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to Secret Handshake in the Python Track

Published at Jul 13 2018 · 0 comments
Test suite


This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

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".

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:

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):

  • 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.


Bert, in Mary Poppins 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.


import unittest

from secret_handshake import handshake, secret_code

# Tests adapted from `problem-specifications//canonical-data.json` @ v1.2.0

class SecretHandshakeTest(unittest.TestCase):
    def test_wink_for_1(self):
        self.assertEqual(handshake(1), ['wink'])

    def test_double_blink_for_10(self):
        self.assertEqual(handshake(2), ['double blink'])

    def test_close_your_eyes_for_100(self):
        self.assertEqual(handshake(4), ['close your eyes'])

    def test_jump_for_1000(self):
        self.assertEqual(handshake(8), ['jump'])

    def test_combine_two_actions(self):
        self.assertEqual(handshake(3), ['wink', 'double blink'])

    def test_reverse_two_actions(self):
        self.assertEqual(handshake(19), ['double blink', 'wink'])

    def test_reversing_one_action_gives_the_same_action(self):
        self.assertEqual(handshake(24), ['jump'])

    def test_reversing_no_actions_still_gives_no_actions(self):
        self.assertEqual(handshake(16), [])

    def test_all_possible_actions(self):
        self.assertEqual(handshake(15), ['wink',
                                         'double blink',
                                         'close your eyes',

    def test_reverse_all_possible_actions(self):
        self.assertEqual(handshake(31), ['jump',
                                         'close your eyes',
                                         'double blink',

    def test_do_nothing_for_zero(self):
        self.assertEqual(handshake(0), [])

    # Track-specific tests

    def test_code1(self):
        self.assertEqual(secret_code(['close your eyes', 'jump']), 12)

    def test_code2(self):
        self.assertEqual(secret_code(['wink', 'double blink']), 3)

    def test_code3(self):
        self.assertEqual(secret_code(['jump', 'double blink']), 26)

    def test_reversible1(self):
        self.assertEqual(secret_code(handshake(27)), 27)

    def test_reversible2(self):
        self.assertEqual(secret_code(handshake(1)), 1)

    def test_reversible3(self):
        self.assertEqual(secret_code(handshake(7)), 7)

    def test_reversible4(self):
        inp = ['wink', 'double blink', 'jump']
        self.assertEqual(handshake(secret_code(inp)), inp)

if __name__ == '__main__':
import re

class Handshake:

    EVENTS = ['wink', 'double blink', 'close your eyes', 'jump']

    def commands(self, inp):
        if not self.valid_inp(inp):
            return []
        return self.commands_for_num(self.to_num(inp))

    def commands_for_num(self, num):
        if self.testBit(num, 4):
            return list(reversed(self.unreversed_commands(num)))
        return self.unreversed_commands(num)

    def unreversed_commands(self, num):
        return [self.EVENTS[bit] for bit in range(0, 4) if
                self.testBit(num, bit)]

    def code(self, handshake):
        if not self.valid_handshake(handshake):
            return '0'
        return self.code_for_handshake(handshake)

    def code_for_handshake(self, handshake):
        code = self.unreversed_code(handshake)
        if self.EVENTS.index(handshake[0]) > self.EVENTS.index(handshake[-1]):
            # Prepend code with 1 or add 'reverse' bit
            code = self.setBit(code, 4)
        return '{0:b}'.format(code)

    def unreversed_code(self, handshake):
        curr = 0
        for event in handshake:
            curr = self.setBit(curr, self.EVENTS.index(event))
        return curr

    def valid_inp(self, inp):
        if isinstance(inp, int):
            return self.valid_integer(inp)
        elif isinstance(inp, str):
            return self.valid_string(inp)

    def valid_handshake(self, handshake):
        return set(handshake) <= set(self.EVENTS)

    def valid_integer(integer):
        return integer >= 0

    def valid_string(string):
        return not bool(re.search('[^01]', string))

    def testBit(int_type, offset):
        mask = 1 << offset
        return (int_type & mask) > 0

    def setBit(int_type, offset):
        mask = 1 << offset
        return (int_type | mask)

    def to_num(inp):
        if isinstance(inp, str):
            return int(inp, 2)
        return inp

def handshake(num):
    return Handshake().commands(num)

def code(arr):
    return Handshake().code(arr)

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