"msg": "Input should be a valid integer, unable to parse string as an integer",
                    "input": "foo",
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["path", "item_id"],
                    "msg": "value is not a valid integer",

!!! tip

    {!> ../../../docs_src/query_params/tutorial004.py!}
    ```

## Required query parameters

When you declare a default value for non-path parameters (for now, we have only seen query parameters), then it is not required.

If you don't want to add a specific value but just make it optional, set the default as `None`.

But when you want to make a query parameter required, you can just not declare any default value:

                    "loc": ["body", "importance"],
                    "msg": "Field required",
                    "input": None,
                },
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["body", "item"],
                    "msg": "field required",
                    "type": "value_error.missing",

                    "loc": ["body", "password"],
                    "msg": "Field required",
                    "input": None,
                },
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["body", "grant_type"],
                    "msg": "field required",
                    "type": "value_error.missing",

                                        "title": "Body",
                                    }
                                )
                                | IsDict(
                                    # TODO: remove when deprecating Pydantic v1
                                    {
                                        "$ref": "#/components/schemas/Body_create_file_files__post"
                                    }

By default it will listen on the IP address `127.0.0.1`, which is the IP for your machine to communicate with itself alone (`localhost`).

## `fastapi run`

When you run `fastapi run`, it will run on production mode by default.

    * Follow me to see when I create a new Open Source project.
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    * Hear when I make announcements or release new tools.

                            "application/json": {
                                "schema": IsDict({"$ref": "#/components/schemas/Item"})
                                | IsDict(
                                    # TODO: remove when deprecating Pydantic v1
                                    {
                                        "allOf": [
                                            {"$ref": "#/components/schemas/Item"}

                    "loc": ["body", "token"],
                    "msg": "Field required",
                    "input": None,
                },
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["body", "file"],
                    "msg": "field required",
                    "type": "value_error.missing",