ledger exercise entry class

python/ledger/README.md

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+# Ledger
+
+Refactor a ledger printer.
+
+The ledger exercise is a refactoring exercise. There is code that prints a
+nicely formatted ledger, given a locale (American or Dutch) and a currency (US
+dollar or euro). The code however is rather badly written, though (somewhat
+surprisingly) it consistently passes the test suite.
+
+Rewrite this code. Remember that in refactoring the trick is to make small steps
+that keep the tests passing. That way you can always quickly go back to a
+working version.  Version control tools like git can help here as well.
+
+Please keep a log of what changes you've made and make a comment on the exercise
+containing that log, this will help reviewers.
+
+## 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 ledger_test.py`
+- Python 3.4+: `pytest ledger_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 ledger_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/ledger` 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](http://exercism.io/tracks/python/tests).
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.