## Description from docstring { #description-from-docstring }

As descriptions tend to be long and cover multiple lines, you can declare the *path operation* description in the function <abbr title="a multi-line string as the first expression inside a function (not assigned to any variable) used for documentation">docstring</abbr> and **FastAPI** will read it from there.

{* ../../docs_src/path_operation_advanced_configuration/tutorial003.py hl[6] *}

## Advanced description from docstring { #advanced-description-from-docstring }

You can limit the lines used from the docstring of a *path operation function* for OpenAPI.

Adding an `\f` (an escaped "form feed" character) causes **FastAPI** to truncate the output used for OpenAPI at this point.

It is a plug-in for many frameworks (and there's a plug-in for Starlette too).

The way it works is that you write the definition of the schema using YAML format inside the docstring of each function handling a route.

And it generates OpenAPI schemas.

That's how it works in Flask, Starlette, Responder, etc.

* Add support for truncating docstrings from *path operation functions*.
    * New docs at [Advanced description from docstring](https://fastapi.tiangolo.com/advanced/path-operation-advanced-configuration/#advanced-description-from-docstring).
    * PR [#556](https://github.com/tiangolo/fastapi/pull/556) by [@svalouch](https://github.com/svalouch).

        weighting is done on linear magnitude spectra (sqrt of inputs).
    *   Change `tf.contrib.distributions` docstring examples to use `tfd` alias
        rather than `ds`, `bs`.
    *   Fix docstring typos in `tf.distributions.bijectors.Bijector`.
    *   `tf.assert_equal` no longer raises `ValueError.` It now raises
        `InvalidArgumentError,` as documented.

        assertEquals("VERSION_2", WitnessVersion.VERSION_2.toString());

        assertEquals("RESOURCE_CHANGE", WitnessEventType.RESOURCE_CHANGE.toString());
        assertEquals("CLIENT_MOVE", WitnessEventType.CLIENT_MOVE.toString());
        assertEquals("SHARE_MOVE", WitnessEventType.SHARE_MOVE.toString());
        assertEquals("IP_CHANGE", WitnessEventType.IP_CHANGE.toString());

        String[] values = { "value1" };
        RequestParameter param = new RequestParameter(null, values);

        String expected = "[null, [value1]]";
        assertEquals(expected, param.toString());
    }

    public void test_toString_withNullValues() {
        // Test toString with null values
        String name = "testParam";
        RequestParameter param = new RequestParameter(name, null);

        Exception exception = new RuntimeException("Test error message");

        monitorTarget.appendException(buf, exception);
        assertTrue(buf.toString().startsWith("\"exception\":\""));
        assertTrue(buf.toString().contains("Test error message"));
        assertTrue(buf.toString().contains("RuntimeException"));
    }

    // Test appendException method with nested exception

    public void test_constructorWithScheduledJob() {
        // Test with scheduled job that has a custom toString implementation
        ScheduledJob scheduledJob = new ScheduledJob() {
            @Override
            public String toString() {
                return "TestScheduledJob[id=123]";
            }
        };

        String result = facetInfo.toString();
        assertEquals("FacetInfo [field=[field1, field2], query=[query1, query2], size=10, minDocCount=5, sort=count.desc, missing=unknown]",
                result);
    }

    // Test toString method with null fields
    public void test_toString_nullFields() {
        String result = facetInfo.toString();