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to Ledger in the Python Track

Published at Apr 09 2021 · 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 functools import total_ordering
from math import copysign


@total_ordering
class LedgerEntry:
    def __init__(self, date, description, change):
        self.date = datetime.strptime(date, '%Y-%m-%d')
        self.description = description
        self.change = change

    def __le__(self, other):
        return (self.date, self.description, self.change) < (other.date, other.description, other.change)

    def __eq__(self, other):
        return (self.date, self.description, self.change) == (other.date, other.description, other.change)


create_entry = LedgerEntry


#
# Currencies
#

class Currency:
    _currencies = {}

    currency: str = None
    symbol: str = None
    sub_unit_len = 2

    def __init_subclass__(cls, **kwargs):
        super().__init_subclass__(**kwargs)
        assert cls.currency and cls.currency not in Currency._currencies
        Currency._currencies[cls.currency] = cls

    @staticmethod
    def get_currency(name):
        return Currency._currencies[name]


class Euro(Currency):
    currency = 'EUR'
    symbol = '€'


class USDollar(Currency):
    currency = 'USD'
    symbol = '$'


#
# Locales
#

class Locale:
    _locales = {}

    locale: str = None
    headers: dict = None
    date_format: str = None
    currency_formats: dict = None
    decimal_separator: str = None
    thousand_separator: str = None

    def __init_subclass__(cls, **kwargs):
        super().__init_subclass__(**kwargs)
        assert cls.locale and cls.locale not in Locale._locales
        Locale._locales[cls.locale] = cls

    @staticmethod
    def get_locale(name):
        return Locale._locales[name]

    @classmethod
    def format_currency(cls, value, currency):
        sign = int(copysign(1, value))
        value = abs(value)

        sub_unit_value = value % 10 ** currency.sub_unit_len
        unit_value = value // 10 ** currency.sub_unit_len

        sub_units = str(sub_unit_value).zfill(currency.sub_unit_len)
        units = f'{unit_value:_}'.replace('_', cls.thousand_separator)

        formatted_value = f'{units}{cls.decimal_separator}{sub_units}'
        return cls.currency_formats[sign].format(currency=currency.symbol, value=formatted_value)


class LocaleEnUs(Locale):
    locale = 'en_US'
    date_format = '%m/%d/%Y'
    headers = {
        'date': 'Date',
        'description': 'Description',
        'change': 'Change',
    }
    decimal_separator = '.'
    thousand_separator = ','
    currency_formats = {
        1: '{currency}{value} ',
        -1: '({currency}{value})'
    }


class LocaleNlNl(Locale):
    locale = 'nl_NL'
    date_format = '%d-%m-%Y'
    headers = {
        'date': 'Datum',
        'description': 'Omschrijving',
        'change': 'Verandering',
    }
    decimal_separator = ','
    thousand_separator = '.'
    currency_formats = {
        1: '{currency} {value} ',
        -1: '{currency} -{value} '
    }


#
# Formatter
#

def format_entries(currency, locale, entries):
    if isinstance(currency, str):
        currency = Currency.get_currency(currency)
    if isinstance(locale, str):
        locale = Locale.get_locale(locale)

    date_width = 10
    desc_width = 25
    chng_width = 13

    date = locale.headers['date']
    description = locale.headers['description']
    change = locale.headers['change']

    table = [
        f'{date:<{date_width}} | {description:<{desc_width}} | {change:<{chng_width}}'
    ]

    for entry in sorted(entries):
        date = entry.date.strftime(locale.date_format)
        description = entry.description
        change = locale.format_currency(value=entry.change, currency=currency)

        # Trim the description
        if len(description) > desc_width:
            description = description[:desc_width-3] + '...'

        table.append(
            f'{date:<{date_width}} | {description:<{desc_width}} | {change:>{chng_width}}'
        )

    return '\n'.join(table)

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