{* ../../docs_src/stream_data/tutorial002_py310.py ln[23:27] hl[23] *}

### Simulate a File { #simulate-a-file }

In this example, we are simulating a file with `io.BytesIO`, which is a file-like object that lives only in memory, but lets us use the same interface.

For example, we can iterate over it to consume its contents, as we could with a file.

It is just a standard function that can receive parameters.

It can be an `async def` or normal `def` function, **FastAPI** will know how to handle it correctly.

In this case, the task function will write to a file (simulating sending an email).

And as the write operation doesn't use `async` and `await`, we define the function with normal `def`:

{* ../../docs_src/background_tasks/tutorial001_py310.py hl[6:9] *}

   * {@link IllegalArgumentException} if passed a {@code toKey} greater than an earlier {@code
   * toKey}. However, this method doesn't throw an exception in that situation, but instead keeps
   * the original {@code toKey}.
   */
  @Override
  public ImmutableSortedMap<K, V> headMap(K toKey) {
    return headMap(toKey, false);
  }

  /**

        assertEquals("", emptyUnicodeStringFalse.toString(), "toString should return empty string for empty input without zterm");

        // Test toString with a manually constructed UnicodeString (simulating rpc.unicode_string input)
        rpc.unicode_string dummyRus = new rpc.unicode_string();
        dummyRus.buffer = new short[] { 'T', 'e', 's', 't', 'i', 'n', 'g' };
        dummyRus.length = 14; // 7 characters * 2 bytes/char

import java.util.Comparator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.function.Function;
import java.util.stream.Collector;
import org.jspecify.annotations.Nullable;

/**
 * GWT emulation of {@link com.google.common.collect.ImmutableBiMap}.
 *
 * @author Hayward Chan
 */
public abstract class ImmutableBiMap<K, V> extends ForwardingImmutableMap<K, V>
    implements BiMap<K, V> {

	arm.ABPL,
	arm.ABVS,
	arm.ABVC,
	arm.ABHI,
	arm.ABLS,
	arm.ABGE,
	arm.ABLT,
	arm.ABGT,
	arm.ABLE,
	arm.AB,
	obj.ANOP,
}

// ARMConditionCodes handles the special condition code situation for the ARM.
// It returns a boolean to indicate success; failure means cond was unrecognized.
func ARMConditionCodes(prog *obj.Prog, cond string) bool {
	if cond == "" {
		return true
	}

  /** JavaLangAccess class name to load using reflection */
  @J2ktIncompatible @GwtIncompatible // not used by GWT emulation
  private static final String JAVA_LANG_ACCESS_CLASSNAME = "sun.misc.JavaLangAccess";

  /** SharedSecrets class name to load using reflection */
  @J2ktIncompatible
  @GwtIncompatible // not used by GWT emulation
  @VisibleForTesting
  static final String SHARED_SECRETS_CLASSNAME = "sun.misc.SharedSecrets";

  @Override
  ContiguousSet<C> tailSetImpl(C fromElement, boolean inclusive) {
    return intersectionInCurrentDomain(Range.downTo(fromElement, BoundType.forBoolean(inclusive)));
  }

  @GwtIncompatible // not used by GWT emulation
  @Override
  int indexOf(@Nullable Object target) {
    if (!contains(target)) {
      return -1;
    }
    // The cast is safe because of the contains check—at least for any reasonable Comparable class.

    // below the values of characters in surrogate pairs, this cannot occur.
    // This approach does mean that we break out of the fast path code in cases
    // where we don't strictly need to, but this situation will almost never
    // occur in practice.
    if (safeMin >= Character.MIN_HIGH_SURROGATE) {
      // The safe range is empty or the all safe code points lie in or above the

   * if Fire.run is called by delegate.addListener since addListener is called after the assignment
   * to timer, and importantly this is the main situation in which we need to be able to see the
   * write.
   *
   * 2. visibility of the writes to an afterDone() call triggered by cancel():
   *