## Dependencies

We see that we are going to need some dependencies used in several places of the application.

So we put them in their own `dependencies` module (`app/dependencies.py`).

We will now use a simple dependency to read a custom `X-Token` header:

//// tab | Python 3.9+

```Python hl_lines="3  6-8" title="app/dependencies.py"
{!> ../../docs_src/bigger_applications/app_an_py39/dependencies.py!}
```

////

https://github.com/tensorflow/tensorflow/blob/master/tensorflow/tools/tf_sig_build_dockerfiles/devel.usertools/code_check_full.bats
Here are the affected tests:
EOF
    while read dep; do
      echo "For dependency $dep:"
      # For every missing dependency, find the tests which directly depend on
      # it, and print that list for debugging. Not really clear if this is
      # helpful since the only examples I've seen are enormous.

 * A {@code PathType} can identify the Java class-path, the Java module-path,
 * or another kind of path for another programming language for example.
 * Path types are often exclusive. For example, a dependency should not be
 * both on the Java class-path and on the Java module-path.
 *
 * @see org.apache.maven.api.services.DependencyResolverResult#getDispatchedPaths()
 *
 * @since 4.0.0
 */
@Experimental

    /**
     * Transform Graph into a Collection of metadata objects that
     * could serve as a classpath for a particular scope
     *
     * @param dirtyGraph - dependency graph
     * @param scope - which classpath to extract
     * @param resolve - whether to resolve artifacts.
     * @return Collection of metadata objects in the linked subgraph of the graph which

 * under the License.
 */
package org.apache.maven.api;

import org.apache.maven.api.annotations.Experimental;
import org.apache.maven.api.annotations.Nullable;

/**
 * A dependency exclusion.
 *
 * @since 4.0.0
 * @see DependencyCoordinates#getExclusions()
 */
@Experimental
public interface Exclusion {
    @Nullable
    String getGroupId();

    @Nullable

        if (result.hasMetadataResolutionExceptions()) {
            throw result.getMetadataResolutionException(0);
        }

        // Metadata cannot be retrieved

        // Cyclic Dependency Error

        if (result.hasCircularDependencyExceptions()) {
            throw result.getCircularDependencyException(0);
        }

        // Version Range Violation

 * assist those clients that employ the repository system outside of an IoC container, Maven plugins should instead
 * always use regular dependency injection to acquire the repository system.
 *
 * @deprecated See {@link MavenSessionBuilderSupplier}
 */
@Deprecated
public final class MavenRepositorySystemUtils {

    private MavenRepositorySystemUtils() {

 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

/**
 * <a href="https://guava.dev/EventBus">Discouraged</a> in favor of dependency injection and
 * concurrency frameworks, EventBus allows publish-subscribe-style communication.
 *
 * <p>See the Guava User Guide article on <a

* Alle Schlüsselwort-Argumente, die an die Taskfunktion übergeben werden sollen (`message="some notification"`).

## Dependency Injection

    "crossVersionTests": false
  },
  {
    "name": "dependency-management",
    "path": "platforms/software/dependency-management",
    "unitTests": true,
    "functionalTests": true,
    "crossVersionTests": true
  },
  {
    "name": "dependency-management-serialization-codecs",
    "path": "platforms/core-configuration/dependency-management-serialization-codecs",
    "unitTests": false,