# 7. Software Development

This page presents some initial instructions on how to setup your system to start contributing to AequilibraE and lists the requirements for all pull-requests to be merged into master.

## 7.1. Software Design and requirements

The most important piece of AequilibraE’s backend is, without a doubt, numpy.

Whenever vectorization is not possible through the use of NumPy functions, compiled code is developed in order to accelerate computation. All compiled code is written in Cython.

AequilibraE also observes a strong requirement of only using libraries that are available in the Python installation used by QGIS on Windows, as the most important use case of this library is as the computational backend of the AequilibraE GUI for QGIS. This requirement can be relaxed, but it has to be analysed on a base-by-case basis and CANNOT break current workflow within QGIS.

We have not yet found an ideal source of recommendations for developing AequilibraE, but a good initial take can be found in this article.

## 7.2. Development Install

As it goes with most Python packages, we recommend using a dedicated virtual environment to develop AequilibraE.

AequilibraE is currently tested for Python 3.5, 3.6 and 3.7, but we recommend using Python 3.6 for development.

We also assume you are using PyCharm, which is an awesome IDE for Python.

If you are using a different IDE, we would welcome if you could contribute with instructions to set that up.

### 7.2.1. Non-Windows

    ./ci.sh setup_dev

### 7.2.2. Windows

Make sure to clone the AequilibraE repository and run the following from within that cloned repo using an elevated command prompt.

Python 3.6 needs to be installed, and the following instructions assume you are using Chocolatey as a package manager.

    cinst python3 --version 3.6.8
    cinst python

    set PATH=C:\Python36;%PATH%
    python -m pip install pipenv
    virtualenv .venv #Only if you want to save the virtual environment in the same folder
    python -m pipenv install --dev
    python -m pipenv run pre-commit-install

Setup Pycharm with the virtual environment you just created.

    Settings -> Project -> Project Interpreter -> Gear Icon -> Add -> Existing VEnv

## 7.3. Development Guidelines

AequilibraE development (tries) to follow a few standards. Since this is largely an after-the-fact concern, several portions of the code are still not up to such standards.

### 7.3.1. Style

- Python code should follow (mostly) the pycodestyle style guide

- Python docstrings should follow the reStructuredText Docstring Format

- We are big fans of auto-code formatting. For that, we use Black

- Negating some of what we have said so far, we use maximum line length of 120 characters

### 7.3.2. Imports

- Imports should be one per line.

- Imports should be grouped into standard library, third-party, and intra-library imports.

- Imports of NumPy should follow the following convention:

    import numpy as np

### 7.3.3. Contributing to AequilibraE

GitHub has a nice visual explanation on how collaboration is done GitHub Flow. (For us,) The most important points there are:

- The master branch contains the latest working/release version of AequilibraE

- Work is done in an issue/feature branch (or a fork) and then pushed to a new brach

- The test system automatically runs unit tests

- If the tests pass, then a manual pull request can be approved to merge into master

- The master branch is protected and therefore can only be written to after the code has been reviewed and approved

- No individual has the privileges to push to the master branch

### 7.3.4. Release versions

AequilibraE uses the the de-facto Python standard for versioning

    MAJOR.MINOR[.MICRO]

- MAJOR designates a major revision number for the software. Usually, raising a major revision number means that you are adding a lot of features, breaking backward-compatibility or drastically changing the API.

- MINOR usually groups moderate changes to the software like bug fixes or minor improvements. Most of the time, end users can upgrade with no risks their software to a new minor release. In case an API changes, the end users will be notified with deprecation warnings. In other words, API stability is usually a promise between two minor releases.

- Some software use a third level: MICRO. This level is used when the release cycle of minor release is quite long. In that case, micro releases are dedicated to bug fixes.

AequilibraE’s development is happening mostly within the Minor and Micro levels, as we are still in version 0

### 7.3.5. Testing

AequilibraE testing is done with three tools:

- Flake8, a tool to check Python code style

- pytest, a Python testing tool

- coveralls, a tool for measuring test code coverage

To run the tests locally, you will need to figure out what to do…

These same tests are run by Travis with each push to the repository. These tests need to pass in order to somebody manually review the code before merging it into master (or returning for corrections).

In some cases, test targets need to be updated to match the new results produced by the code since these are now the correct results. In order to update the test targets, first determine which tests are failing and then review the failing lines in the source files. These are easy to identify since each test ultimately comes down to one of Python’s various types of assert statements. Once you identify which assert is failing, you can work your way back through the code that creates the test targets in order to update it. After updating the test targets, re-run the tests to confirm the new code passes all the tests.

### 7.3.6. Documentation

All the AequilibraE documentation is (unfortunately) written in reStructuredText and built with Sphinx. Although Restructured Text is often unecessarily convoluted to write, Sphinx is capable of converting it to standard- looking html pages, while also bringing the docstring documentation along for the ride.

To build the documentation, first make sure the required packages are installed. If you have correctly setup the dev environment above, then nothing else is needed. However, if you have incorrectly only run:

    python -m pipenv install

Then you will have to run:

    python -m pipenv install --dev

Next, build the documentation in html format with the following commands run from the `root` folder:

    sphinx-apidoc -T -o docs/source/generated aequilibrae
    cd docs
    make html

### 7.3.7. Releases

AequilibraE releases are manually (and not often) uploaded to the Python Package Index (pypi).

### 7.3.8. Finally

A LOT of the structure around the documentation was borrowed (copied) from the excellent project ActivitySim