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to OCR Numbers in the Python Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Note:

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.

Given a 3 x 4 grid of pipes, underscores, and spaces, determine which number is represented, or whether it is garbled.

Step One

To begin with, convert a simple binary font to a string containing 0 or 1.

The binary font uses pipes and underscores, four rows high and three columns wide.

     _   #
    | |  # zero.
    |_|  #
         # the fourth row is always blank

Is converted to "0"

         #
      |  # one.
      |  #
         # (blank fourth row)

Is converted to "1"

If the input is the correct size, but not recognizable, your program should return '?'

If the input is the incorrect size, your program should return an error.

Step Two

Update your program to recognize multi-character binary strings, replacing garbled numbers with ?

Step Three

Update your program to recognize all numbers 0 through 9, both individually and as part of a larger string.

 _ 
 _|
|_ 
   

Is converted to "2"

      _  _     _  _  _  _  _  _  #
    | _| _||_||_ |_   ||_||_|| | # decimal numbers.
    ||_  _|  | _||_|  ||_| _||_| #
                                 # fourth line is always blank

Is converted to "1234567890"

Step Four

Update your program to handle multiple numbers, one per line. When converting several lines, join the lines with commas.

    _  _ 
  | _| _|
  ||_  _|
         
    _  _ 
|_||_ |_ 
  | _||_|
         
 _  _  _ 
  ||_||_|
  ||_| _|
         

Is converted to "123,456,789"

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 ocr_numbers_test.py
  • Python 3.4+: pytest ocr_numbers_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 ocr_numbers_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/ocr-numbers 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 the Bank OCR kata http://codingdojo.org/cgi-bin/wiki.pl?KataBankOCR

Submitting Incomplete Solutions

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

ocr_numbers_test.py

"""Tests for the ocr-numbers exercise

Implementation note:
ocr.convert should validate its input and
raise ValueErrors with meaningful error messages
if necessary.
"""

import unittest

from ocr_numbers import convert


# Tests adapted from `problem-specifications//canonical-data.json` @ v1.1.0

class OcrNumbersTest(unittest.TestCase):
    def test_recognizes_0(self):
        self.assertEqual(convert([" _ ",
                                  "| |",
                                  "|_|",
                                  "   "]), '0')

    def test_recognizes_1(self):
        self.assertEqual(convert(["   ",
                                  "  |",
                                  "  |",
                                  "   "]), '1')

    def test_unreadable(self):
        self.assertEqual(convert(["   ",
                                  "  _",
                                  "  |",
                                  "   "]), '?')

    def test_line_number_not_multiple_of_four(self):
        with self.assertRaisesWithMessage(ValueError):
            convert([" _ ",
                     "| |",
                     "   "])

    def test_col_number_not_multiple_of_three(self):
        with self.assertRaisesWithMessage(ValueError):
            convert(["    ",
                     "   |",
                     "   |",
                     "    "])

    def test_recognizes_110101100(self):
        input_grid = [
            "       _     _        _  _ ",
            "  |  || |  || |  |  || || |",
            "  |  ||_|  ||_|  |  ||_||_|",
            "                           "
        ]
        self.assertEqual(convert(input_grid), "110101100")

    def test_garbled_numbers_in_string(self):
        input_grid = [
            "       _     _           _ ",
            "  |  || |  || |     || || |",
            "  |  | _|  ||_|  |  ||_||_|",
            "                           "
        ]
        self.assertEqual(convert(input_grid), "11?10?1?0")

    def test_recognizes_2(self):
        self.assertEqual(convert([" _ ",
                                  " _|",
                                  "|_ ",
                                  "   "]), "2")

    def test_recognizes_3(self):
        self.assertEqual(convert([" _ ",
                                  " _|",
                                  " _|",
                                  "   "]), "3")

    def test_recognizes_4(self):
        self.assertEqual(convert(["   ",
                                  "|_|",
                                  "  |",
                                  "   "]), "4")

    def test_recognizes_5(self):
        self.assertEqual(convert([" _ ",
                                  "|_ ",
                                  " _|",
                                  "   "]), "5")

    def test_recognizes_6(self):
        self.assertEqual(convert([" _ ",
                                  "|_ ",
                                  "|_|",
                                  "   "]), "6")

    def test_recognizes_7(self):
        self.assertEqual(convert([" _ ",
                                  "  |",
                                  "  |",
                                  "   "]), "7")

    def test_recognizes_8(self):
        self.assertEqual(convert([" _ ",
                                  "|_|",
                                  "|_|",
                                  "   "]), "8")

    def test_recognizes_9(self):
        self.assertEqual(convert([" _ ",
                                  "|_|",
                                  " _|",
                                  "   "]), "9")

    def test_recognizes_string_of_decimal_numbers(self):
        input_grid = [
            "    _  _     _  _  _  _  _  _ ",
            "  | _| _||_||_ |_   ||_||_|| |",
            "  ||_  _|  | _||_|  ||_| _||_|",
            "                              "
        ]
        self.assertEqual(convert(input_grid), "1234567890")

    def test_recognizes_numbers_separated_by_empty_lines(self):
        input_grid = [
            "    _  _ ",
            "  | _| _|",
            "  ||_  _|",
            "         ",
            "    _  _ ",
            "|_||_ |_ ",
            "  | _||_|",
            "         ",
            " _  _  _ ",
            "  ||_||_|",
            "  ||_| _|",
            "         "
        ]
        self.assertEqual(convert(input_grid), "123,456,789")

    # Utility functions
    def setUp(self):
        try:
            self.assertRaisesRegex
        except AttributeError:
            self.assertRaisesRegex = self.assertRaisesRegexp

    def assertRaisesWithMessage(self, exception):
        return self.assertRaisesRegex(exception, r".+")


if __name__ == '__main__':
    unittest.main()
class Ocr:

    NUM_ROWS = 4
    NUM_COLS = 3
    UNRECOGNIZED_NUM = "?"
    GRID_NUMS = {"0": [" _ ", "| |", "|_|", "   "],
                 "1": ["   ", "  |", "  |", "   "],
                 "2": [" _ ", " _|", "|_ ", "   "],
                 "3": [" _ ", " _|", " _|", "   "],
                 "4": ["   ", "|_|", "  |", "   "],
                 "5": [" _ ", "|_ ", " _|", "   "],
                 "6": [" _ ", "|_ ", "|_|", "   "],
                 "7": [" _ ", "  |", "  |", "   "],
                 "8": [" _ ", "|_|", "|_|", "   "],
                 "9": [" _ ", "|_|", " _|", "   "]}

    NUMS = {"".join(value): key for key, value in GRID_NUMS.items()}

    @classmethod
    def numbers(cls, inp):
        return "".join(map(cls.number, zip(*map(cls.split_every_three, inp))))

    @classmethod
    def grids(cls, inp):
        return map("".join, zip(*map(cls.grid, inp)))

    @classmethod
    def number(cls, inp):
        if not cls.valid_num(inp):
            raise ValueError
        return cls.NUMS.get("".join(inp), cls.UNRECOGNIZED_NUM)

    @classmethod
    def grid(cls, inp):
        if not cls.valid_grid(inp):
            raise ValueError
        return cls.GRID_NUMS.get(inp)

    @classmethod
    def valid_num(cls, inp):
        return (all(len(row) == cls.NUM_COLS for row in inp) and
                len(inp) == cls.NUM_ROWS)

    @classmethod
    def valid_grid(cls, inp):
        return all(char in cls.GRID_NUMS.keys() for char in inp)

    @classmethod
    def split_every_three(cls, inp):
        return cls.split(inp, 3)

    @staticmethod
    def split(inp, size):
        return [inp[start:start + size] for start in range(0, len(inp), size)]


def number(inp):
    return Ocr.numbers(inp)


def grid(inp):
    return Ocr.grids(inp)

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