# Contributing Guidelines

## Before Contributing

Welcome to [TheAlgorithms/Python](https://github.com/TheAlgorithms/Python)! Before submitting your pull requests, please ensure that you __read the entire guidelines__. If you have any doubts about the contributing guide, please feel free to [state them clearly in an issue](https://github.com/TheAlgorithms/Python/issues/new) or ask the community on [Gitter](https://gitter.im/TheAlgorithms/community).

## Contributing

### Contributor

We are delighted that you are considering implementing algorithms and data structures for others! This repository is referenced and used by learners from all over the globe. By being one of our contributors, you agree and confirm that:

- You did your work — no plagiarism allowed.
  - Any plagiarized work will not be merged.
- Your work will be distributed under the [MIT License](LICENSE.md) once your pull request is merged.
- Your submitted work fulfills or mostly fulfills our styles and standards.

__New implementations__ are welcome! For example, new solutions for a problem, different representations for a graph data structure, or algorithm designs with different complexities. However, __identical implementations__ of an existing one are not allowed. Please check whether the solution is already implemented before submitting your pull request.

__Improving comments__ and __writing proper tests__ are also highly welcome.

### Contribution

We appreciate any contribution — from fixing a grammar mistake in a comment to implementing complex algorithms. Please read this section if you are contributing your work.

Your contribution will be tested by our [automated testing on GitHub Actions](https://github.com/TheAlgorithms/Python/actions) to save time and mental energy. After you have submitted your pull request, you should see the GitHub Actions tests start to run at the bottom of your submission page.

If those tests fail, then click on the ___details___ button to read through the GitHub Actions output to understand the failure. If you do not understand, please leave a comment on your submission page, and a community member will try to help.

#### Issues

If you are interested in resolving an [open issue](https://github.com/TheAlgorithms/Python/issues), simply make a pull request with your proposed fix. __We do not assign issues in this repo__, so please do not ask for permission to work on an issue.

__Do not__ create an issue to contribute an algorithm. Please submit a pull request instead.

Please help us keep our issue list small by adding `Fixes #{$ISSUE_NUMBER}` to the description of pull requests that resolve open issues.
For example, if your pull request fixes issue #10, then please add the following to its description:

```text
Fixes #10
```

GitHub will use this tag to [auto-close the issue](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue) if and when the PR is merged.

#### What is an Algorithm?

An algorithm is one or more functions (or classes) that:

- take one or more inputs,
- perform some internal calculations or data manipulations,
- return one or more outputs,
- have minimal side effects (e.g., `print()`, `plot()`, `read()`, `write()`).

Algorithms should be packaged in a way that would make it easy for readers to integrate them into larger programs.

Algorithms should:

- have intuitive class and function names that make their purpose clear to readers,
- use Python naming conventions and intuitive variable names to ease comprehension,
- be flexible to take different input values,
- have Python type hints for their input parameters and return values,
- raise Python exceptions (`ValueError`, etc.) on erroneous input values,
- have docstrings with clear explanations and/or URLs to source materials,
- contain doctests that test both valid and erroneous input values,
- return all calculation results instead of printing or plotting them.

Algorithms in this repo should not be simple how-to examples for existing Python packages. Instead, they should perform internal calculations or manipulations to convert input values into different output values.
These calculations or manipulations can use data types, classes, or functions of existing Python packages, but each algorithm in this repo should add unique value.

#### Pre-Commit Plugin

- have intuitive class and function names that make their purpose clear to readers
- use Python naming conventions and intuitive variable names to ease comprehension
- be flexible to take different input values
- have Python type hints for their input parameters and return values
- raise Python exceptions (`ValueError`, etc.) on erroneous input values
- have docstrings with clear explanations and/or URLs to source materials
- contain doctests that test both valid and erroneous input values
- return all calculation results instead of printing or plotting them

Algorithms in this repo should not be how-to examples for existing Python packages. Instead, they should perform internal calculations or manipulations to convert input values into different output values.
Those calculations or manipulations can use data types, classes, or functions of existing Python packages, but each algorithm in this repo should add unique value.

#### Pre-commit

Use [pre-commit](https://pre-commit.com/#installation) to automatically format your code to match our coding style:

```bash
python3 -m pip install pre-commit  # only required the first time
pre-commit install
```

That's it! Pre-commit will run every time you commit any changes. If any errors are found during the run, fix them and commit those changes. You can even run the plugin manually on all files:

```bash
pre-commit run --all-files --show-diff-on-failure
```

#### Coding Style

We want your work to be readable by others; therefore, we encourage you to note the following:

- Please write in free-threaded Python 3.15t+. For instance: `print()` is a function in Python 3, so `print "Hello"` will *not* work, but `print("Hello")` will.

- Please focus hard on the naming of functions, classes, and variables. Help your reader by using __descriptive names__ that can help you to remove redundant comments.
  - Single-letter variable names are *old school*, so please avoid them unless their life only spans a few lines.
  - Expand acronyms because `gcd()` is hard to understand but `greatest_common_divisor()` is not.
  - Please follow the [Python Naming Conventions](https://pep8.org/#prescriptive-naming-conventions) so variable_names and function_names should be lower_case, CONSTANTS in UPPERCASE, ClassNames should be CamelCase, etc.

- We encourage the use of Python [f-strings](https://realpython.com/python-f-strings/#f-strings-a-new-and-improved-way-to-format-strings-in-python) where they make the code easier to read.

- Please consider running [__ruff format__](https://docs.astral.sh/ruff/formatter/) on your Python file(s) before submitting your pull request. This is not yet a requirement, but it does make your code more readable and automatically aligns it with much of [PEP 8](https://peps.python.org/pep-0008/). To use it,

  ```bash
  python3 -m pip install ruff  # only required the first time
  ruff format
  ```

- All submissions will need to pass the test `ruff check` before they will be accepted, so if possible, try this test locally on your Python file(s) before submitting your pull request.

  ```bash
  python3 -m pip install ruff  # only required the first time
  ruff check
  ```

- Original code submissions require docstrings or comments to describe your work.

- More on docstrings and comments:

  If you used a Wikipedia article or other source material to create your algorithm, please add the URL in a docstring or comment to help your reader.

  The following are considered to be bad and may be requested to be improved:

  ```python
  x += 2  # increased by 2
  ```

  This is too trivial. Comments should not merely repeat what the code already says. Comments should explain ___why___ we are doing things. Comments on the same line as code should never cause the line to wrap (> 88 characters per line).
Comments which are not on the same line as code should appear ___before___ the code they describe. "First tell the reader ___why___ with comments and then show them ___how___ with code."

  We require you to put docstrings inside your functions, but please pay attention to the indentation of docstrings. The following is a good example:

  ```python
  def sum_ab(a, b):
      """
      Return the sum of two integers a and b.
      """
      return a + b
  ```

- Write tests (especially [__doctests__](https://docs.python.org/3/library/doctest.html)) to illustrate and verify your work. We highly encourage the use of *doctests on all functions*.

  ```python
  def sum_ab(a, b):
      """
      Return the sum of two integers a and b
      >>> sum_ab(2, 2)
      4
      >>> sum_ab(-2, 3)
      1
      >>> sum_ab(4.9, 5.1)
      10.0
      """
      return a + b
  ```

  These doctests will be run by pytest as part of our automated testing, so please try to run your doctests locally and make sure that they are found and pass:

  ```bash
  python3 -m doctest -v my_submission.py
  ```

  The use of the Python built-in `input()` function is __not__ encouraged:

  ```python
  input("Enter your input:")
  # Or even worse...
  input = eval(input("Enter your input: "))
  ```

  However, if your code uses `input()` then we encourage you to gracefully deal with leading and trailing whitespace in user input by adding `.strip()` as in:

  ```python
  starting_value = int(input("Please enter a starting value: ").strip())
  ```

  The use of [Python type hints](https://docs.python.org/3/library/typing.html) is encouraged for function parameters and return values. Our CI runs [ty](https://docs.astral.sh/ty/) as an informational check that does not block merges yet, so you may want to run it locally before making your submission.

  ```bash
  python3 -m pip install ty  # only required the first time
  ty check my_file_path.py
  ```

  ```python
  def sum_ab(a: int, b: int) -> int:
      return a + b
  ```

  [Install ty](https://docs.astral.sh/ty/installation/) and then please use the command `ty check` to test all files or `ty check path/to/file.py` to test a specific file.

- [__List comprehensions and generators__](https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions) are preferred over the use of `lambda`, `map`, `filter`, `reduce` but the important thing is to demonstrate the power of Python in code that is easy to read and maintain.

- Avoid importing external libraries for basic algorithms. Only use those libraries for complicated algorithms.

- If you need a third-party module that is not already listed in __pyproject.toml__, please add it to the `dependencies` there as part of your submission. The `uv-lock` pre-commit hook will update `uv.lock` to match.

#### Other Requirements for Submissions

- If you are submitting code in the `project_euler/` directory, please also read [the dedicated Guideline](https://github.com/TheAlgorithms/Python/blob/master/project_euler/README.md) before contributing to our Project Euler library.
- The file extension for code files should be `.py`. Jupyter Notebooks should be submitted to [TheAlgorithms/Jupyter](https://github.com/TheAlgorithms/Jupyter).
- Strictly use snake_case (underscore_separated) in your file_name, as it will be easy to parse in the future using scripts.
- Please avoid creating new directories if at all possible. Try to fit your work into the existing directory structure.
- If possible, follow the standard *within* the folder you are submitting to.
- If you have modified/added code, make sure the code compiles before submitting.
- If you have modified/added documentation work, ensure your language is concise and contains no grammar errors.
- Do not update the README.md or DIRECTORY.md file, which will be periodically autogenerated by our GitHub Actions processes.
- Add a corresponding explanation to [Algorithms-Explanation](https://github.com/TheAlgorithms/Algorithms-Explanation) (Optional but recommended).
- Our CI runs [__ty__](https://docs.astral.sh/ty/) on every pull request as an informational check that does not block merges yet, so we encourage you to add [__Python type hints__](https://docs.python.org/3/library/typing.html) where `ty` recommends to do so.
- Most importantly,
  - __Be consistent in the use of these guidelines when submitting.__
  - __Join__ us on [Discord](https://discord.com/invite/c7MnfGFGa6) and [Gitter](https://gitter.im/TheAlgorithms/community) __now!__
  - Happy coding!

Writer [@poyea](https://github.com/poyea), Jun 2019.