# Bigger Applications - Multiple Files

If you are building an application or a web API, it's rarely the case that you can put everything in a single file.

**FastAPI** provides a convenience tool to structure your application while keeping all the flexibility.

/// info

If you come from Flask, this would be the equivalent of Flask's Blueprints.

///

## An example file structure

Let's say you have a file structure like this:

```

The `security_scopes` object (of class `SecurityScopes`) also provides a `scope_str` attribute with a single string, containing those scopes separated by spaces (we are going to use it).

We create an `HTTPException` that we can reuse (`raise`) later at several points.

			if err := loader(ctx, m, c, b); err != nil {
				return err
			}
		}
		return nil
	}
}

// MetricsGroup - represents a group of metrics. It includes a `MetricsLoaderFn`
// function that provides a way to load the metrics from the system. The metrics
// are cached and refreshed after a given timeout.
//
// For metrics with a `bucket` dimension, a list of buckets argument is required
// to collect the metrics.
//

And you can use directly many well maintained and widely used packages like `passlib` and `PyJWT`, because **FastAPI** doesn't require any complex mechanisms to integrate external packages.

But it provides you the tools to simplify the process as much as possible without compromising flexibility, robustness, or security.

And you can use and implement secure, standard protocols, like OAuth2 in a relatively simple way.

That means that any value read in Python from an environment variable will be a `str`, and any conversion to a different type or any validation has to be done in code.

## Pydantic `Settings`

Fortunately, Pydantic provides a great utility to handle these settings coming from environment variables with <a href="https://docs.pydantic.dev/latest/concepts/pydantic_settings/" class="external-link" target="_blank">Pydantic: Settings management</a>.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Provides utility methods for working with {@linkplain File files}.
 *
 * <p>{@link java.nio.file.Path} users will find similar utilities in {@link MoreFiles} and the
 * JDK's {@link java.nio.file.Files} class.
 *

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

/*
Package builtin provides documentation for Go's predeclared identifiers.
The items documented here are not actually in package builtin
but their descriptions here allow godoc to present documentation
for the language's special identifiers.
*/
package builtin

import "cmp"

		constructor() {
			this.argv = ["js"];
			this.env = {};
			this.exit = (code) => {
				if (code !== 0) {
					console.warn("exit code:", code);
				}
			};
			this._exitPromise = new Promise((resolve) => {
				this._resolveExitPromise = resolve;
			});
			this._pendingEvent = null;
			this._scheduledTimeouts = new Map();
			this._nextCallbackTimeoutID = 1;

			const setInt64 = (addr, v) => {

 *   <li>{@link StandardCharsets#US_ASCII} specifies the {@code Charset} of ASCII characters.
 *   <li>{@link CharMatcher#ascii} matches ASCII characters and provides text processing methods
 *       which operate only on the ASCII characters of a string.
 * </ul>
 *
 * @author Catherine Berry
 * @author Gregory Kick
 * @since 7.0
 */
@GwtCompatible

    assertTrue(Arrays.equals(I18N.getBytes(UTF_8), Files.toByteArray(i18nFile)));
    assertTrue(Arrays.equals(I18N.getBytes(UTF_8), Files.asByteSource(i18nFile).read()));
  }

  /** A {@link File} that provides a specialized value for {@link File#length()}. */
  private static class BadLengthFile extends File {

    private final long badLength;

    public BadLengthFile(File delegate, long badLength) {