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.. _Getting Started:
===============
Getting Started
===============
Cyclopts relies heavily on function parameter type hints.
If you are new to type hints or need a refresher, `checkout the mypy cheatsheet`_.
----------------------------
A Basic Cyclopts Application
----------------------------
The most basic Cyclopts application is as follows:
.. code-block:: python
from cyclopts import App
app = App()
@app.default
def main():
print("Hello World!")
if __name__ == "__main__":
app()
Save this as ``main.py`` and execute it to see:
.. code-block:: console
$ python main.py
Hello World!
The :class:`.App` class offers various configuration options that we'll explore in more detail later.
The ``app`` object has a decorator method, :meth:`default <cyclopts.App.default>`, which registers a function as the **default action**.
In this example, the ``main`` function is our default action, and is executed when no CLI command is provided.
------------------
Function Arguments
------------------
Let's add some arguments to make this program a little more interesting.
.. code-block:: python
from cyclopts import App
app = App()
@app.default
def main(name):
print(f"Hello {name}!")
if __name__ == "__main__":
app()
Executing the script with the argument ``Alice`` produces the following:
.. code-block:: console
$ python main.py Alice
Hello Alice!
Code explanation:
1. The function ``main()`` was registered to ``app`` as the **default** action.
2. Calling ``app()`` at the bottom triggers the app to begin parsing CLI inputs.
3. Cyclopts identifies ``"Alice"`` as a positional argument and matches it to the parameter ``name``.
In the absence of an explicit type hint, Cyclopts defaults to parsing the value as a ``str``.
.. note::
Without a type annotation, Cyclopts will actually first attempt to use the **type** of
the parameter's **default value**. If the parameter doesn't have a default value, it will
then fallback to ``str``. See :ref:`Coercion Rules`.
4. Cyclopts calls the registered **default** function ``main("Alice")``, and the greeting is printed.
------------------
Multiple Arguments
------------------
Extending the example, lets add more arguments and type hints:
.. code-block:: python
from cyclopts import App
app = App()
@app.default
def main(name: str, count: int, formal: bool = False):
for _ in range(count):
if formal:
print(f"Hello {name}!")
else:
print(f"Hey {name}!")
if __name__ == "__main__":
app()
.. code-block:: console
$ python main.py Alice 3
Hey Alice!
Hey Alice!
Hey Alice!
$ python main.py Alice 3 --formal
Hello Alice!
Hello Alice!
Hello Alice!
The command line input ``"3"`` is converted to an integer because the parameter ``count`` has the type hint :obj:`int`.
Boolean ( here, ``--formal``) parameters are interpreted as flags.
Cyclopts natively handles all python builtin types (:ref:`and more! <Coercion Rules>`).
Cyclopts adheres to Python's argument binding rules, allowing for both positional and keyword arguments.
All of the following CLI invocations are equivalent:
.. code-block:: console
$ python main.py Alice 3 # Supplying arguments positionally.
$ python main.py --name Alice --count 3 # Supplying arguments via keywords.
$ python main.py --name=Alice --count=3 # Using = for matching keywords to values is allowed.
$ python main.py --count 3 --name=Alice # Keyword order does not matter.
$ python main.py Alice --count 3 # positional followed by keyword
$ python main.py --count 3 Alice # Keywords can come before positional if the keyword is later in the function signature.
Like calling functions in python, positional arguments cannot be specified after a **prior** argument in the function signature was specified via keyword.
For example, you cannot supply the count value ``"3"`` positionally while the value for ``name`` is specified via keyword:
.. code-block:: bash
# The following are NOT allowed.
$ python main.py --name=Alice 3 # invalid python: main(name="Alice", 3)
$ python main.py 3 --name=Alice # invalid python: main(3, name="Alice")
------------------
Adding a Help Page
------------------
All CLI apps need to have a help page explaining how to use the application.
By default, Cyclopts adds the ``--help`` (and the shortform ``-h``) commands to your CLI.
We can add application-level help documentation when creating our ``app``:
.. code-block:: python
from cyclopts import App
app = App(help="Help string for this demo application.")
@app.default
def main(name: str, count: int):
for _ in range(count):
print(f"Hello {name}!")
if __name__ == "__main__":
app()
.. code-block:: console
$ python main.py --help
Usage: main COMMAND [ARGS] [OPTIONS]
Help string for this demo application.
╭─ Commands ──────────────────────────────────────────────────────────╮
│ --help -h Display this message and exit. │
│ --version Display application version. │
╰─────────────────────────────────────────────────────────────────────╯
╭─ Parameters ────────────────────────────────────────────────────────╮
│ * NAME --name [required] │
│ * COUNT --count [required] │
╰─────────────────────────────────────────────────────────────────────╯
.. note::
Help flags can be changed with :attr:`~cyclopts.App.help_flags`.
Let's add some help documentation for our parameters.
Cyclopts uses the function's docstring and can interpret ReST, Google, Numpydoc-style and Epydoc docstrings (shoutout to `docstring_parser <https://github.com/rr-/docstring_parser>`_).
.. code-block:: python
from cyclopts import App
app = App()
@app.default
def main(name: str, count: int):
"""Help string for this demo application.
Parameters
----------
name: str
Name of the user to be greeted.
count: int
Number of times to greet.
"""
for _ in range(count):
print(f"Hello {name}!")
if __name__ == "__main__":
app()
.. code-block:: console
$ python main.py --help
Usage: main COMMAND [ARGS] [OPTIONS]
Help string for this demo application.
╭─ Commands ──────────────────────────────────────────────────────────╮
│ --help -h Display this message and exit. │
│ --version Display application version. │
╰─────────────────────────────────────────────────────────────────────╯
╭─ Parameters ────────────────────────────────────────────────────────╮
│ * NAME --name Name of the user to be greeted. [required] │
│ * COUNT --count Number of times to greet. [required] │
╰─────────────────────────────────────────────────────────────────────╯
.. note::
If :attr:`.App.help` is not explicitly set, Cyclopts will fallback to the first line
(short description) of the registered ``@app.default`` function's docstring.
---
Run
---
An alternative, terser API is available for simple applications with a single command.
The :func:`.run` function takes in a single callable (usually a function) and runs it
as a Cyclopts application.
.. code-block:: python
import cyclopts
def main(name: str, count: int):
for _ in range(count):
print(f"Hello {name}!")
if __name__ == "__main__":
cyclopts.run(main)
The :func:`.run` function is intentionally simple. If greater control is required, then use the
conventional :class:`.App` interface.
.. _checkout the mypy cheatsheet: https://mypy.readthedocs.io/en/latest/cheat_sheet_py3.html
|
