OCR Numbers
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 Running the Tests.
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.