Usage¤

Writing duties¤

Your tasks, or duties, are defined in a Python module. By default, duty will load these tasks from a duties.py file at the root of your repository.

Each task is declared as a "duty", using the duty.duty decorator.

from duty import duty


@duty
def docs(ctx):
    ctx.run("mkdocs build", title="Building documentation")

The ctx argument is the "context" of the duty. It is automatically created and passed to your function.

It has only one purpose: running command with its run method. The run method accepts strings, list of strings, or even Python callables.

The above duty runs the command in a shell process. To avoid using a shell, pass a list of strings instead:

from duty import duty


@duty
def docs(ctx):
    ctx.run(["mkdocs", "build"], title="Building documentation")
    # avoid the overhead of an extra shell process

And to avoid using a subprocess completely, pass a Python callable:

from duty import duty
from mkdocs import build, config


@duty
def docs(ctx):
    ctx.run(build.build, args=[config.load_config()], title="Building documentation")
    # avoid the overhead of an extra Python process

For convenience, duty provides callables for many popular Python tools, so that you don't have to read their source and learn how to call them. For example, the mkdocs build command can be called like this:

from duty import duty
from duty.callables import mkdocs


@duty
def docs(ctx):
    ctx.run(mkdocs.build, kwargs={"strict": True}, title="Building documentation")

Lazy callables¤

Not only imports to third-party modules are deferred when our callables run, but the callables themselves are lazy, meaning you can call them directly, without passing arguments and keyword arguments with the args and kwargs parameters of ctx.run():

from duty import duty
from duty.callables import mkdocs


@duty
def docs(ctx):
    ctx.run(mkdocs.build(strict=True), title="Building documentation")

The main benefit is that it enables IDE features like help tooltips and auto-completion, as well as improving readability and writability.

See all our callables in the Code reference.

You can also create your own lazy callables with duty.tools.Tool and duty.tools.lazy. Check out our tools to see how to create your own.

The lazy function/decorator is a quicker way to create a lazy callable:

from duty import duty, tools

from griffe.cli import check


@duty
def check_api(ctx):
    griffe_check = tools.lazy(check, name="griffe.check")
    ctx.run(griffe_check("pkg"))

ctx.run() options¤

The run methods accepts various options, mostly coming from its underlying dependency: failprint.

Arguments of the run method:

Example usage of the silent option:

@duty
def clean(ctx):
    ctx.run("find . -type d -name __pycache__ | xargs rm -rf", silent=True)

Default options¤

Let's say you have more than one command, and you want to silence all of them. Instead of passing silent=True to all ctx.run() calls, you can set this option as default in the decorator itself:

@duty(silent=True)
def clean(ctx):
    ctx.run("rm -rf .coverage*")
    ctx.run("rm -rf .mypy_cache")
    ctx.run("rm -rf .pytest_cache")
    ctx.run("rm -rf build")
    ctx.run("rm -rf dist")
    ctx.run("rm -rf pip-wheel-metadata")
    ctx.run("rm -rf site")
    ctx.run("find . -type d -name __pycache__ | xargs rm -rf")
    ctx.run("find . -name '*.rej' -delete")

You can of course override the default options in the ctx.run() calls:

@duty(capture=True)
def run_scripts(ctx):
    ctx.run("bash script1.sh")
    ctx.run("bash script2.sh")
    ctx.run("bash script3.sh", capture=False)

Options as a context manager¤

You can temporarily change options for several run calls with ctx.options():

@duty
def run_scripts(ctx):
    with ctx.options(nofail=True):
        ctx.run("bash script1.sh")
        ctx.run("bash script2.sh")
    ctx.run("bash script3.sh")

Such temporary changes will stack above the previous ones each time you enter the with clause, and unstack each time you leave it:

@duty
def run_scripts(ctx):
    ctx.run("bash script0.sh")  # defaults

    with ctx.options(nofail=True):
        ctx.run("bash script1.sh")  # nofail=True

        with ctx.options(quiet=True):
            ctx.run("bash script2.sh")  # nofail=True, quiet=True

            with ctx.options(silent=True, nofail=False):
                ctx.run("bash script3.sh")  # nofail=False, quiet=True, silent=True

            ctx.run("bash script4.sh")  # nofail=True, quiet=True

        ctx.run("bash script5.sh")  # nofail=True

    ctx.run("bash script6.sh")  # defaults

Changing the working directory¤

You can change the working directory for a specific run:

@duty
def run_scripts(ctx):
    ctx.run("bash script3.sh", workdir="subfolder")

Or for a group of run calls, using the options context manager:

@duty
def run_scripts(ctx):
    ctx.run("echo in .")
    ctx.run("ls")
    with ctx.options(workdir="subfolder"):
        ctx.run("echo in subfolder")
        ctx.run("ls")

@duty
def run_scripts(ctx):
    ctx.run("echo in .")  # run in ./
    with ctx.options(workdir="A"):
        ctx.run("echo in A")  # run in ./A
        with ctx.options(workdir="B"):
            ctx.run("echo in...")  # run in ./B, not ./A/B!

@duty
def run_scripts(ctx):
    ctx.run("echo in .")  # run in ./
    with ctx.options(workdir="A"):
        ctx.run("echo in A")  # run in ./A
        l = os.listdir()  # run in ./, not ./A!

Another way to change the working directory is to use the ctx.cd(directory) context manager:

@duty
def run_scripts(ctx):
    ctx.run("echo in .")  # run in ./

    with ctx.cd("A"):
        ctx.run("echo in A")  # run in ./A
        l = os.listdir()  # run in ./A as well

        with ctx.cd("B"):
            ctx.run("echo in A/B")  # run in ./A/B
            ctx.run("echo in A/B/C", workdir="C")  # run in ./A/B/C

        ctx.run("echo in A")  # back to ./A

    ctx.run("echo in .")  # back to ./

Saving the output of a command¤

In duty 0.7 (thanks to failprint 0.8), the run method of the context objects always returns the captured output of the command (even when it also prints it on the standard output). If nothing was captured, the returned output will be empty.

You can therefore use ctx.run as a shortcut to get the output of a command.

Before duty 0.7:

import subprocess

from duty import duty


@duty
def action(ctx):
    requirements = subprocess.run(
        ["pip", "freeze"],
        stdout=subprocess.PIPE,
        stderr=subprocess.STDOUT,
        text=True,
    ).output
    ...

With duty 0.7:

from duty import duty


@duty
def action(ctx):
    requirements = ctx.run(["pip", "freeze"])
    ...

Passing standard input to a command¤

failprint 0.8 introduced the ability to pass text as standard input to a command. duty 0.7 takes advantage of this new failprint version, and therefore allows you to do the same in your duties.

Before duty 0.7, to pass standard input to a command, you had to write a shell command, for example:

@duty
def check_dependencies(ctx):
    ctx.run(
        "pdm export -f requirements --without-hashes | safety check --stdin --full-report",
        title="Checking dependencies",
    )

This had a few issues:

• you had to use a shell command, which brings its lot of platform-and-shell-dependent issues, such as:
  • shell might not be the same everywhere
  • on Windows, there were high chances the safety executable would not be found

To fix the latter, you had to compute the absolute paths of all exectuables in the command before-hand (except the first one, which failprint handles itself):

@duty
def check_dependencies(ctx):
    safety = which("safety") or "safety"  # hope for the best
    ctx.run(
        f"pdm export -f requirements --without-hashes | {safety} check --stdin --full-report",
        title="Checking dependencies",
        pty=PTY,
    )

With duty 0.7, everything is easier and more robust since you can save the output of a command in a variable, and then pass this variable as standard input to another command! This allows to write commands as lists of strings (better cross-platform support, less resource-consuming), and reuse the output of one command as input of several others:

@duty
def check_dependencies(ctx):
    requirements = ctx.run(
        ["pdm", "export", "-f", "requirements", "--without-hashes"],
        title="Exporting dependencies as requirements",
        allow_overrides=False,
        # this is a preparation command that must not be altered
        # by CLI options targetted at the next commands,
        # see "Preventing options overrides"
    )
    ctx.run(
        ["safety", "check", "--stdin", "--full-report"],
        title="Checking dependencies",
        stdin=requirements,
    )
    ctx.run(
        ["other", "command", "using", "requirements"],
        title="Checking one more thing",
        stdin=requirements,
    )

Pre/post duties¤

Each duty can be configured to run other duties before or after itself, with the pre and post decorator options.

The pre and post options accept a list of other duties to run. These other duties can be passed directly, or can be looked up using their names. You can also pass any callable that accepts a context argument, just like any duty.

For example, you can create a composite duty check that calls other, more specific checking duties:

# looking up duties thanks to their names, allowing to reference duties
# that have not yet been declared in the collection
@duty(pre=["check_quality", "check_types", "check_docs", "check_dependencies"])
def check(ctx):
    """Check it all!"""

Or you can make sure to always run the clean duty before running your tests, and print a coverage report after running them:

@duty
def clean(ctx):
    ctx.run("rm -rf tests/tmp")


@duty
def coverage(ctx):
    ctx.run("coverage combine", nofail=True)
    ctx.run("coverage report", capture=False)


@duty(pre=[clean], post=[coverage])
def test(ctx):
    ctx.run("pytest tests")

@duty(nofail=True, capture=False)
def coverage(ctx):
    ctx.run("coverage combine")
    ctx.run("coverage report")


@duty(post=[lambda ctx: coverage.run()])
def test(ctx):
    ctx.run("pytest tests")

Defining aliases¤

Duties can have aliases. By default, duty will create an alias for each duty by replacing underscores with dashes. It means that, even if you duty is called check_docs, you can call it with duty check-docs on the command line, or reference it using check-docs in pre/post duties.

If you wish to add more aliases to a duty (for example to provide shorter names), use the decorator aliases option:

@duty(aliases=["start", "up"])
def start_backend(ctx):
    ctx.run("docker-compose up")

With this example, you'll be able to start the backend with any of the four equivalent commands:

duty start_backend
duty start-backend
duty start
duty up

Skipping duties¤

You can tell duty to always skip a duty if a certain condition is met. This feature is inspired by pytest's skip_if marker.

@duty(
    skip_if=sys.version_info < (3, 8),
    skip_reason="Building docs is not supported on Python 3.7",
)
def docs(ctx):
    ctx.run("mkdocs build")

By default, skip_reason will be "duty: skipped" where "duty" is replaced by the name of the duty.

Listing duties¤

Once you have defined some duties, you can list them from the CLI with the -l, --list option. Example:

$ duty --list
  changelog             Update the changelog in-place with latest commits.
  check                 Check it all!
  check-api             Check for API breaking changes.
  check-dependencies    Check for vulnerabilities in dependencies.
  check-docs            Check if the documentation builds correctly.
  check-quality         Check the code quality.
  check-types           Check that the code is correctly typed.
  clean                 Delete temporary files.
  cov                   Report coverage as text and HTML.
  docs                  Serve the documentation (localhost:8000).
  docs-deploy           Deploy the documentation on GitHub pages.
  format                Run formatting tools on the code.
  release               Release a new Python package.
  test                  Run the test suite.

You can also show help for given duties with the -h, --help option:

$ duty --help release
usage: duty release [-c {stdout,stderr,both,none}] [-f {pretty,tap}] [-y | -Y] [-p | -P] [-q | -Q] [-s | -S] [-z | -Z]

Release a new Python package.

Parameters:
    ctx: The context instance (passed automatically).
    version: The new version number to use.

options:
  -c {stdout,stderr,both,none}, --capture {stdout,stderr,both,none}
                        Which output to capture. Colors are supported with 'both' only, unless the command has a 'force color' option.
  -f {pretty,tap}, --fmt {pretty,tap}, --format {pretty,tap}
                        Output format. Pass your own Jinja2 template as a string with '-f custom=TEMPLATE'. Available variables: command, title (command or title passed with -t), code (exit
                        status), success (boolean), failure (boolean), number (command number passed with -n), output (command output), nofail (boolean), quiet (boolean), silent (boolean).
                        Available filters: indent (textwrap.indent).
  -y, --pty             Enable the use of a pseudo-terminal. PTY doesn't allow programs to use standard input.
  -Y, --no-pty          Disable the use of a pseudo-terminal. PTY doesn't allow programs to use standard input.
  -p, --progress        Print progress while running a command.
  -P, --no-progress     Don't print progress while running a command.
  -q, --quiet           Don't print the command output, even if it failed.
  -Q, --no-quiet        Print the command output when it fails.
  -s, --silent          Don't print anything.
  -S, --no-silent       Print output as usual.
  -z, --zero, --nofail  Don't fail. Always return a success (0) exit code.
  -Z, --no-zero, --strict
                        Return the original exit code.

It prints the docstring of the corresponding function as well as all the duty options you can use (same options for every duties).

Running duties¤

To run a duty, simply use:

duty clean

If you are using Poetry or PDM:

poetry run duty clean
pdm run duty clean

You can pass multiple duties in one command:

duty clean docs

Passing parameters¤

Duties can accept arguments (or parameters):

@duty
def docs(ctx, serve: bool = False):
    command = "serve" if serve else "build"
    ctx.run(f"mkdocs {command}")

When passing the argument from the command line, it will be type-casted using the parameter annotation in the duty's signature. If there is no annotation but a default value, it will be type-casted using the type of the default value.

We support any type that is callable and accepts one positional argument (a string), as well as optional types (Optional[...], ... | None) and union types (Union[..., ...], ... | ...).

The bool type uses a special conversion table:

To pass a parameter as a keyword argument, use the name=value form:

duty docs serve=yes  # --> serve = True

You can use your own custom types as well:

class Point:
    def __init__(self, xy: str):
        self.x, self.y = xy.split(",")


@duty
def shoot(ctx, point: Point):
    ctx.run(f"shoot -x {point.x} -y {point.y}")

Then, when running the duty:

duty shoot point=5,15

You can also pass parameters as positional arguments:

duty shoot 5,15

If your duty accepts variadic positional arguments, those can be passed too from the command line:

@duty
def shout(ctx, *names):
    ctx.run(print, args=[f"{name.upper()}!" for name in names])

duty shout herbert marvin

This can also be used to pass additional CLI flags to commands or duty tools. If the flags clash with duty's own options, add -- first:

from duty import duty, tools

@duty
def docs(ctx, *cli_args) -> None:
    ctx.run(tools.mkdocs.serve().add_args(*cli_args), capture=False)

duty docs -- -vs -f mkdocs.yml

Passing options¤

Usage summary:

duty [GLOBAL_OPTS...] [DUTY [DUTY_OPTS...] [DUTY_PARAMS...]...]

Global options¤

The duty command line tool accepts global options that will affect all the duties selected to run. These options are the same you can use in ctx.run() calls, except for number and title (because it wouldn't make sense).

The specified global options will override the default options of duties, as well as the options passed in ctx.run() calls!

For example, with a duty declaring these options:

@duty(capture="both")
def play(ctx, file):
    ctx.run(f"play {file}", nofail=True)

...you can override both the capture and nofail options like this:

duty --capture=none --strict play this-file.mp4
# or with the short options
duty -Zc none play this-file.mp4 

Local options¤

Local options are the same as global options. Instead of passing them to duty directly, you can pass them to a specific duty on the command line. If we use the previous example again:

duty play -Zc none this-file.mp4 

It allows to use different options for different duties selected on the command line. In the following example, the format and check duties will have their output captured, while the test duty will not:

duty -cboth format check test -cnone

Preventing options overrides from the CLI¤

If for some reason you would like to prevent the ability to override an option with the command line global or local options, pass allow_overrides=False to your ctx.run() call, or even to your ctx.options() context manager:

@duty
def run_scripts(ctx):
    # no option can be changed from the CLI for the following run
    ctx.run("bash script1.sh", quiet=False, allow_overrides=False)

    # not for these runs either
    with ctx.options(nofail=True, allow_overrides=False):
        ctx.run("bash script2.sh")
        ctx.run("bash script3.sh")

Capturing commands output¤

When running a command through ctx.run(), you can choose to capture its standard output, its standard error, both, or none.

Captured output is then available as an output variable when formatting duty's output.

• capture=stdout will capture both stdout and stderr, but will only make stdout available while formatting
• capture=stderr will capture both stdout and stderr, but will only make stderr available while formatting
• capture=both will capture both stdout and stderr as one single stream, and will make it available while formatting
• capture=none will not capture anything, and both stdout and stderr will be printed in real-time to the console

It is not possible to capture only stdout, or only stderr, and let the other one be printed to the console. Capturing one is capturing both, but discarding the other.

Formatting duty output¤

Thanks to its underlying failprint dependency, it is possible to change the output of command runs. The output of a command is rendered using a Jinja template string. For example, the two builtin failprint formats are:

• pretty (default)

  {% if success %}<green>✓</green>
  {% elif nofail %}<yellow>✗</yellow>
  {% else %}<red>✗</red>{% endif %} 
  <bold>{{ title or command }}</bold>
  {% if failure %} ({{ code }}){% endif %}
  {% if failure and output and not quiet %}\n
  {{ ('  > ' + command + '\n') if title else '' }}
  {{ output|indent(2 * ' ') }}{% endif %}
  

  Its "progress" template is > {{ title or command }}.

• tap

  {% if failure %}not {% endif %}ok {{ number }} - {{ title or command }}
  {% if failure and output %}\n  ---
  \n  {{ ('command: ' + command + '\n  ') if title else '' }}
  output: |\n{{ output|indent(4 * ' ') }}\n  ...{% endif %}
  

As you can see there are variables you can use in your format template:

There is also one Jinja filter available

To select a different format than the default one, or to provide your own, you can use the fmt option of ctx.run(), the --format CLI option (global and local), and the FAILPRINT_FORMAT environment variable.

For example, here is how to use the tap format:

# in the ctx.run() call
@duty
def task1(ctx):
    ctx.run("echo failed && false", fmt="tap")


# or as a default duty option
@duty(fmt="tap")
def task2(ctx):
    ctx.run("echo failed && false")
    ctx.run("echo failed && false")

# or with the CLI global option
duty --format tap task1 task2

# or with a CLI local option
duty task1 -ftap task2

# or with an environment variable
FAILPRINT_FORMAT=tap duty task1 task2

To use your own format template, just make the value of the fmt option start with custom=. For example, with an environment variable:

export FAILPRINT_FORMAT="custom={{output}}"
# always print the captured output, nothing else

duty task1 task2