# Helptext generation

In addition to type annotations, :func:`tyro.cli()` will also parse docstrings
and comments. These are used to automatically generate helptext; see examples
for how these end up being formatted.

## General callables

For general callables, field helptext is extracted from the corresponding field
docstring. Our examples use Google-style docstrings, but ReST, Numpydoc-style
and Epydoc docstrings are supported as well. Under the hood, all of these
options use [docstring_parser](https://github.com/rr-/docstring_parser).

```python
def main(field1: str, field2: int = 3) -> None:
    """Function, whose arguments will be populated from a CLI interface.

    Args:
        field1: A string field.
        field2: A numeric field, with a default value.
    """
    print(field1, field2)
```

## Dataclasses, TypedDict, NamedTuple

For types defined using class attributes, enumerating each argument list in the
class docstring can be cumbersome.

If they are unavailable, :func:`tyro.cli` will generate helptext from
docstrings and comments on attributes. These are parsed via source code
inspection.

**(1) Attribute docstrings**

As per [PEP 257](https://peps.python.org/pep-0257/#what-is-a-docstring).

```python
@dataclasses.dataclass
class Args:
    field1: str
    """A string field."""
    field2: int = 3
    """A numeric field, with a default value."""
```

**(2) Inline comments**

Inline comments can be more succinct than true attribute docstrings.

```python
@dataclasses.dataclass
class Args:
    field1: str  # A string field.
    field2: int = 3  # A numeric field, with a default value.
```

**(3) Preceding comments**

These can also be handy for semantically grouping fields, such as the two string
fields below.

```python
@dataclasses.dataclass
class Args:
    # String fields.
    field1: str
    field2: str

    # An integer field.
    # Multi-line comments are supported.
    field3: int
```