# Body - Fields

The same way you can declare additional validation and metadata in *path operation function* parameters with `Query`, `Path` and `Body`, you can declare validation and metadata inside of Pydantic models using Pydantic's `Field`.

## Import `Field`

First, you have to import it:

{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[4] *}


/// warning

  env | grep ^TFCI_ > "$env_file"

  WORKING_DIR="$TFCI_GIT_DIR"
  if [[ `uname -s | grep -P '^MSYS_NT'` ]]; then
    env_file=$(cygpath -m $env_file)
    # Host dirs can only be mapped to an existing drive inside the container, so
    # T:\ is replaced with C:\.
    _TFCI_OUTPUT_DIR_WIN=$(replace_drive_letter_with_c "$TFCI_OUTPUT_DIR")
    sed -iE 's|^TFCI_OUTPUT_DIR=.*|TFCI_OUTPUT_DIR='"$_TFCI_OUTPUT_DIR_WIN"'|g' $env_file

////

## 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.

	if !globalCallhomeConfig.Enabled() {
		return
	}

	go func() {
		r := rand.New(rand.NewSource(time.Now().UnixNano()))
		// Leader node (that successfully acquires the lock inside runCallhome)
		// will keep performing the callhome. If the leader goes down for some reason,
		// the lock will be released and another node will acquire it and take over
		// because of this loop.
		for {

This won't happen if you import that module (file).

So, if you have another file `importer.py` with:

```Python
from myapp import app

# Some more code
```

in that case, the automatically created variable inside of `myapp.py` will not have the variable `__name__` with a value of `"__main__"`.

So, the line:

```Python
    uvicorn.run(app, host="0.0.0.0", port=8000)
```

will not be executed.

/// info

Il a clairement inspiré Uvicorn et Starlette, qui sont actuellement plus rapides que Sanic dans les benchmarks.

///

/// check | "A inspiré **FastAPI** à"

Trouvez un moyen d'avoir une performance folle.

C'est pourquoi **FastAPI** est basé sur Starlette, car il s'agit du framework le plus rapide disponible (testé par des benchmarks tiers).

///

  # $TF_VER_FULL will resolve to e.g. "2.15.0-rc2". Since $TF_VER_FULL comes
  # from get_versions.sh, which must be run *after* update_version.py, FINAL_URI
  # can't be set inside the rest of the _upload envs.
  FINAL_URI="$TFCI_ARTIFACT_FINAL_GCS_URI/$TF_VER_FULL"
  gsutil -m rsync -d -r "$DOWNLOADS" "$FINAL_URI"

  # Also mirror the latest-uploaded folder to the "latest" directory.

## Create an instance

We could create an instance of this class with:

{* ../../docs_src/dependencies/tutorial011_an_py39.py hl[18] *}

And that way we are able to "parameterize" our dependency, that now has `"bar"` inside of it, as the attribute `checker.fixed_content`.

## Use the instance as a dependency

You write standard Python with types:

```Python
from datetime import date

from pydantic import BaseModel

# Declare a variable as a str
# and get editor support inside the function
def main(user_id: str):
    return user_id


# A Pydantic model
class User(BaseModel):
    id: int
    name: str
    joined: date
```

That can then be used like:

```Python

 * conformance of concrete {@link SortedMap} subclasses to that contract.
 *
 * @author Jared Levy
 */
// TODO: Use this class to test classes besides ImmutableSortedMap.
@GwtCompatible
public abstract class SortedMapInterfaceTest<K, V> extends MapInterfaceTest<K, V> {

  protected SortedMapInterfaceTest(
      boolean allowsNullKeys,
      boolean allowsNullValues,