### Step 4: define the **path operation function**

This is our "**path operation function**":

* **path**: is `/`.
* **operation**: is `get`.
* **function**: is the function below the "decorator" (below `@app.get("/")`).

```Python hl_lines="7"
{!../../../docs_src/first_steps/tutorial001.py!}
```

This is a Python function.

        }
      };

  /* Helper function to make a BigInteger value from a Long. */
  private static final Function<Long, BigInteger> TO_BIGINTEGER =
      new Function<Long, BigInteger>() {
        @Override
        public BigInteger apply(Long n) {
          return BigInteger.valueOf(n);
        }
      };

  private static final Function<Integer, Integer> NEGATE_INT =
      new Function<Integer, Integer>() {
        @Override

      Collection<F> fromCollection, Function<? super F, T> function) {
    return new TransformedCollection<>(fromCollection, function);
  }

  static class TransformedCollection<F extends @Nullable Object, T extends @Nullable Object>
      extends AbstractCollection<T> {
    final Collection<F> fromCollection;
    final Function<? super F, ? extends T> function;

   */
  public final <T extends @Nullable Object> FluentIterable<T> transform(
      Function<? super E, T> function) {
    return from(Iterables.transform(getDelegate(), function));
  }

  /**
   * Applies {@code function} to each element of this fluent iterable and returns a fluent iterable
   * with the concatenated combination of results. {@code function} returns an Iterable of results.
   *

        }
      };

  /* Helper function to make a BigInteger value from a Long. */
  private static final Function<Long, BigInteger> TO_BIGINTEGER =
      new Function<Long, BigInteger>() {
        @Override
        public BigInteger apply(Long n) {
          return BigInteger.valueOf(n);
        }
      };

  private static final Function<Integer, Integer> NEGATE_INT =
      new Function<Integer, Integer>() {
        @Override

      implements Serializable {
    private final Function<? super A, ? extends B> forwardFunction;
    private final Function<? super B, ? extends A> backwardFunction;

    private FunctionBasedConverter(
        Function<? super A, ? extends B> forwardFunction,
        Function<? super B, ? extends A> backwardFunction) {
      this.forwardFunction = checkNotNull(forwardFunction);

    }
  }

  private static String encode(String str) {
    return BaseEncoding.base64().encode(str.getBytes(Charsets.UTF_8));
  }

  private static final Function<String, String> DECODE_FUNCTION =
      new Function<String, String>() {
        @Override
        public String apply(String input) {
          return new String(BaseEncoding.base64().decode(input), Charsets.UTF_8);
        }
      };

                      });
      fail("Should throw if Function returns null.");
    } catch (NullPointerException expected) {
    }
  }

  public void testTransform_absent_functionReturnsNull() {
    assertEquals(
        Optional.absent(),
        Optional.absent()
            .transform(
                (Function<Object, Object>)
                    new Function<Object, @Nullable Object>() {

          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction) {
    throw new UnsupportedOperationException();
  }

  /**
   * Not supported. This method does not make sense for {@code BiMap}. This method exists only to
   * hide {@link ImmutableMap#toImmutableMap(Function, Function, BinaryOperator)} from consumers of

                               TF_Status* status) {
  tensorflow::FunctionDef function_def;
  if (!function_def.ParseFromArray(serialized_function_def, size)) {
    status->status =
        tensorflow::errors::InvalidArgument("Invalid FunctionDef proto");
    return;
  }

  AnnotateEagerRuntimeConstructionContext(function_def);