# Development - Contributing

First, you might want to see the basic ways to [help FastAPI and get help](help-fastapi.md){.internal-link target=_blank}.

## Developing

If you already cloned the <a href="https://github.com/fastapi/fastapi" class="external-link" target="_blank">fastapi repository</a> and you want to deep dive in the code, here are some guidelines to set up your environment.

### Virtual environment

        service.startAsync();
      } catch (IllegalStateException e) {
        // This can happen if the service has already been started or stopped (e.g. by another
        // service or listener). Our contract says it is safe to call this method if
        // all services were NEW when it was called, and this has already been verified above, so we
        // don't propagate the exception.

   * at {@code node} and ending at {@code v}. This implementation includes {@code node} as the first
   * element in the result.
   *
   * <p>If needed, the {@link Traverser} class provides more flexible and lighter-weight ways to
   * list the nodes reachable from a given node or nodes. See the <a
   * href="https://github.com/google/guava/wiki/GraphsExplained#Graph-traversal">"Graph traversal"

   * at {@code node} and ending at {@code v}. This implementation includes {@code node} as the first
   * element in the result.
   *
   * <p>If needed, the {@link Traverser} class provides more flexible and lighter-weight ways to
   * list the nodes reachable from a given node or nodes. See the <a
   * href="https://github.com/google/guava/wiki/GraphsExplained#Graph-traversal">"Graph traversal"

				fmt.Fprint(h, meta.TransitionStatus)
				fmt.Fprint(h, meta.TransitionTier)
				fmt.Fprint(h, meta.TransitionedObjName)
				fmt.Fprint(h, meta.TransitionVersionID)
			}

			// If metadata says encrypted, ask for it in quorum.
			if etyp, ok := crypto.IsEncrypted(meta.Metadata); ok {
				fmt.Fprint(h, etyp)
			}

			// If compressed, look for compressed FileInfo only
			if meta.IsCompressed() {

       * valid value. That's the best we can do, short of holding a reference to the most recently
       * seen value. And while we *could* do that, we aren't required to: Map.Entry explicitly says
       * that behavior is undefined when the backing map is modified through another API. (It even
       * permits us to throw IllegalStateException. Maybe we should have done that, but we probably

/**
 * A bundle of statistical summary values -- sum, count, mean/average, min and max, and several
 * forms of variance -- that were computed from a single set of zero or more floating-point values.
 *
 * <p>There are two ways to obtain a {@code Stats} instance:
 *
 * <ul>
 *   <li>If all the values you want to summarize are already known, use the appropriate {@code

       * valid value. That's the best we can do, short of holding a reference to the most recently
       * seen value. And while we *could* do that, we aren't required to: Map.Entry explicitly says
       * that behavior is undefined when the backing map is modified through another API. (It even
       * permits us to throw IllegalStateException. Maybe we should have done that, but we probably

}

// A Header represents a single header in a tar archive.
// Some fields may not be populated.
//
// For forward compatibility, users that retrieve a Header from Reader.Next,
// mutate it in some ways, and then pass it back to Writer.WriteHeader
// should do so by creating a new Header and copying the fields
// that they are interested in preserving.
type Header struct {
	// Typeflag is the type of header entry.

an older Go version, the Go toolchain amends its defaults
to match that older Go version as closely as possible.
For example, when a Go 1.21 toolchain compiles a program,
if the work module's `go.mod` or the workspace's `go.work`
says `go` `1.20`, then the program defaults to `panicnil=1`,
matching Go 1.20 instead of Go 1.21.

Because this method of setting GODEBUG defaults was introduced only in Go 1.21,