# Secret Handshake > There are 10 types of people in the world: Those who understand > binary, and those who don't. You and your fellow cohort of those in the "know" when it comes to binary decide to come up with a secret "handshake". ```text 1 = wink 10 = double blink 100 = close your eyes 1000 = jump 10000 = Reverse the order of the operations in the secret handshake. ``` Given a decimal number, convert it to the appropriate sequence of events for a secret handshake. Here's a couple of examples: Given the input 3, the function would return the array ["wink", "double blink"] because 3 is 11 in binary. Given the input 19, the function would return the array ["double blink", "wink"] because 19 is 10011 in binary. Notice that the addition of 16 (10000 in binary) has caused the array to be reversed. ## Exception messages Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include a message. To raise a message with an exception, just write it as an argument to the exception type. For example, instead of `raise Exception`, you should write: ```python raise Exception("Meaningful message indicating the source of the error") ``` ## Running the tests To run the tests, run the appropriate command below ([why they are different](https://github.com/pytest-dev/pytest/issues/1629#issue-161422224)): - Python 2.7: `py.test secret_handshake_test.py` - Python 3.4+: `pytest secret_handshake_test.py` Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version): `python -m pytest secret_handshake_test.py` ### Common `pytest` options - `-v` : enable verbose output - `-x` : stop running tests on first failure - `--ff` : run failures from previous test before running other test cases For other options, see `python -m pytest -h` ## Submitting Exercises Note that, when trying to submit an exercise, make sure the solution is in the `$EXERCISM_WORKSPACE/python/secret-handshake` directory. You can find your Exercism workspace by running `exercism debug` and looking for the line that starts with `Workspace`. For more detailed information about running tests, code style and linting, please see the [help page](http://exercism.io/languages/python). ## Source Bert, in Mary Poppins [http://www.imdb.com/title/tt0058331/quotes/qt0437047](http://www.imdb.com/title/tt0058331/quotes/qt0437047) ## Submitting Incomplete Solutions It's possible to submit an incomplete solution so you can see how others have completed the exercise.