Add Resistor Color Expert exercise

resistor-color-expert/.exercism/config.json

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+{
+  "authors": [
+    "meatball133",
+    "bethanyg"
+  ],
+  "files": {
+    "solution": [
+      "resistor_color_expert.py"
+    ],
+    "test": [
+      "resistor_color_expert_test.py"
+    ],
+    "example": [
+      ".meta/example.py"
+    ]
+  },
+  "blurb": "Convert color codes as used on resistors with different bands to a human-readable label.",
+  "source": "Based on earlier resistor color exercises made by Erik Schierboom and Maud de Vries",
+  "source_url": "https://github.com/exercism/problem-specifications/issues/1464"
+}

resistor-color-expert/.exercism/metadata.json

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+{"track":"python","exercise":"resistor-color-expert","id":"f217b52b157b4a4a956ce7f1aad6fe35","url":"https://exercism.org/tracks/python/exercises/resistor-color-expert","handle":"myFirstCode","is_requester":true,"auto_approve":false}

resistor-color-expert/HELP.md

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+# Help
+
+## Running the tests
+
+We use [pytest][pytest: Getting Started Guide] as our website test runner.
+You will need to install `pytest` on your development machine if you want to run tests for the Python track locally.
+You should also install the following `pytest` plugins:
+
+- [pytest-cache][pytest-cache]
+- [pytest-subtests][pytest-subtests]
+
+Extended information can be found in our website [Python testing guide][Python track tests page].
+
+
+### Running Tests
+
+To run the included tests, navigate to the folder where the exercise is stored using `cd` in your terminal (_replace `{exercise-folder-location}` below with your path_).
+Test files usually end in `_test.py`, and are the same tests that run on the website when a solution is uploaded.
+
+Linux/MacOS
+```bash
+$ cd {path/to/exercise-folder-location}
+```
+
+Windows
+```powershell
+PS C:\Users\foobar> cd {path\to\exercise-folder-location}
+```
+
+<br>
+
+Next, run the `pytest` command in your terminal, replacing `{exercise_test.py}` with the name of the test file:
+
+Linux/MacOS
+```bash
+$ python3 -m pytest -o markers=task {exercise_test.py}
+==================== 7 passed in 0.08s ====================
+```
+
+Windows
+```powershell
+PS C:\Users\foobar> py -m pytest -o markers=task {exercise_test.py}
+==================== 7 passed in 0.08s ====================
+```
+
+
+### Common options
+- `-o` : override default `pytest.ini` (_you can use this to avoid marker warnings_)
+- `-v` : enable verbose output.
+- `-x` : stop running tests on first failure.
+- `--ff` : run failures from previous test before running other test cases.
+
+For additional options, use `python3 -m pytest -h` or `py -m pytest -h`.
+
+
+### Fixing warnings
+
+If you do not use `pytest -o markers=task` when invoking `pytest`, you might receive a `PytestUnknownMarkWarning` for tests that use our new syntax:
+
+```bash
+PytestUnknownMarkWarning: Unknown pytest.mark.task - is this a typo?  You can register custom marks to avoid this warning - for details, see https://docs.pytest.org/en/stable/mark.html
+```
+
+To avoid typing `pytest -o markers=task` for every test you run, you can use a `pytest.ini` configuration file.
+We have made one that can be downloaded from the top level of the Python track directory: [pytest.ini][pytest.ini].
+
+You can also create your own `pytest.ini` file with the following content:
+
+```ini
+[pytest]
+markers =
+    task: A concept exercise task.
+```
+
+Placing the `pytest.ini` file in the _root_ or _working_ directory for your Python track exercises will register the marks and stop the warnings.
+More information on pytest marks can be found in the `pytest` documentation on [marking test functions][pytest: marking test functions with attributes] and the `pytest` documentation on [working with custom markers][pytest: working with custom markers].
+
+Information on customizing pytest configurations can be found in the `pytest` documentation on [configuration file formats][pytest: configuration file formats].
+
+
+### Extending your IDE or Code Editor
+
+Many IDEs and code editors have built-in support for using `pytest` and other code quality tools.
+Some community-sourced options can be found on our [Python track tools page][Python track tools page].
+
+[Pytest: Getting Started Guide]: https://docs.pytest.org/en/latest/getting-started.html
+[Python track tools page]: https://exercism.org/docs/tracks/python/tools
+[Python track tests page]: https://exercism.org/docs/tracks/python/tests
+[pytest-cache]:http://pythonhosted.org/pytest-cache/
+[pytest-subtests]:https://github.com/pytest-dev/pytest-subtests
+[pytest.ini]: https://github.com/exercism/python/blob/main/pytest.ini
+[pytest: configuration file formats]: https://docs.pytest.org/en/6.2.x/customize.html#configuration-file-formats
+[pytest: marking test functions with attributes]: https://docs.pytest.org/en/6.2.x/mark.html#raising-errors-on-unknown-marks
+[pytest: working with custom markers]: https://docs.pytest.org/en/6.2.x/example/markers.html#working-with-custom-markers
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit resistor_color_expert.py` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Python track's documentation](https://exercism.org/docs/tracks/python)
+- The [Python track's programming category on the forum](https://forum.exercism.org/c/programming/python)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+Below are some resources for getting help if you run into trouble:
+
+- [The PSF](https://www.python.org) hosts Python downloads, documentation, and community resources.
+- [The Exercism Community on Discord](https://exercism.org/r/discord)
+- [Python Community on Discord](https://pythondiscord.com/) is a very helpful and active community.
+- [/r/learnpython/](https://www.reddit.com/r/learnpython/) is a subreddit designed for Python learners.
+- [#python on Libera.chat](https://www.python.org/community/irc/) this is where the core developers for the language hang out and get work done.
+- [Python Community Forums](https://discuss.python.org/)
+- [Free Code Camp Community Forums](https://forum.freecodecamp.org/)
+- [CodeNewbie Community Help Tag](https://community.codenewbie.org/t/help)
+- [Pythontutor](http://pythontutor.com/) for stepping through small code snippets visually.
+
+Additionally, [StackOverflow](http://stackoverflow.com/questions/tagged/python) is a good spot to search for your problem/question to see if it has been answered already.
+ If not - you can always [ask](https://stackoverflow.com/help/how-to-ask) or [answer](https://stackoverflow.com/help/how-to-answer) someone else's question.

resistor-color-expert/README.md

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+# Resistor Color Expert
+
+Welcome to Resistor Color Expert on Exercism's Python Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Introduction
+
+If you want to build something using a Raspberry Pi, you'll probably use _resistors_.
+Like the previous [`Resistor Color Duo`][resistor-color-duo-exercise] and [`Resistor Color Trio`][resistor-color-trio-exercise] exercises, you will be translating resistor color bands to human-readable labels.
+
+- Each resistor has a resistance value.
+- Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read.
+  To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values.
+- Each band acts as a digit of a number.
+  For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.
+
+
+[resistor-color-duo-exercise]: https://exercism.org/tracks/python/exercises/resistor-color-duo
+[resistor-color-trio-exercise]: https://exercism.org/tracks/python/exercises/resistor-color-trio
+
+## Instructions
+
+In this exercise, you are going to create a helpful program so that you don't have to remember the values of the bands.
+The program will take 1, 4, or 5 colors as input and output the correct value in ohms.
+The color bands are encoded as follows:
+
+- black: 0
+- brown: 1
+- red: 2
+- orange: 3
+- yellow: 4
+- green: 5
+- blue: 6
+- violet: 7
+- grey: 8
+- white: 9
+
+In [`Resistor Color Trio`][resistor-color-trio-exercise] you decoded the first three color bands.
+For instance: orange-orange-brown translated to the main value `330`.
+In this exercise you will need to add _tolerance_ to the mix.
+Tolerance is the maximum amount that a value can be above or below the main value.
+For example, if the last band is green, the maximum tolerance will be `±0.5%`.
+
+The tolerance band will have one of these values:
+
+- grey - 0.05%
+- violet - 0.1%
+- blue - 0.25%
+- green - 0.5%
+- brown - 1%
+- red - 2%
+- gold - 5%
+- silver - 10%
+
+The four-band resistor is built up like this:
+
+| Band_1  | Band_2  | Band_3     | band_4    |
+| ------- | ------- | ---------- | --------- |
+| Value_1 | Value_2 | Multiplier | Tolerance |
+
+Examples:
+
+- orange-orange-brown-green would be `330` ohms with a `±0.5%` tolerance.
+- orange-orange-red-grey would be `3300` ohms with `±0.05%` tolerance.
+
+The difference between a four and five-band resistor is that the five-band resistor has an extra band to indicate a more precise value.
+
+| Band_1  | Band_2  | Band_3  | Band_4     | band_5    |
+| ------- | ------- | ------- | ---------- | --------- |
+| Value_1 | Value_2 | Value_3 | Multiplier | Tolerance |
+
+Examples:
+
+- orange-orange-orange-black-green would be `333` ohms with a `±0.5%` tolerance.
+- orange-red-orange-blue-violet would be `323M` ohms with a `±0.10` tolerance.
+
+There are also one band resistors.
+One band resistors only have the color black with a value of 0.
+
+
+Your program should translate an input `list` of resistor band colors into a label:
+
+"... ohms ...%"
+
+So an input `list` of `["orange", "orange", "black", "green"]` should return:
+
+"33 ohms ±0.5%"
+
+When there are more than a thousand ohms, we say "kiloohms".
+ That's similar to saying "kilometer" for 1000 meters, and "kilograms" for 1000 grams.
+
+So an input `list` of `["orange", "orange", "orange", "grey"]` should return:
+
+"33 kiloohms ±0.05%"
+
+When there are more than a million ohms, we say "megaohms".
+
+So an input `list` of `["orange", "orange", "blue", "red"]` should return:
+
+"33 megaohms ±2%"
+
+[resistor-color-trio-exercise]: https://exercism.org/tracks/python/exercises/resistor-color-trio
+
+## Source
+
+### Created by
+
+- @meatball133
+- @bethanyg
+
+### Based on
+
+Based on earlier resistor color exercises made by Erik Schierboom and Maud de Vries - https://github.com/exercism/problem-specifications/issues/1464

resistor-color-expert/resistor_color_expert.py

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+"""
+Resistor Color Expert.
+
+In this exercise you will need to add tolerance to the mix.
+Tolerance is the maximum amount that a value can be above or
+below the main value. For example, if the last band is green,
+the maximum tolerance will be ±0.5%.
+"""
+
+# Mapping of resistor color names to their corresponding digit values.
+# pylint: disable=R0801
+COLOR_VALUES: dict[str, int] = {
+    "black": 0,
+    "brown": 1,
+    "red": 2,
+    "orange": 3,
+    "yellow": 4,
+    "green": 5,
+    "blue": 6,
+    "violet": 7,
+    "grey": 8,
+    "white": 9,
+}
+
+# Mapping of tolerance band color names to their maximum tolerance suffix.
+MAX_TOLERANCE: dict[str, str] = {
+    "grey": " ±0.05%",
+    "violet": " ±0.1%",
+    "blue": " ±0.25%",
+    "green": " ±0.5%",
+    "brown": " ±1%",
+    "red": " ±2%",
+    "gold": " ±5%",
+    "silver": " ±10%",
+}
+
+
+def resistor_label(colors: list[str]) -> str:
+    """
+    Return a human-readable resistor label from band colors.
+
+    Scales to the largest whole unit (ohms, kiloohms, megaohms, gigaohms)
+    and appends maximum tolerance if present.
+
+    :param colors: Band colors in order. Lengths:
+                   1 (value only);
+                   4 (two digits, multiplier, tolerance);
+                   5 (three digits, multiplier, tolerance).
+    :type colors: list[str]
+    :returns: Scaled value with units and optional tolerance (e.g., '4.7 kiloohms ±5%').
+    :rtype: str
+    :raises KeyError: If an unknown color is provided.
+    """
+    prefix: str = ""
+    postfix: str = ""
+    max_tolerance: str = ""
+
+    if len(colors) == 1:
+        prefix: str = f"{COLOR_VALUES[colors[0]]}"
+
+    if len(colors) == 4:
+        prefix: str = f"{COLOR_VALUES[colors[0]]}{COLOR_VALUES[colors[1]]}"
+        postfix = f"{'0' * COLOR_VALUES[colors[2]]}"
+        max_tolerance = MAX_TOLERANCE[colors[3]]
+
+    if len(colors) == 5:
+        prefix = (
+            f"{COLOR_VALUES[colors[0]]}"
+            f"{COLOR_VALUES[colors[1]]}"
+            f"{COLOR_VALUES[colors[2]]}"
+        )
+        postfix = f"{'0' * COLOR_VALUES[colors[3]]}"
+        max_tolerance = MAX_TOLERANCE[colors[4]]
+
+    int_val: int = int(prefix + postfix)
+
+    # Scale to the largest whole unit
+    # (ohms, kiloohms, megaohms, gigaohms) for readability
+    if 1000 <= int_val < 1000000:
+        return f"{float(int_val / 1000)}".rstrip(".0") + f" kiloohms{max_tolerance}"
+
+    if 1000000 <= int_val < 1000000000:
+        return f"{int_val / 1000000} megaohms{max_tolerance}"
+
+    if 1000000000 <= int_val:
+        return f"{int_val / 1000000000} gigaohms{max_tolerance}"
+
+    return f"{int_val} ohms{max_tolerance}"