# Getting started

## Development dependencies

Working on `cryptography` requires the installation of a small number of development dependencies in addition to the dependencies for Installation. These are listed in `dev-requirements.txt` and they can be installed in a virtualenv using pip. Before you install them, follow the build instructions in Installation (be sure to stop before actually installing `cryptography`). Once you’ve done that, install the development dependencies, and then install `cryptography` in `editable` mode. For example:

    $ # Create a virtualenv and activate it
    $ # Set up your cryptography build environment
    $ pip install --requirement dev-requirements.txt
    $ pip install --editable .

Make sure that `pip install --requirement ...` has installed the Python package `vectors/` and packages on `tests/` . If it didn’t, you may install them manually by using `pip` on each directory.

You will also need to install `enchant` using your system’s package manager to check spelling in the documentation.

Note

There is an upstream bug in `enchant` that prevents its installation on Windows with 64-bit Python. See this Github issue for more information. The easiest workaround is to use 32-bit Python for `cryptography` development, even on 64-bit Windows.

You are now ready to run the tests and build the documentation.

### OpenSSL on macOS

You must have installed OpenSSL via Homebrew or MacPorts and must set `CFLAGS` and `LDFLAGS` environment variables before installing the `dev-requirements.txt` otherwise pip will fail with include errors.

For example, with Homebrew:

    $ env LDFLAGS="-L$(brew --prefix openssl@1.1)/lib" \
        CFLAGS="-I$(brew --prefix openssl@1.1)/include" \
        pip install --requirement ./dev-requirements.txt

Alternatively for a static build you can specify `CRYPTOGRAPHY_SUPPRESS_LINK_FLAGS=1` and ensure `LDFLAGS` points to the absolute path for the OpenSSL libraries before calling pip.

Tip

You will also need to set these values when Building documentation.

## Running tests

`cryptography` unit tests are found in the `tests/` directory and are designed to be run using pytest. pytest will discover the tests automatically, so all you have to do is:

    $ pytest
    ...
    62746 passed in 220.43 seconds

This runs the tests with the default Python interpreter.

You can also verify that the tests pass on other supported Python interpreters. For this we use tox, which will automatically create a virtualenv for each supported Python version and run the tests. For example:

    $ tox
    ...
    ERROR:   pypy: InterpreterNotFound: pypy
     py38: commands succeeded
     docs: commands succeeded
     pep8: commands succeeded

You may not have all the required Python versions installed, in which case you will see one or more `InterpreterNotFound` errors.

## Building documentation

`cryptography` documentation is stored in the `docs/` directory. It is written in reStructured Text and rendered using Sphinx.

Use tox to build the documentation. For example:

    $ tox -e docs
    ...
    docs: commands succeeded
    congratulations :)

The HTML documentation index can now be found at `docs/_build/html/index.html`.