iotaa

It's One Thing After Another

A simple workflow engine with semantics inspired by Luigi and tasks expressed as decorated Python functions (or methods, but "functions" will be used in this document). iotaa is pure Python, relies on no third-party packages, and is contained in a single module.

Workflows

Workflows comprise:

• Assets (observable external state: typically files, but more abstract entities -- a count of lines in a file, a REST API response, a time of day -- can be modeled)
• Requirement relationships (dependencies) between assets
• Executable logic to ready the assets (e.g. create them)

Assets

An asset (an instance of class iotaa.Asset) has two attributes:

1. ref: A value, of any type, uniquely identifying the observable state this asset represents (e.g. a POSIX filesystem path, an S3 URI, an ISO8601 timestamp)
2. ready: A 0-arity (no-argument) function returning a bool indicating whether the asset is "ready", i.e. safe to use by a requiring task

Assets are created by calling iotaa.asset().

Tasks

Task are functions that declare, by yielding values to iotaa, the task name and -- depending on task type -- one or both of: the task's asset(s), and any other task(s) the task requires. The task name is used to construct log messages detailing workflow progress, so descriptive names can be useful. Tasks that define and are responsible for readying their asset(s) provide, following the yield statements, executable logic that does whatever is needed to ready the asset(s).

iotaa provides three Python decorators to define tasks:

@task

The essential workflow function type, a @task function yields, in order:

1. Its name
2. An asset -- or an asset list, or a dict mapping str keys to assets, or None -- the task is responsible for readying
3. A task-function call (e.g. t(args) for task t) -- or a list or dict of such calls, or None -- the task requires before it can ready its asset(s)

Arbitrary Python statements may appear before and interspersed between the yield statements. If all assets of any required tasks are ready, the statements following the third and final yield will be executed, with the expectation that they will ready this task's asset(s).

@tasks

A collections of other tasks. A @tasks function is ready when all of its required tasks are ready and yields, in order:

1. Its name
2. A task-function call (e.g. t(args) for task t) -- or a list or dict of such calls, or None -- that this task requires.

No statements should follow the second and final yield, as they will never execute.

@external

An @external function represents zero or more required assets that cannot be readied by the workflow and yields, in order:

1. Its name
2. A required asset -- or an asset list, or a dict mapping str keys to assets, or None -- that must be readied by external means not under workflow control.

As with @task functions, arbitrary Python statements may appear before and interspersed between these yield statements. However, no statements should follow the second and final yield, as they will never execute.

Use

Installation

Installation via a conda package at anaconda.org:

• Into an existing, activated conda environment: conda install -c conda-forge iotaa
• Into a new environment called iotaa: conda create -n iotaa -c conda-forge iotaa

Installation via a pip package at pypi.org:

• Into an existing, activated venv environment: pip install iotaa

Installation via local source, from the src/ directory of an iotaa git clone:

• Into an existing, activated venv environment: pip install .
• Into an arbitrary directory (e.g. directory to be added to PYTHONPATH, or path to a venv): pip install --prefix /some/path .

Integration into another package:

• Copy the src/iotaa/__init__.py module as iotaa.py to another project. No iotaa CLI program will be available in this case, but iotaa.main() can be used to create one.

CLI Use

% iotaa --help
usage: iotaa [-d] [-h] [-g] [-t] [-v] module [function] [args ...]

positional arguments:
  module
    application module name or path
  function
    task name
  args
    task arguments

optional arguments:
  -d, --dry-run
    run in dry-run mode
  -h, --help
    show help and exit
  -g, --graph
    emit Graphviz dot to stdout
  -t, --tasks
    show available tasks
  -v, --verbose
    enable verbose logging

Specifying positional arguments m f hello 88 would call task function f in module m with arguments hello: str and 88: int. Positional arguments args are parsed with the json library into Python values. To support intra-run idempotence (i.e. multiple tasks may depend on the same task, but the latter will only be evaluated/executed once), JSON values parsed to Python dict objects will be converted to a hashable (and therefore cacheable) dict subtype, and list objects will be converted to tuples. Both should be treated as read-only in iotaa application code.

It is assumed that m is importable by Python by any customary means. However, if m is a valid absolute or relative path (and so more likely specified as m.py or /path/to/m.py), its parent directory is automatically added by iotaa to sys.path so that it can be loaded.

A task tree of arbitrary complexity defined in module m may be entered at any point by specifying the appropriate task function f. Only f and its children will be processed, resulting in partial execution of a potentially larger workflow graph.

The function argument is optional (and ignored) if the -t / --tasks option, which lists the names of task functions in module, is specified.

Programmatic Use

After installation, import iotaa or from iotaa import ... to access public members. See the demo application below for example use.

Dry-Run Mode

Use the CLI --dry-mode switch (or call dryrun() programmatically) to run iotaa in a mode where no post-yield statements in @task bodies are executed. When applications are written such that no state-changing statements precede the final yield statement, dry-run mode will report the current condition of the workflow, identifying not-ready requirements that are blocking workflow progress.

Helpers

A number of public helper functions are available in the iotaa module:

Function	Description
asset()	Instantiates an asset to return from a task function.
dryrun()	Activates dry-run mode.
graph()	Returns a Graphviz representation of the most recent task execution tree.
logcfg()	Configures Python's root logger to support logging.info() (et al.) calls, which iotaa itself makes. It is called by the iotaa CLI, but is available for standalone applications with simple logging needs to call programmatically.
logset()	Accepts a Python Logger object and configures iotaa to send all future log messages to it.
main()	The entry-point function for CLI use.
refs()	Accepts the value returned by a decorated task function and returns ref values of the assets in the same structure as returned by the function.
run()	Runs a command in a subshell.
runconda()	Runs a command in a subshell with a named conda environment activated.
tasknames()	Accepts an object (e.g. a module) and returns a list of names of iotaa task members. This function is called when the -t / --tasks argument is provided to the CLI, which then prints each task name followed by, when available, the first line of its docstring.

Development

In the base environment of a conda installation (Miniforge recommended), install the condev package, then run make devshell in the root of an iotaa git clone. See the condev docs for details but, in short: In the development shell created by make devshell, one may edit and test code live (either by starting a python REPL, or by invoking the iotaa CLI program), run the auto-formatter with make format, and run the code-quality tests with make test. Type exit to exit the development shell. (The underlying DEV-iotaa conda environment created by make devshell will persist until manually removed, so future make devshell invocations should be much faster than the first one, which had to create the environment.)

Notes

• Workflows can be invoked repeatedly, potentially making further progress with each invocation, depending on readiness of external requirements. Since task functions' assets are checked for readiness before their requirements are checked or their post-yield statements are executed, completed work is never performed twice -- unless the asset becomes not-ready via external means. For example, one might notice that an asset is incorrect, remove it, fix the workflow code, then re-run the workflow; iotaa would perform whatever work is necessary to re-ready the asset, but nothing more.
• A task may be instantiated in statements before the statement yielding it to iotaa, but note that control will pass to it immediately. For example, a task might have, instead of the statement yield foo(x), the separate statements foo_assets = foo(x) (first) and yield foo_assets (later). In this case, control would be passed to foo (and potentially to a tree of tasks it requires) immediately upon evaluation of the expression foo(x). This should be fine semantically, but be aware of the order of execution it implies.
• For its dry-run mode to work correctly, iotaa assumes that no statements that change external state execute before the final yield statement in a task function's body.
• Currently, iotaa is single-threaded, so it truly is "one thing after another". Concurrent execution of mutually independent tasks may be added in future work.

Demo

Consider the source code of the demo application, which simulates making a cup of tea (according to the official recipe).

The first @tasks method defines the end result: A cup of tea, steeped, with sugar -- and a spoon to stir in the sugar:

@tasks
def a_cup_of_tea(basedir):
    # A cup of steeped tea with sugar, and a spoon.
    yield "The perfect cup of tea"
    yield [spoon(basedir), steeped_tea_with_sugar(basedir)]

As described above, a @tasks function must yield its name and the assets it requires: In this case, the steeped tea with sugar, and a spoon. Since this function is a @tasks connection, no executable statements follow the final yield.

The spoon() and cup() @task functions are straightforward:

@task
def spoon(basedir):
    # A spoon to stir the tea.
    path = Path(basedir) / "spoon"
    yield "A spoon"
    yield asset(path, path.exists)
    yield None
    path.parent.mkdir(parents=True)
    path.touch()

@task
def cup(basedir):
    # A cup for the tea.
    path = Path(basedir) / "cup"
    yield "A cup"
    yield asset(path, path.exists)
    yield None
    path.mkdir(parents=True)

They yield their names; the asset each is responsible for readying; and the tasks they require -- None in this case, since they have no requirements. Following the final yield, they do what is necessary to ready their assets: spoon() ensures that the base directory exists, then creates the spoon file therein; cup() creates the cup directory that will contain the tea ingredients.

Note that, while pathlib's Path.mkdir() would normally raise an exception if the specified directory already exists (unless an exist_ok=True argument is supplied), the workflow need not explicitly account for this possibility because iotaa checks for the readiness of assets before executing code that would ready them. That is, iotaa will not execute the path.mkdir() statement if it determines that the asset represented by that directory is already ready (i.e. exists). This check is provided by the path.exists function supplied as the second argument to asset() in cup().

The steeped_tea_with_sugar() @task function is next:

@task
def steeped_tea_with_sugar(basedir):
    # Add sugar to the steeped tea. Requires tea to have steeped.
    for x in ingredient(basedir, "sugar", "Sugar", steeped_tea):
        yield x

Two new ideas are demonstrated here.

First, a task function can call arbitrary logic to help it carry out its duties. In this case, it calls an ingredient() helper function defined thus:

def ingredient(basedir, fn, name, req=None):
    yield f"{name} in cup"
    path = refs(cup(basedir)) / fn
    yield {fn: asset(path, path.exists)}
    yield [cup(basedir)] + ([req(basedir)] if req else [])
    logging.info("Adding %s to cup", fn)
    path.touch()

This helper is called by other task functions in the workflow, too. It simulates adding an ingredient (tea, water, sugar) to the tea cup, and yields values that the caller can re-yield to iotaa.

Second, steeped_tea_with_sugar() yields (indirectly, by passing it to ingredient()) a requirement: Sugar is added as a last step after the tea is steeped, so steeped_tea_with_sugar() requires steeped_tea(). Note that it passes the function name rather than a call (i.e. steeped_tea instead of steeped_tea(basedir)) so that it can be called at the right time by ingredient().

Next up, the steeped_tea() function, which is more complex:

@task
def steeped_tea(basedir):
    # Give tea time to steep.
    yield "Steeped tea"
    water = refs(steeping_tea(basedir))["water"]
    steep_time = lambda x: asset("elapsed time", lambda: x)
    t = 10  # seconds
    if water.exists():
        water_poured_time = dt.datetime.fromtimestamp(water.stat().st_mtime)
        ready_time = water_poured_time + dt.timedelta(seconds=t)
        now = dt.datetime.now()
        ready = now >= ready_time
        remaining = int((ready_time - now).total_seconds())
        yield steep_time(ready)
    else:
        ready = False
        remaining = t
        yield steep_time(False)
    yield steeping_tea(basedir)
    if not ready:
        logging.warning("Tea needs to steep for %ss", remaining)

Here, the asset being yielded is more abstract: It represents a certain amount of time having passed since the boiling water was poured over the tea. (The observant reader will note that 10 seconds is insufficient, if handy for a demo. Try 3 minutes for black tea IRL.) The path to the water file is located by calling refs() on the return value of steeping_tea() and taking the item with key water (because ingredient() yields its assets as {fn: asset(path, path.exists)}, where fn is the filename, e.g. sugar, teabag, water.) If the water was poured long enough ago, steeped_tea is ready; if not, it should be during some future execution of this workflow. Note that the executable code following the final yield only logs information: There's nothing this task can do to ready its asset (time passed): It can only wait.

Note the statement

water = refs(steeping_tea(basedir))["water"]

Here, steeped_tea() needs to know the path to the water file, and obtains it by calling the steeping_tea() task, extracting the references to its assets with iotaa's refs() function, and selecting the "water" item's reference, which is the path to the water file. This is a useful way to delegate ownership of knowledge about assets to those assets, but note that the function call steeping_tea(basedir) effectively transfers workflow control to that task. This can be seen in the execution traces shown later in this document, where the task responsible for the water file (as well as its requirements) are evaluated before the steep-time task.

The steeping_tea() and teabag() functions are again straightforward @tasks, leveraging the ingredient() helper:

@task
def steeping_tea(basedir):
    # Pour boiling water over the tea. Requires teabag in cup.
    for x in ingredient(basedir, "water", "Boiling water", teabag):
        yield x

@task
def teabag(basedir):
    # Place tea bag in the cup. Requires box of teabags.
    for x in ingredient(basedir, "teabag", "Teabag", box_of_teabags):
        yield x

Finally, we have this workflow's only @external task, box_of_teabags(). The idea here is that this is something that simply must exist (think: someone must have simply bought the box of teabags at the store), and no action by the workflow can create it. Unlike other task types, the @external yields, after its name, only the assets that it represents. It yields no task requirements, and has no executable statements to ready the asset:

@external
def box_of_teabags(basedir):
    path = Path(basedir) / "box-of-teabags"
    yield f"Box of teabags {path}"
    yield asset(path, path.exists)

Let's run this workflow with the iotaa command-line tool, requesting that the workflow start with the a_cup_of_tea task:

% iotaa iotaa.demo a_cup_of_tea ./teatime
[2023-10-19T11:49:43] INFO    The perfect cup of tea: Initial state: Not Ready
[2023-10-19T11:49:43] INFO    The perfect cup of tea: Checking requirements
[2023-10-19T11:49:43] INFO    A spoon: Initial state: Not Ready
[2023-10-19T11:49:43] INFO    A spoon: Checking requirements
[2023-10-19T11:49:43] INFO    A spoon: Requirement(s) ready
[2023-10-19T11:49:43] INFO    A spoon: Executing
[2023-10-19T11:49:43] INFO    A spoon: Final state: Ready
[2023-10-19T11:49:43] INFO    A cup: Initial state: Not Ready
[2023-10-19T11:49:43] INFO    A cup: Checking requirements
[2023-10-19T11:49:43] INFO    A cup: Requirement(s) ready
[2023-10-19T11:49:43] INFO    A cup: Executing
[2023-10-19T11:49:43] INFO    A cup: Final state: Ready
[2023-10-19T11:49:43] INFO    Sugar in cup: Initial state: Not Ready
[2023-10-19T11:49:43] INFO    Sugar in cup: Checking requirements
[2023-10-19T11:49:43] INFO    Boiling water in cup: Initial state: Not Ready
[2023-10-19T11:49:43] INFO    Boiling water in cup: Checking requirements
[2023-10-19T11:49:43] INFO    Teabag in cup: Initial state: Not Ready
[2023-10-19T11:49:43] INFO    Teabag in cup: Checking requirements
[2023-10-19T11:49:43] WARNING Box of teabags teatime/box-of-teabags: State: Not Ready (external asset)
[2023-10-19T11:49:43] INFO    Teabag in cup: Requirement(s) not ready
[2023-10-19T11:49:43] WARNING Teabag in cup: Final state: Not Ready
[2023-10-19T11:49:43] INFO    Boiling water in cup: Requirement(s) not ready
[2023-10-19T11:49:43] WARNING Boiling water in cup: Final state: Not Ready
[2023-10-19T11:49:43] INFO    Steeped tea: Initial state: Not Ready
[2023-10-19T11:49:43] INFO    Steeped tea: Checking requirements
[2023-10-19T11:49:43] INFO    Steeped tea: Requirement(s) not ready
[2023-10-19T11:49:43] WARNING Steeped tea: Final state: Not Ready
[2023-10-19T11:49:43] INFO    Sugar in cup: Requirement(s) not ready
[2023-10-19T11:49:43] WARNING Sugar in cup: Final state: Not Ready
[2023-10-19T11:49:43] WARNING The perfect cup of tea: Final state: Not Ready

There's lots to see during the first invocation. Most of the tasks start and end in a not-ready state. Only the spoon() and cup() tasks make progress from Not Ready to Ready states:

[2023-10-19T11:49:43] INFO    A spoon: Initial state: Not Ready
[2023-10-19T11:49:43] INFO    A spoon: Checking requirements
[2023-10-19T11:49:43] INFO    A spoon: Requirement(s) ready
[2023-10-19T11:49:43] INFO    A spoon: Executing
[2023-10-19T11:49:43] INFO    A spoon: Final state: Ready

We will see in subsequent workflow invocations that these tasks are not revisited, as their assets will be found to be ready.

The on-disk workflow state is:

% tree teatime
teatime
├── cup
└── spoon

Note the blocker:

[2023-10-19T11:49:43] WARNING Box of teabags teatime/box-of-teabags: State: Not Ready (external asset)

The file teatime/box-of-teabags cannot be created by the workflow, as it is declared @external. Let's create it externally:

% touch teatime/box-of-teabags
% tree teatime/
teatime/
├── box-of-teabags
├── cup
└── spoon

Now let's iterate the workflow:

% iotaa iotaa.demo a_cup_of_tea ./teatime
[2023-10-19T11:52:09] INFO    The perfect cup of tea: Initial state: Not Ready
[2023-10-19T11:52:09] INFO    The perfect cup of tea: Checking requirements
[2023-10-19T11:52:09] INFO    Sugar in cup: Initial state: Not Ready
[2023-10-19T11:52:09] INFO    Sugar in cup: Checking requirements
[2023-10-19T11:52:09] INFO    Boiling water in cup: Initial state: Not Ready
[2023-10-19T11:52:09] INFO    Boiling water in cup: Checking requirements
[2023-10-19T11:52:09] INFO    Teabag in cup: Initial state: Not Ready
[2023-10-19T11:52:09] INFO    Teabag in cup: Checking requirements
[2023-10-19T11:52:09] INFO    Teabag in cup: Requirement(s) ready
[2023-10-19T11:52:09] INFO    Teabag in cup: Executing
[2023-10-19T11:52:09] INFO    Adding teabag to cup
[2023-10-19T11:52:09] INFO    Teabag in cup: Final state: Ready
[2023-10-19T11:52:09] INFO    Boiling water in cup: Requirement(s) ready
[2023-10-19T11:52:09] INFO    Boiling water in cup: Executing
[2023-10-19T11:52:09] INFO    Adding water to cup
[2023-10-19T11:52:09] INFO    Boiling water in cup: Final state: Ready
[2023-10-19T11:52:09] INFO    Steeped tea: Initial state: Not Ready
[2023-10-19T11:52:09] INFO    Steeped tea: Checking requirements
[2023-10-19T11:52:09] INFO    Steeped tea: Requirement(s) ready
[2023-10-19T11:52:09] INFO    Steeped tea: Executing
[2023-10-19T11:52:09] WARNING Tea needs to steep for 9s
[2023-10-19T11:52:09] INFO    Sugar in cup: Requirement(s) not ready
[2023-10-19T11:52:09] WARNING Sugar in cup: Final state: Not Ready
[2023-10-19T11:52:09] WARNING The perfect cup of tea: Final state: Not Ready

On-disk workflow state now:

% tree teatime
teatime
├── box-of-teabags
├── cup
│   ├── teabag
│   └── water
└── spoon

Since the box of tea became available, the workflow was able to add tea to the cup and pour boiling water over it. Note the message Tea needs to steep for 9s. If we iterate the workflow again after a few seconds, we can see the steep time decreasing:

% iotaa iotaa.demo a_cup_of_tea ./teatime
...
[2023-10-19T11:52:12] WARNING Tea needs to steep for 6s
...

If we wait a bit longer and iterate:

% iotaa iotaa.demo a_cup_of_tea ./teatime
[2023-10-19T11:53:49] INFO    The perfect cup of tea: Initial state: Not Ready
[2023-10-19T11:53:49] INFO    The perfect cup of tea: Checking requirements
[2023-10-19T11:53:49] INFO    Sugar in cup: Initial state: Not Ready
[2023-10-19T11:53:49] INFO    Sugar in cup: Checking requirements
[2023-10-19T11:53:49] INFO    Sugar in cup: Requirement(s) ready
[2023-10-19T11:53:49] INFO    Sugar in cup: Executing
[2023-10-19T11:53:49] INFO    Adding sugar to cup
[2023-10-19T11:53:49] INFO    Sugar in cup: Final state: Ready
[2023-10-19T11:53:49] INFO    The perfect cup of tea: Final state: Ready

Now that the tea has steeped long enough, the sugar has been added:

% tree teatime
teatime
├── box-of-teabags
├── cup
│   ├── sugar
│   ├── teabag
│   └── water
└── spoon

One more iteration and we see that the workflow has reached its final state and takes no more action:

% iotaa iotaa.demo a_cup_of_tea ./teatime
[2023-10-19T11:54:32] INFO    The perfect cup of tea: Initial state: Not Ready
[2023-10-19T11:54:32] INFO    The perfect cup of tea: Checking requirements
[2023-10-19T11:54:32] INFO    The perfect cup of tea: Final state: Ready

Since a_cup_of_tea() is a @tasks collection, its state is contingent on that of its required tasks, so its readiness check will always involve checking requirements, unlike a non-collection @task, which can just check its assets.

One useful feature of this kind of workflow is its ability to recover from damage to its external state. Here, we remove the sugar from the tea (don't try this at home):

% rm -v teatime/cup/sugar
removed 'teatime/cup/sugar'
% tree teatime/
teatime/
├── box-of-teabags
├── cup
│   ├── teabag
│   └── water
└── spoon

Note how the workflow detects the change to the readiness of its assets and recovers:

% iotaa iotaa.demo a_cup_of_tea ./teatime
[2023-10-19T11:55:45] INFO    The perfect cup of tea: Initial state: Not Ready
[2023-10-19T11:55:45] INFO    The perfect cup of tea: Checking requirements
[2023-10-19T11:55:45] INFO    Sugar in cup: Initial state: Not Ready
[2023-10-19T11:55:45] INFO    Sugar in cup: Checking requirements
[2023-10-19T11:55:45] INFO    Sugar in cup: Requirement(s) ready
[2023-10-19T11:55:45] INFO    Sugar in cup: Executing
[2023-10-19T11:55:45] INFO    Adding sugar to cup
[2023-10-19T11:55:45] INFO    Sugar in cup: Final state: Ready
[2023-10-19T11:55:45] INFO    The perfect cup of tea: Final state: Ready

% tree teatime
teatime
├── box-of-teabags
├── cup
│   ├── sugar
│   ├── teabag
│   └── water
└── spoon

Another useful feature is the ability to enter the workflow's task graph at an arbitrary point to obtain only a subset of the assets. For example, if we'd like a cup of tea without sugar, we can start with the steeped_tea task rather than the higher-level a_cup_of_tea task.

First, let's empty the cup:

% rm -v teatime/cup/*
removed 'teatime/cup/sugar'
removed 'teatime/cup/teabag'
removed 'teatime/cup/water'
% tree teatime/
teatime/
├── box-of-teabags
├── cup
└── spoon

Now request tea without sugar:

% iotaa iotaa.demo steeped_tea ./teatime
% iotaa iotaa.demo steeped_tea ./teatime
[2023-10-19T11:57:31] INFO    Boiling water in cup: Initial state: Not Ready
[2023-10-19T11:57:31] INFO    Boiling water in cup: Checking requirements
[2023-10-19T11:57:31] INFO    Teabag in cup: Initial state: Not Ready
[2023-10-19T11:57:31] INFO    Teabag in cup: Checking requirements
[2023-10-19T11:57:31] INFO    Teabag in cup: Requirement(s) ready
[2023-10-19T11:57:31] INFO    Teabag in cup: Executing
[2023-10-19T11:57:31] INFO    Adding teabag to cup
[2023-10-19T11:57:31] INFO    Teabag in cup: Final state: Ready
[2023-10-19T11:57:31] INFO    Boiling water in cup: Requirement(s) ready
[2023-10-19T11:57:31] INFO    Boiling water in cup: Executing
[2023-10-19T11:57:31] INFO    Adding water to cup
[2023-10-19T11:57:31] INFO    Boiling water in cup: Final state: Ready
[2023-10-19T11:57:31] INFO    Steeped tea: Initial state: Not Ready
[2023-10-19T11:57:31] INFO    Steeped tea: Checking requirements
[2023-10-19T11:57:31] INFO    Steeped tea: Requirement(s) ready
[2023-10-19T11:57:31] INFO    Steeped tea: Executing
[2023-10-19T11:57:31] WARNING Tea needs to steep for 9s

After waiting for the tea to steep:

% iotaa iotaa.demo steeped_tea ./teatime
2023-10-19T11:57:57] INFO    Steeped tea: Initial state: Ready

On-disk state:

% tree teatime/
teatime/
├── box-of-teabags
├── cup
│   ├── teabag
│   └── water
└── spoon

Graphing

The -g / --graph switch can be used to emit to stdout a description of the current state of the workflow graph in Graphviz DOT format. Here, for example, the preceding demo workflow is executed in dry-run mode with graph output requested, and the graph document rendered as an SVG image by dot and displayed by the Linux utility display:

% iotaa --dry-run --graph iotaa.demo a_cup_of_tea ./teatime | display <(dot -T svg)
[2023-10-19T12:13:47] INFO    The perfect cup of tea: Initial state: Not Ready
...
[2023-10-19T12:13:47] WARNING The perfect cup of tea: Final state: Not Ready

The displayed image (tasks are ovals, assets (green => ready, orange => not ready) are rectangles):

Removing --dry-run and following the first phase of the demo tutorial in the previous section, the following succession of graph images are shown:

• First invocation, blocked by missing (external) box of teabags:

• Second invocation, with box of teabags available:

• Third invocation, waiting for tea to steep:

• Fourth invocation, with sugar added to steeped tea:

• Fifth invocation, showing final workflow sate: