0
0
0
0

# helenst's solution

## to Robot Simulator in the Python Track

0
0
0
0
Instructions
Test suite
Solution

Write a robot simulator.

A robot factory's test facility needs a program to verify robot movements.

The robots have three possible movements:

• turn right
• turn left

Robots are placed on a hypothetical infinite grid, facing a particular direction (north, east, south, or west) at a set of {x,y} coordinates, e.g., {3,8}, with coordinates increasing to the north and east.

The robot then receives a number of instructions, at which point the testing facility verifies the robot's new position, and in which direction it is pointing.

• The letter-string "RAALAL" means:
• Turn right
• Turn left
• Turn left yet again
• Say a robot starts at {7, 3} facing north. Then running this stream of instructions should leave it at {9, 4} facing west.

## 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 robot_simulator_test.py`
• Python 3.4+: `pytest robot_simulator_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 robot_simulator_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/robot-simulator` 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.

## Source

Inspired by an interview question at a famous company.

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### robot_simulator_test.py

``````import unittest

from robot_simulator import Robot, NORTH, EAST, SOUTH, WEST

# Tests adapted from `problem-specifications//canonical-data.json` @ v2.2.0

class RobotSimulatorTest(unittest.TestCase):
def test_init(self):
robot = Robot()
self.assertEqual(robot.coordinates, (0, 0))
self.assertEqual(robot.bearing, NORTH)

def test_setup(self):
robot = Robot(SOUTH, -1, 1)
self.assertEqual(robot.coordinates, (-1, 1))
self.assertEqual(robot.bearing, SOUTH)

def test_turn_right(self):
robot = Robot()
for direction in [EAST, SOUTH, WEST, NORTH]:
robot.turn_right()
self.assertEqual(robot.bearing, direction)

def test_turn_left(self):
robot = Robot()
for direction in [WEST, SOUTH, EAST, NORTH]:
robot.turn_left()
self.assertEqual(robot.bearing, direction)

robot = Robot(NORTH, 0, 0)
self.assertEqual(robot.coordinates, (0, 1))
self.assertEqual(robot.bearing, NORTH)

robot = Robot(SOUTH, 0, 0)
self.assertEqual(robot.coordinates, (0, -1))
self.assertEqual(robot.bearing, SOUTH)

robot = Robot(EAST, 0, 0)
self.assertEqual(robot.coordinates, (1, 0))
self.assertEqual(robot.bearing, EAST)

robot = Robot(WEST, 0, 0)
self.assertEqual(robot.coordinates, (-1, 0))
self.assertEqual(robot.bearing, WEST)

def test_simulate_prog1(self):
robot = Robot(NORTH, 0, 0)
robot.simulate("LAAARALA")
self.assertEqual(robot.coordinates, (-4, 1))
self.assertEqual(robot.bearing, WEST)

def test_simulate_prog2(self):
robot = Robot(EAST, 2, -7)
robot.simulate("RRAAAAALA")
self.assertEqual(robot.coordinates, (-3, -8))
self.assertEqual(robot.bearing, SOUTH)

def test_simulate_prog3(self):
robot = Robot(SOUTH, 8, 4)
robot.simulate("LAAARRRALLLL")
self.assertEqual(robot.coordinates, (11, 5))
self.assertEqual(robot.bearing, NORTH)

if __name__ == '__main__':
unittest.main()``````
``````NORTH, EAST, SOUTH, WEST = (0, 1), (1, 0), (0, -1), (-1, 0)

class Robot:
def __init__(self, bearing=NORTH, x=0, y=0):
self._x, self._y = x, y
self._dx, self._dy = bearing

@property
def coordinates(self):
return self._x, self._y

@property
def bearing(self):
return self._dx, self._dy

"""Move forward on current bearing"""
self._x += self._dx
self._y += self._dy

def turn_left(self):
"""Turn left 90 degrees"""
self._dx, self._dy = -self._dy, self._dx

def turn_right(self):
"""Turn right 90 degrees"""
self._dx, self._dy = self._dy, -self._dx

def simulate(self, sequence):
"""Run a sequence of commands"""
commands = {
'L': self.turn_left,
'R': self.turn_right,