This will be especially useful when you use it in a **large code base** where you use **the same dependencies** over and over again in **many *path operations***.

## To `async` or not to `async` { #to-async-or-not-to-async }

As dependencies will also be called by **FastAPI** (the same as your *path operation functions*), the same rules apply while defining your functions.

  display: inline-block;
}

a.external-link::after {
  /* \00A0 is a non-breaking space
        to make the mark be on the same line as the link
    */
  content: "\00A0[↪]";
}

a.internal-link::after {
  /* \00A0 is a non-breaking space
        to make the mark be on the same line as the link
    */
  content: "\00A0↪";
}

.shadow {
  box-shadow: 5px 5px 10px #999;
}

# Request Forms and Files { #request-forms-and-files }

You can define files and form fields at the same time using `File` and `Form`.

/// info

To receive uploaded files and/or form data, first install <a href="https://github.com/Kludex/python-multipart" class="external-link" target="_blank">`python-multipart`</a>.

Make sure you create a [virtual environment](../virtual-environments.md){.internal-link target=_blank}, activate it, and then install it, for example:

* There can be **multiple processes** of the **same program** running at the same time.

If you check out the "task manager" or "system monitor" (or similar tools) in your operating system, you will be able to see many of those processes running.

///

### Pydantic v1 and v2 on the same app { #pydantic-v1-and-v2-on-the-same-app }

It's **not supported** by Pydantic to have a model of Pydantic v2 with its own fields defined as Pydantic v1 models or vice versa.

```mermaid
graph TB
    subgraph "❌ Not Supported"

    @DisplayName("Constructor stores and exposes same array reference")
    void constructor_and_get_referenceSemantics() {
        // Arrange
        byte[] data = new byte[] { (byte) 0xDE, (byte) 0xAD, (byte) 0xBE, (byte) 0xEF };

        // Act
        SecurityBlob blob = new SecurityBlob(data);

        // Assert
        assertSame(data, blob.get(), "get() should expose the same array reference passed in");

You can define Header parameters the same way you define `Query`, `Path` and `Cookie` parameters.

## Import `Header` { #import-header }

First import `Header`:

{* ../../docs_src/header_params/tutorial001_an_py310.py hl[3] *}

## Declare `Header` parameters { #declare-header-parameters }

Then declare the header parameters using the same structure as with `Path`, `Query` and `Cookie`.

   * even in the same order. (It is guaranteed to return true for instances constructed from the
   * same values in the same order if {@code strictfp} is in effect, or if the system architecture
   * guarantees {@code strictfp}-like semantics.)
   */
  @Override
  public boolean equals(@Nullable Object obj) {
    if (obj == null) {
      return false;
    }
    if (getClass() != obj.getClass()) {
      return false;
    }

        // Second call should return cached value (same as first)
        Subject second = auth.getSubject();
        if (first == null && second == null) {
            // Both null - caching is working
            assertNull(second, "Second getSubject should return same result as first (both null)");
        } else if (first != null && second != null) {
            // Both non-null - should be same instance

import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Specifies the priority of a bean implementation when multiple implementations
 * of the same type are available.
 * <p>
 * Higher values indicate higher priority. When multiple implementations of the same
 * type exist, the one with the highest priority will be selected for injection.
 * <p>
 * Example usage:
 * <pre>
 * {@literal @}Priority(100)