should not only cover all input categories, but should also be clearly
labelled and organized in a sensible manner.
What to Submit
Submit a0.py and a0.test on MarkUs. Your file must be named exactly as given here (check that MarkUs
says you have submitted all required files after you’re done submitting).
Before you submit:
• Ensure that you have read & added your name and login to the header at the top of the file
• Test your code for PEP-8 compliance
• Run DocTest and make sure you pass all your own cases
• Re-test all examples
Happy Sequencing!
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