CS153 lab1: Introduction to Lab and Rosalind

This is our first lab meeting. Our goals are to introduce the CS lab, to edit a small python program, and to solve a first problem on the Rosalind website. This is just warmup for future homework problems. If there is time, we can also see some other useful lab tools.

If things go smoothly, then you can finish this during our scheduled time. Otherwise, your deadline for this lab is the start of the next lab (10am Monday). A similar rule will apply for most future labs.

YOUR SCRIPT (list of steps)

  1. Login! Sit down at a workstation, and try to login with your Emory NetID and password. If you cannot login, then let us know. If necessary, I'll ask some tech staff to come help us with login issues. You should see a desktop similar to the one on the projector, where I use the "grader account" (cs153001).

    These workstations run Ubuntu Linux, a free operating system that is especially popular in schools and research. It offers both graphical and text-based tools, we'll try some of both.

  2. Find your "Applications" menu, near the top left corner. (You can also get a useful "Activities Overview" by tapping the left "Windows" key, or moving your mouse into the top-left corner). You should be able to find a web browser (Firefox or Chrome), a "Files" browser, and a "Terminal".

  3. Launch a web browser and visit this page:
    You might also bookmark our course homepage, for future reference.

  4. Launch a Terminal.

    A terminal is a text-only "command-line" interface. When it starts, you see a prompt from the shell (the "bash" shell), where you are expected to enter commands. This kind of interface is not friendly to new users, but it can be quite effective once you know some useful commands.

    Enter the following four commands in your terminal. I suggest that you just "copy-and-paste" these lines to your shell (you can paste all four lines at once). I'll demonstrate this on the lab machine.

    I'll assume you have seen files and directories on computers before. Here is what those commands are doing:

    Note your ~/cs153/ should be already created, with some useful privacy settings. In particular, it is readable by the grader account, but not by other students.

    There is much more that we could learn about Linux shell commands, for example see this tutorial. For CS153, we'll just explain such commands as we need them.

  5. Launch the graphical "Files" browser, which usually starts with a view of your "home directory". From there, you can navigate (by double-clicking) into cs153, and then into lab1. You should see an icon for each file that we copied and listed in the previous step. (In fact, we could have copied the files using the file browser.)

  6. One of the files is dna.py, a simple Python program. You can run it already, by entering this command in the terminal: That assumes you are still in the same "current directory" that we set before. If that is not true (maybe you started a new terminal?) then repeat the cd command from above.

    As given, the dna.py program does not do much, but we will start modifying it, and you should be able to finish it.

  7. Open your dna.py in the text editor (gedit). The simplest way is to double-click it in the file browser. Or, you can also start the editor from the terminal with a command: The trailing ampersand (&) tells the shell to run the editor "in the background", so we can enter more shell commands while the editor is still running. (If you forget the ampersand, then quit the editor and try again.)

  8. In the editor, read the dna.py comments for instructions. You are being asked to modify the program so that counts A's, C's, G's, and T's in the given input file. We will do much of this during the lab, so it should not be hard to finish. The last line of your modified dna.py could look like something like this:

  9. Run your modified dna.py program in the terminal, to see if it has reasonable output like "20 12 17 21". If not, go back and fix it until it works. If you get some mysterious error messages, ask for help.

    Once your dna.py is working, we are ready to solve our first problem at Rosalind!

  10. If you have not done so already, go to rosalind.info and setup an account, using your email address. You will need to check your email for an activation message from noreply@rosalind.info. Please enter your full name in your Rosalind profile, so I can tell who you are.

  11. Once your Rosalind account is active, join our class (CS153 Fall 2017) using the "enrollment link" on our homepage. You only need to enroll once. In the future, you can go directly to our Rosalind class page.

  12. At our Rosalind class page, click the first problem, "Counting DNA Nucleotides". Read it. It asks us to solve the problem that we just solved using dna.py, so we are ready to solve it!

  13. If you are using Firefox, I recommend that you first configure it to "always asks me where to save files". Look for "Preferences" under the "hamburger menu", and it should be under the first page of "General" preferences. If you forget to do this, Firefox by default saves all file downloads in a fixed location (directory ~/Downloads/).
  14. Now back on the Rosalind DNA problem page, click the big blue "Download Dataset" button. A 5-minute timer starts. You are downloading a text file called rosalind_dna.txt. I recommend that you save it in ~/cs153/lab1/, overwriting our original file with the same name.

  15. Now back in the terminal, run dna.py again: Assuming the output (a single line with four integers) looks good, you should copy-and-paste that line to the Rosalind window, in the textbox labeled "Copy your answer here:". Next, use the second "Choose File" button to select your python program (~/cs153/lab1/dna.py). Finally, hit the big blue "Submit" button.

  16. If you do not finish within the five-minute time limit, no problem. Just figure out how to do it a bit faster, and try again. Rosalind has no limit on retries (but it may give you a different input file each time).

  17. Rosalind will let you know whether your submission was correct. Try again until you get it.

  18. Once you are done at Rosalind, there is one other thing to check. Make sure you have left a working copy of dna.py in your ~/cs153/lab1/ directory. Once you have done those two things, you are done with today's lab. You may leave early, if you want, or try some of the other (non-credit) Rosalind problems.

    Note you do not have to finish this during our lab time, our actual duedate for this lab is the start of the next lab (10am Monday). But if you are doing this away from the lab, the hardest part may be getting a copy of your program back into the your "~/cs153/lab1" directory. (It can be done remotely, but that requires some software tools.)

    Today we just wanted to get the basic tools and Rosalind working. The code today is so simple that I am not enforcing an "honor statement". We will be more strict about future programs.