Currency converter

Description

Create a set of functions to convert currency from one denomination to another.

Objectives

Learning Objectives

After completing this assignment, you should understand:

• Test-driven development

Performance Objectives

After completing this assignment, you should be able to:

• Raise exceptions
• Write detailed tests
• Break down programming problems into smaller ones

Details

Deliverables

• A Git repo called currency-converter containing at least:
  • README.md file explaining how to run your project
  • a currency module
  • a test_currency set of tests

Requirements

• Passing unit tests
• No PEP8 or Pyflakes warnings or errors
• No functions longer than 7 lines of code
• 100% test coverage

Normal Mode

Use test-driven development to design a function called convert. Below is a list of all the things it should do. In order to complete this exercise, follow these directions:

• For each requirement, write a test first, and then make the test pass, do not pass Go, do not collect $200.
• Every time you finish a requirement, commit your code with a message describing the requirement.
• Go through the requirements one-by-one. Do not skip around.

Steps:

• Create a function called convert that takes a list called rates, a number called value, a string called from, and a string called to. Make sure than when you call convert with from and to being equal, the return value is the same as value.

• rates list should be a list of tuples, with each tuple containing a currency code you can convert from, a currency code you can convert to, and a rate.

  [("USD", "EUR", 0.74)]

  This means that each dollar is worth 0.74 euros.

  value is the amount of currency, from is the current currency code, and to is the currency code you wish to convert to.

  Given the above rates, make sure that converting 1 dollar into euros returns the following value: 0.74.

• Next, test that you can convert currency with a value that is not 1.

• Next, test that converting 1 euro into dollars returns 1.35 (or an approximation).

• Create a new list of rates with two or more tuples. Make sure you can convert both ways with each rate. For example, with these rates:

  [("USD", "EUR", 0.74), ("EUR", "JPY", 145.949)]

  Make sure you can convert from USD to EUR, EUR to USD, EUR to JPY, and JPY to EUR.

Hard Mode

In addition to the requirements from Normal Mode:

• Make sure that if you try to make a conversion you do not know about, a ValueError is raised with an appropriate message.

• Test that you can convert between any two rates that you have the ability to, even if you do not have a direct conversion rate for them. For example, with the rates:

  [("USD", "EUR", 0.74), ("EUR", "JPY", 145.949)]

  Make sure you can convert from USD to JPY.

  This will probably require Dijkstra's algorithm.

Additional Resources

• Currency charts if you want accurate values.
• The pytest testing framework.
• An Introduction to Test Driven Development.
• Test-Driven Development on Wikibooks.
• Test-Driven Development by Example, the canonical book on this stuff.