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to Ledger in the Python Track

Published at Aug 17 2020 · 0 comments
Instructions
Test suite
Solution

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:

raise Exception("Meaningful message indicating the source of the error")

Running the tests

To run the tests, run pytest ledger_test.py

Alternatively, you can tell Python to run the pytest module: 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.

Submitting Incomplete Solutions

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

ledger_test.py

# -*- coding: utf-8 -*-
import unittest

from ledger import format_entries, create_entry


class LedgerTest(unittest.TestCase):
    maxDiff = 5000

    def test_empty_ledger(self):
        currency = 'USD'
        locale = 'en_US'
        entries = []
        expected = 'Date       | Description               | Change       '
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_one_entry(self):
        currency = 'USD'
        locale = 'en_US'
        entries = [
            create_entry('2015-01-01', 'Buy present', -1000),
        ]
        expected = '\n'.join([
            'Date       | Description               | Change       ',
            '01/01/2015 | Buy present               |      ($10.00)',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_credit_and_debit(self):
        currency = 'USD'
        locale = 'en_US'
        entries = [
            create_entry('2015-01-02', 'Get present', 1000),
            create_entry('2015-01-01', 'Buy present', -1000),
        ]
        expected = '\n'.join([
            'Date       | Description               | Change       ',
            '01/01/2015 | Buy present               |      ($10.00)',
            '01/02/2015 | Get present               |       $10.00 ',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_multiple_entries_on_same_date_ordered_by_description(self):
        currency = 'USD'
        locale = 'en_US'
        entries = [
            create_entry('2015-01-02', 'Get present', 1000),
            create_entry('2015-01-01', 'Buy present', -1000),
        ]
        expected = '\n'.join([
            'Date       | Description               | Change       ',
            '01/01/2015 | Buy present               |      ($10.00)',
            '01/02/2015 | Get present               |       $10.00 ',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_final_order_tie_breaker_is_change(self):
        currency = 'USD'
        locale = 'en_US'
        entries = [
            create_entry('2015-01-01', 'Something', 0),
            create_entry('2015-01-01', 'Something', -1),
            create_entry('2015-01-01', 'Something', 1),
        ]
        expected = '\n'.join([
            'Date       | Description               | Change       ',
            '01/01/2015 | Something                 |       ($0.01)',
            '01/01/2015 | Something                 |        $0.00 ',
            '01/01/2015 | Something                 |        $0.01 ',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_overlong_description(self):
        currency = 'USD'
        locale = 'en_US'
        entries = [
            create_entry('2015-01-01', 'Freude schoner Gotterfunken', -123456),
        ]
        expected = '\n'.join([
            'Date       | Description               | Change       ',
            '01/01/2015 | Freude schoner Gotterf... |   ($1,234.56)',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_euros(self):
        currency = 'EUR'
        locale = 'en_US'
        entries = [
            create_entry('2015-01-01', 'Buy present', -1000),
        ]
        expected = '\n'.join([
            'Date       | Description               | Change       ',
            u'01/01/2015 | Buy present               |      (€10.00)',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_dutch_locale(self):
        currency = 'USD'
        locale = 'nl_NL'
        entries = [
            create_entry('2015-03-12', 'Buy present', 123456),
        ]
        expected = '\n'.join([
            'Datum      | Omschrijving              | Verandering  ',
            '12-03-2015 | Buy present               |   $ 1.234,56 ',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_dutch_locale_and_euros(self):
        currency = 'EUR'
        locale = 'nl_NL'
        entries = [
            create_entry('2015-03-12', 'Buy present', 123456),
        ]
        expected = '\n'.join([
            'Datum      | Omschrijving              | Verandering  ',
            u'12-03-2015 | Buy present               |   € 1.234,56 ',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_dutch_negative_number_with_3_digits_before_decimal_point(self):
        currency = 'USD'
        locale = 'nl_NL'
        entries = [
            create_entry('2015-03-12', 'Buy present', -12345),
        ]
        expected = '\n'.join([
            'Datum      | Omschrijving              | Verandering  ',
            '12-03-2015 | Buy present               |    $ -123,45 ',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)

    def test_american_negative_number_with_3_digits_before_decimal_point(self):
        currency = 'USD'
        locale = 'en_US'
        entries = [
            create_entry('2015-03-12', 'Buy present', -12345),
        ]
        expected = '\n'.join([
            'Date       | Description               | Change       ',
            '03/12/2015 | Buy present               |     ($123.45)',
        ])
        self.assertEqual(format_entries(currency, locale, entries), expected)


if __name__ == '__main__':
    unittest.main()
# -*- coding: utf-8 -*-
from datetime import datetime
from babel.numbers import format_decimal

TABLE_FORMAT = "{:<10} | {:<25} | {:<13}"
LOCALES = {
    "en_US": {
        "date": "Date",
        "change": "Change",
        "description": "Description",
        "change_func": lambda currency, change: format_change_us(currency, change),
        "date_format": "%m/%d/%Y",
    },
    "nl_NL": {
        "date": "Datum",
        "change": "Verandering",
        "description": "Omschrijving",
        "change_func": lambda currency, change: format_change_nl(currency, change),
        "date_format": "%d-%m-%Y",
    },
}
CURRENCIES = {"USD": "$", "EUR": "€"}


class LedgerEntry:
    def __init__(self):
        self.date = None
        self.description = None
        self.change = None

    def format_date(self, date_format):
        return self.date.strftime(date_format)


class LedgerTable:
    def __init__(self, locale, currency, table_format, entries):
        self.locale = locale
        self.currency = currency
        self.table_format = table_format
        self.entries = entries

    def format_date(self, entry):
        return entry.format_date(self.locale["date_format"])

    def calculate_change(self, entry):
        return self.locale["change_func"](self.currency, entry.change)

    def format(self):
        return "\n".join(
            [
                TABLE_FORMAT.format(
                    self.locale["date"],
                    self.locale["description"],
                    self.locale["change"],
                )
            ]
            + [
                TABLE_FORMAT.format(
                    self.format_date(entry),
                    truncate_string(entry.description, 25),
                    self.calculate_change(entry),
                )
                for entry in self.entries
            ]
        )


def create_entry(date, description, change):
    entry = LedgerEntry()
    entry.date = datetime.strptime(date, "%Y-%m-%d")
    entry.description = description
    entry.change = change
    return entry


def format_entries(currency, locale, entries):
    table = build_table(currency, locale, entries)
    return table.format()


def build_table(currency, locale, entries):
    entries.sort(key=lambda entry: (entry.date, entry.change))
    return LedgerTable(
        LOCALES[locale],
        entries=entries,
        currency=CURRENCIES[currency],
        table_format=TABLE_FORMAT,
    )


def truncate_string(string, length):
    if len(string) > length:
        truncated_length = length - 3
        return f"{string[:truncated_length]}..."
    return string


def format_change_us(currency, change):
    change_str = f"{currency}{(abs(change) / 100):,.2f}"
    if change < 0:
        change_str = f"({change_str})"
    else:
        change_str = f"{change_str} "
    return f"{change_str :>13}"


def format_change_nl(currency, change):
    change_str = f'{currency} {format_decimal(change / 100, locale = "nl_NL")} '
    return f"{change_str:>13}"

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