### Tags with Enums { #tags-with-enums }

If you have a big application, you might end up accumulating **several tags**, and you would want to make sure you always use the **same tag** for related *path operations*.

In these cases, it could make sense to store the tags in an `Enum`.

**FastAPI** supports that the same way as with plain strings:

{* ../../docs_src/path_operation_configuration/tutorial002b_py39.py hl[1,8:10,13,18] *}

    checkFromStringCase("google.com:25\t", 1, null, 99, false);
    checkFromStringCase("google.com:0x25 ", 1, null, 99, false);
  }

  public void testFromStringUnparseableNonsense() {
    // Some nonsense that causes parse failures.
    checkFromStringCase("[goo.gl]", 1, null, 99, false);
    checkFromStringCase("[goo.gl]:80", 1, null, 99, false);
    checkFromStringCase("[", 1, null, 99, false);

    checkFromStringCase("google.com:25\t", 1, null, 99, false);
    checkFromStringCase("google.com:0x25 ", 1, null, 99, false);
  }

  public void testFromStringUnparseableNonsense() {
    // Some nonsense that causes parse failures.
    checkFromStringCase("[goo.gl]", 1, null, 99, false);
    checkFromStringCase("[goo.gl]:80", 1, null, 99, false);
    checkFromStringCase("[", 1, null, 99, false);

     * be {@code a -> c}.
     * <p>
     * Original code would falsely report {@code a} project as "without dependencies", basically would lose link due
     * filtering. This causes build ordering issues in concurrent builders.
     */
    private List<MavenProject> applyFilter(
            Collection<? extends MavenProject> projects, boolean transitive, boolean upstream) {

        assertEscaping(xmlEscaper, "\uFFFD", ch);
      }
    }

    // Test _all_ allowed characters (including surrogate values).
    for (char ch = 0x20; ch <= 0xFFFD; ch++) {
      // There are a small number of cases to consider, so just do it manually.
      if (ch == '&') {
        assertEscaping(xmlEscaper, "&amp;", ch);
      } else if (ch == '<') {
        assertEscaping(xmlEscaper, "&lt;", ch);
      } else if (ch == '>') {

---

**Note**: You can mix `def` and `async def` in your *path operation functions* as much as you need and define each one using the best option for you. FastAPI will do the right thing with them.

Anyway, in any of the cases above, FastAPI will still work asynchronously and be extremely fast.

But by following the steps above, it will be able to do some performance optimizations.

## Technical Details { #technical-details }

    'ignore:datetime\.datetime\.utcfromtimestamp\(\) is deprecated and scheduled for removal in a future version\..*:DeprecationWarning:sqlalchemy',
    # Trio 24.1.0 raises a warning from attrs
    # Ref: https://github.com/python-trio/trio/pull/3054
    # Remove once there's a new version of Trio
    'ignore:The `hash` argument is deprecated*:DeprecationWarning:trio',
]

  }

  ImmutableMap<K, V> getAllPresent(Iterable<?> keys) {
    int hits = 0;
    int misses = 0;

    ImmutableMap.Builder<K, V> result = ImmutableMap.builder();
    for (Object key : keys) {
      V value = get(key);
      if (value == null) {
        misses++;
      } else {
        // TODO(fry): store entry key instead of query key
        @SuppressWarnings("unchecked")

    * So, by using FastAPI you are saving development time, bugs, lines of code, and you would probably get the same performance (or better) you would...

///

## Forbid Extra Cookies { #forbid-extra-cookies }

In some special use cases (probably not very common), you might want to **restrict** the cookies that you want to receive.