**FastAPI** knows what to do in each case and how to reuse the same object, so that all the background tasks are merged together and are run in the background afterwards:


{* ../../docs_src/background_tasks/tutorial002_an_py310.py hl[13,15,22,25] *}

irrevocably and unconditionally waives, abandons, and surrenders all of
Affirmer's Copyright and Related Rights and associated claims and causes
of action, whether now known or unknown (including existing as well as
future claims and causes of action), in the Work (i) in all territories
worldwide, (ii) for the maximum duration provided by applicable law or

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[9] *}

But then we get a `dict` in the parameter `commons` of the *path operation function*.

And we know that editors can't provide a lot of support (like completion) for `dict`s, because they can't know their keys and value types.

We can do better...

## What makes a dependency { #what-makes-a-dependency }

Up to now you have seen dependencies declared as functions.

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[23] *}

/// info

Notice that we are only declaring one dependency in the *path operation function*, the `query_or_cookie_extractor`.

But **FastAPI** will know that it has to solve `query_extractor` first, to pass the results of that to `query_or_cookie_extractor` while calling it.

///

```mermaid
graph TB

query_extractor(["query_extractor"])

    if (mapEntryBelowToTruncate != null) {
      // we know ( [
      RangeMapEntry<K, V> rangeMapEntry = mapEntryBelowToTruncate.getValue();
      if (rangeMapEntry.getUpperBound().compareTo(rangeToRemove.lowerBound) > 0) {
        // we know ( [ )
        if (rangeMapEntry.getUpperBound().compareTo(rangeToRemove.upperBound) > 0) {
          // we know ( [ ] ), so insert the range ] ) back into the map --

     *   <li>If this field's value is some other thread object, we know that it's not our thread.
     *   <li>If this field's value == null because it originally belonged to another thread and that
     *       thread cleared it, we still know that it's not associated with our thread
     *   <li>If this field's value == null because it was associated with our thread and was
     *       cleared, we know that we're not executing inline any more
     * </ul>

This dependency will provide a `str` that is assigned to the parameter `token` of the *path operation function*.

**FastAPI** will know that it can use this dependency to define a "security scheme" in the OpenAPI schema (and the automatic API docs).

/// info | Technical Details

   
   *Please let us know if this helps.*
   
windows_comment: >
   From the stack trace it looks like you are hitting windows path length limit.
      * Try to disable path length limit on Windows 10.
        * Refer [disable path length limit instructions guide.](https://mspoweruser.com/ntfs-260-character-windows-10/)
   

The query parameter `q` is of type `str | None`, that means that it's of type `str` but could also be `None`, and indeed, the default value is `None`, so FastAPI will know it's not required.

/// note

FastAPI will know that the value of `q` is not required because of the default value `= None`.

Having `str | None` will allow your editor to give you better support and detect errors.

///

    for (LoadingCache<Object, Object> cache : caches()) {
      cache.getUnchecked(1);
      cache.getUnchecked(2);

      Set<Object> keys = cache.asMap().keySet();
      // We don't know whether these are still in the cache, so we can't assert on the return
      // values of these removes, but the cache should be empty after the removes, regardless.
      keys.remove(1);
      keys.remove(2);