### The callback path expression

The callback *path* can have an <a href="https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.1.0.md#key-expression" class="external-link" target="_blank">OpenAPI 3 expression</a> that can contain parts of the original request sent to *your API*.

In this case, it's the `str`:

## Requirements

FastAPI stands on the shoulders of giants:

* <a href="https://www.starlette.io/" class="external-link" target="_blank">Starlette</a> for the web parts.
* <a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a> for the data parts.

## Installation

<div class="termy">

```console
$ pip install fastapi

---> 100%
```

</div>

## Example

## Requirements

FastAPI stands on the shoulders of giants:

* <a href="https://www.starlette.io/" class="external-link" target="_blank">Starlette</a> for the web parts.
* <a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a> for the data parts.

## Installation

<div class="termy">

```console
$ pip install fastapi

---> 100%
```

</div>

## Example

* Be careful when using features introduced in Java 1.7 or later. Some parts of Gradle still need to run on Java 6.
* Normalize file paths in tests. The `org.gradle.util.internal.TextUtil` class has some useful functions for this purpose.

Setting options in `include_router` still makes sense in some cases, for example, to override or increase configurations from a third party router included in an app. But in a router that is part of a bigger application, it would probably make more sense to add those settings when creating the `APIRouter`.

**In `FastAPI`**

    And the `--root-path` command line option provides that `root_path`.

### Checking the current `root_path`

You can get the current `root_path` used by your application for each request, it is part of the `scope` dictionary (that's part of the ASGI spec).

Here we are including it in the message just for demonstration purposes.

```Python hl_lines="8"
{!../../../docs_src/behind_a_proxy/tutorial001.py!}
```

This will be the main point of interaction to create all your API.

### Step 3: create a *path operation*

#### Path

"Path" here refers to the last part of the URL starting from the first `/`.

So, in a URL like:

```
https://example.com/items/foo
```

...the path would be:

```
/items/foo
```

!!! info

# I tried to make this dependent on what I thought was the appropriate
# lock file, but it caused the rule for that file to get run (which
# seems to be about obtaining a new version of the 3rd party libraries).
$(TARGET_OUT)/istio_is_init: bin/init.sh istio.deps | $(TARGET_OUT)
	@# Add a retry, as occasionally we see transient connection failures to GCS
	@# Like `curl: (56) OpenSSL SSL_read: SSL_ERROR_SYSCALL, errno 104`