darglint 0.4.0

A utility for ensuring Google-style docstringsstay up to date with the source code.

Check out the poster about darglint which was presented at pycon!

A functional docstring linter which checks whether a docstring’s description matches the actual function/method implementation. Darglint expects docstrings to be formatted using the Google Python Style Guide.

Darglint is still in an early stage, and may fail for some things. See the Roadmap section for an idea of where the project is going.

Feel free to submit an issue/pull request if you spot a problem or would like a feature in darglint.

Table of Contents:

• Installation

• Configuration

• Usage

• Sphinx

• Roadmap

• Contribution

Installation

To install darglint, use pip.

pip install darglint

Or, clone the repository, cd to the directory, and

pip install .

Configuration

darglint can be configured using a configuration file. The configuration file must be named either .darglint, setup.cfg, or tox.ini. It must also have a section starting with the section header, [darglint]. Finally, the configuration file must be located either in the directory darglint is called from, or from a parent directory of that working directory.

Currently, the configuration file only allows us to ignore errors and specify message templates. For example, if we would like to ignore ExcessRaiseErrors (because we know that an underlying function will raise an exception), then we would add its error code to a file named .darglint:

[darglint]
ignore=I402

We can ignore multiple errors by using a comma-separated list:

[darglint]
ignore=I402,I103

If we would like to specify a message template, we may do so as follows:

[darglint]
message_template={msg_id}@{path}:{line}

Which will produce a message such as [e-mail]:72.

Finally, we can specify the docstring style type using docstring_style (“google” by default):

[darglint]
docstring_style=sphinx

Usage

Command Line use

Given a python source file, serializers.py, you would check the docstrings as follows:

darglint serializers.py

You can give an optional verbosity setting to darglint. For example,

darglint -v 2 *.py

Would give a description of the error along with information as to this specific instance. The default verbosity is 1, which gives the filename, function name, line number, error code, and some general hints.

To use an arbitrary error format, you can pass a message template, which is a python format string. For example, if we pass the message template

darglint -m "{path}:{line} -> {msg_id}" darglint/driver.py

Then we would get back error messages like

darglint/driver.py :61 -> I101

The following attributes can be passed to the format string: - line: The line number, - msg: The error message, - msg_id: The error code, - obj: The function/method name, - path: The relative file path.

The message template can also be specified in the configuration file as the value message_template.

darglint is particularly useful when combined with the utility, find. This allows us to check all of the files in our project at once. For example, when eating my own dogfood (as I tend to do), I invoke darglint as follows:

find . -name "*.py" | xargs darglint

Where I’m searching all files ending in “.py” recursively from the current directory, and calling darglint on each one in turn.

Ignoring Errors in a Docstring

You can ignore specific errors in a particular docstring. The syntax is much like that of pycodestyle, etc. It generally takes the from of:

# noqa: <error> <argument>

Where <error> is the particular error to ignore (I402, or I201 for example), and <argument> is what (if anything) the ignore statement refers to (if nothing, then it is not specified).

Let us say that we want to ignore a missing return statement in the following docstring:

def we_dont_want_a_returns_section():
  """Return the value, 3.

  # noqa: I201

  """
  return 3

We put the noqa anywhere in the top level of the docstring. However, this won’t work if we are missing something more specific, like a parameter. We may not want to ignore all missing parameters, either, just one particular one. For example, we may be writing a function that takes a class instance as self. (Say, in a bound celery task.) Then we would do something like:

def a_bound_function(self, arg1):
  """Do something interesting.

  Args:
    arg1: The first argument.

  # noqa: I101 arg1

  """
  arg1.execute(self)

So, the argument comes to the right of the error.

We may also want to mark excess documentation as being okay. For example, we may not want to explicitly catch and raise a ZeroDivisionError. We could do the following:

def always_raises_exception(x):
    """Raise a zero division error or type error.o

    Args:
      x: The argument which could be a number or could not be.

    Raises:
      ZeroDivisionError: If x is a number.  # noqa: I402
      TypeError: If x is not a number.  # noqa: I402

    """
    x / 0

So, in this case, the argument for noqa is really all the way to the left. (Or whatever description we are parsing.) We could also have put it on its own line, as # noqa: I402 ZeroDivisionError.

Error Codes

• I101: The docstring is missing a parameter in the definition.

• I102: The docstring contains a parameter not in function.

• I103: The docstring parameter type doesn’t match function.

• I201: The docstring is missing a return from definition.

• I202: The docstring has a return not in definition.

• I203: The docstring parameter type doesn’t match function.

• I301: The docstring is missing a yield present in definition.

• I302: The docstring has a yield not in definition.

• I401: The docstring is missing an exception raised.

• I402: The docstring describes an exception not explicitly raised.

• S001: Describes that something went wrong in parsing the docstring.

• S002: An argument/exception lacks a description.

The error code scheme is based on the errors from the pycodestyle package. The first letter corresponds to the broad class of error:

• I (Interface): Incorrect or incomplete documentation.

• S (Style): Errors with documentation style/syntax.

The number in the hundreds narrows the error by location in the docstring:

• 100: Args section

• 200: Returns section

• 300: Yields section

• 400: Raises section

Sphinx

Darglint can handle sphinx-style docstrings, but imposes some restrictions on top of the Sphinx style. For example, all fields (such as :returns:) must be the last items in the docstring. They must be together, and all indents should be four spaces. These restrictions may be loosened at a later date.

To analyze Sphinx-style docstrings, pass the style flag to the command:

darglint -s sphinx example.py
darglint --docsting-style sphinx example.py

Alternatively, you can specify the style in the configuration file using the setting, “docstring_style”:

[darglint]
docstring_style=sphinx

Roadmap

The below list is the current roadmap for darglint. For each version number, it specifies which features will be added. To see the most recently implemented features, see the CHANGELOG.

0.3

• [x] Take an argument which supports a formatting string for the error message. That way, anyone can specify their own format.

1.0

• [ ] Robust logging for errors caused/encountered by darglint.

• [x] Add support for python versions earlier than 3.6.

• [x] Add more specific line numbers in error messages.

• [ ] Add style errors and suggestions.

• [x] Support for Sphinx-style docstrings.

Other features

I haven’t decided when to add the below features.

• [ ] ALE support.

• [ ] Syntastic support. (Syntastic is not accepting new checkers until their next API stabilizes, so this may take some time.)

• [ ] Check super classes of errors/exceptions raised to allow for more general descriptions in the interface.

Development and Contributions

Development Setup

Install darglint. First, clone the repository:

git clone https://github.com/terrencepreilly/darglint.git

cd into the directory, create a virtual environment (optional), then setup:

cd darglint/
virtualenv -p python3.6 .env
source .env/bin/activate
pip install -e .

You can run the tests using

python setup.py test

Or, install pytest manually, cd to the project’s root directory, and run

pytest

This project tries to conform by the styles imposed by pycodestyle and pydocstyle, as well as by darglint itself.

Contribution

If you would like to tackle an issue or feature, email me or comment on the issue to make sure it isn’t already being worked on. Contributions will be accepted through pull requests. New features should include unit tests, and, of course, properly formatted documentation.