Flask Request Object

Flask is a popular web framework in Python that allows developers to build web applications easily and quickly. One of the key features of Flask is its request object, which allows developers to access information from incoming requests. In this article, we’ll explore the Flask request object, its properties, and methods, and how to use it in a Flask application.

What is Flask Request Object?

Flask request object is a container for all incoming HTTP request data. It contains information about the request method, headers, URL parameters, cookies, and request data. The Flask request object is created automatically by Flask when a request is received and is available within the request context. The request context is a temporary environment where Flask processes the request, and it is available throughout the lifecycle of a request.

Accessing Flask Request Object

To access the Flask request object, you need to import the request module from the Flask package. The request object is an instance of the Request class.

from flask import Flask, request

app = Flask(__name__)

@app.route('/')
def index():
    print(request.method)
    print(request.headers)
    print(request.args)
    print(request.form)
    print(request.cookies)
    return 'Hello, World!'

We imported Flask and request modules, defined a Flask app and route for the root URL (‘/’). In the route function, we accessed request object properties such as method, headers, args, form, and cookies.

Properties of Flask Request Object

The Flask request object provides several properties that developers can use to access information about the incoming request. Some most used methods are:

1. Method

The method property contains the HTTP method used in the request, such as GET, POST, PUT, DELETE, etc.

@app.route('/')
def index():
    print(request.method)
    return 'Hello, World!'

2. Headers

The headers property contains a dictionary of HTTP headers sent in the request.

@app.route('/')
def index():
    print(request.headers)
    return 'Hello, World!'

3. Args

The args property contains a dictionary of URL parameters sent in the request.

@app.route('/')
def index():
    print(request.args)
    return 'Hello, World!'

4. Form

The form property contains a dictionary of form data sent in the request.

@app.route('/', methods=['POST'])
def index():
    print(request.form)
    return 'Hello, World!'

5. Cookies

The cookies property contains a dictionary of cookies sent in the request.

@app.route('/')
def index():
    print(request.cookies)
    return 'Hello, World!'

Methods of Flask Request Object

The Flask request object also provides several methods that developers can use to manipulate the incoming request data. Some most used methods

1. Get

The get method allows developers to retrieve a value from the request arguments or form data. It takes a key as an argument and returns the corresponding value.

@app.route('/')
def index():
    name = request.args.get('name')
    return f'Hello, {name}!'

2. Getlist

The getlist method allows developers to retrieve a list of values from the request arguments or form data. It takes a key as an argument and returns a list of values.

@app.route('/')
def index():
    fruits = request.args.getlist('fruit')
    return f'You selected: {", ".join(fruits)}'

3. Files

The files property contains a dictionary of files uploaded in the request. Each file is represented by a FileStorage object, which provides methods to access the file data, filename, content type, and other metadata.

@app.route('/', methods=['POST'])
def index():
    file = request.files['file']
    file.save('uploads/' + file.filename)
    return 'File uploaded successfully'

In the example above, we accessed the files property to retrieve a file uploaded in the request. We then saved the file to a directory called ‘uploads’ using the save method of the FileStorage object.

Handling HTTP Methods with Flask Request Object

In addition to the HTTP GET and POST methods, Flask also supports other HTTP methods, such as PUT, DELETE, and PATCH. The Flask request object provides a property called method that developers can use to check the HTTP method used in the request. Here’s an example of how to handle different HTTP methods in Flask:

@app.route('/', methods=['GET', 'POST', 'PUT', 'DELETE'])
def index():
    if request.method == 'GET':
        return 'This is a GET request'
    elif request.method == 'POST':
        return 'This is a POST request'
    elif request.method == 'PUT':
        return 'This is a PUT request'
    elif request.method == 'DELETE':
        return 'This is a DELETE request'

In the example above, we defined a route that handles multiple HTTP methods. We used an if-elif statement to check the HTTP method used in the request and returned a different response for each method.

Basic Flask Application

To get started with Flask, let’s create a simple “Hello, World!” application. Add the code to the python file named ‘app.py’

from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return 'Hello, World!'

In the code above, we created a new Flask application using the Flask class, and defined a single route that returns the string “Hello, World!” when the root URL is requested. We then started the application using the run method.

To run the application, save the file and run the following command in your terminal:

python app.py

Output

* Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Open a web browser and navigate to http://127.0.0.1:5000/, and you should see the “Hello, World!” message displayed in your browser.

Accessing Request Data with Flask Request Object

Now that we have a basic Flask application up and running, let’s explore how to access incoming request data using the Flask request object. The request object is an instance of the Request class provided by the Flask framework, and it contains information about the current request, such as the URL, HTTP method, headers, and request data.

To access the request object in a Flask application, we need to import it from the Flask module. Add the following line at the top of your app.py file:

from flask import Flask, request

Query Parameters

One common way to pass data in an HTTP request is through query parameters. Query parameters are key-value pairs that are appended to the end of a URL, separated by a question mark (?) and an ampersand (&) character.

To access query parameters in Flask, we can use the args property of the request object. The args property returns a dictionary-like object containing the query parameters

@app.route('/search')
def search():
    query = request.args.get('q')
    return f'Searching for: {query}'

In the example above, we defined a new route that handles requests to the /search URL. We used the args property to retrieve the value of the q query parameter, and returned a string containing the search query.

To test the /search route, open a web browser and navigate to http://127.0.0.1:5000/search?q=Flask, and you should see the message “Searching for: Flask” displayed in your browser.

Form Data

Another common way to pass data in an HTTP request is through form data. Form data is typically used in HTML forms to collect user input and submit it to a server.

To access form data in Flask, we can use the form property of the request object. The form property returns a dictionary-like object containing the form data.

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']
        return f'Logging in as: {username}'
    return '''
        <form method="post">
            <input type="text" name="username" placeholder="Username"><br>
            <input type="password" name="password" placeholder="Password"><br>
            <input type="submit" value="Log In">
        </form>
    '''

In the example above, we defined a new route that handles requests to the /login URL with both GET and POST methods. When a POST request is made, we used the form property to retrieve the values of the username and password fields from the form data, and returned a string containing the username. When a GET request is made, we returned an HTML form that collects the user’s login information.

To test the /login route, open a web browser and navigate to http://127.0.0.1:5000/login, enter a username and password in the form, and click the “Log In” button. You should see the message “Logging in as: [username]” displayed in your browser.

JSON Data

In addition to query parameters and form data, it’s also common to pass data in an HTTP request in JSON format. JSON (JavaScript Object Notation) is a lightweight data interchange format that is easy to read and write for both humans and machines.

To access JSON data in Flask, we can use the json property of the request object. The json property returns a dictionary-like object containing the JSON data.

@app.route('/users', methods=['POST'])
def create_user():
    user_data = request.json
    username = user_data['username']
    email = user_data['email']
    return f'Creating user: {username} ({email})'

In the example above, we defined a new route that handles POST requests to the /users URL. We used the json property to retrieve the JSON data from the request, and extracted the username and email fields from the JSON data. We then returned a string containing the username and email.

To test the /users route, you can use a tool like Postman to send a POST request to http://127.0.0.1:5000/users with a JSON payload containing the username and email fields:

{
    "username": "john",
    "email": "[email protected]"
}

Form data retrieval on the template:

In Flask, the request object is used to access the incoming HTTP request data. One common use case for the request object is to retrieve form data submitted by the user. Here’s an example of how to do that in a Flask template:

• In the Flask route function, retrieve the form data submitted by the user and pass it as a variable to the template:

from flask import Flask, render_template, request
#DataFlair
app = Flask(__name__)

@app.route('/', methods=['GET', 'POST'])
def index():
    if request.method == 'POST':
        name = request.form['name']
        email = request.form['email']
        return render_template('result.html', name=name, email=email)
    return render_template('index.html')

if __name__ == '__main__':
    app.run()

• In the HTML template, use the variables to display the form data:

<!DOCTYPE html>
<html>
<head>
    <title>Form Submission</title>
</head>
<body>
    <form method="post">
        <label for="name">Name:</label>
        <input type="text" name="name" id="name"><br><br>
        <label for="email">Email:</label>
        <input type="email" name="email" id="email"><br><br>
        <input type="submit" value="Submit">
    </form>
</body>
</html>

Attributes in Flask

In Flask, the request object represents the HTTP request sent by the client to the server. It contains information about the request, such as the request method, the URL, the headers, and any form data or JSON payload included in the request.

To write attributes to the Flask request object, you can use the request object’s setattr method. Here is an example:

from flask import Flask, request
#DataFlair
app = Flask(__name__)

@app.route('/example', methods=['POST'])
def example():
    request_data = request.get_json()  # parse JSON data from request body
    request_attrs = request_data.get('attrs', {})  # get the 'attrs' object from the JSON data, or use an empty dictionary if not present
    for key, value in request_attrs.items():
        setattr(request, key, value)  # set each key-value pair as an attribute on the request object
    return 'Success'

In this example, we define a Flask route that expects a POST request with JSON data in the request body. We first parse the JSON data using request.get_json(), then extract an object called attrs from the JSON data (or use an empty dictionary if it’s not present).

We then loop over the key-value pairs in the attrs object and use setattr to set each key-value pair as an attribute on the request object.

After the request attributes have been set, you can access them in any subsequent Flask route or function that handles the request. For example, if the attrs object contained a key-value pair of “foo”: “bar”, you could access the foo attribute on the request object like this:

#DataFlair
@app.route('/another-route')
def another_route():
    foo_value = request.foo
    # do something with foo_value
    return 'Success'

Proxies in Flask

In Flask, the request object is a proxy object that provides a convenient interface for accessing information about the client’s HTTP request. The request proxy object is created for each incoming request and is available throughout the request-handling cycle.

To write attributes to the Flask request proxy object, you can use the ProxyFix middleware provided by the werkzeug.middleware.proxy_fix module. This middleware is used to fix proxy setups that change the URL scheme, host, and port of incoming requests. Here is an example:

from werkzeug.middleware.proxy_fix import ProxyFix
from flask import Flask, request

app = Flask(__name__)
app.wsgi_app = ProxyFix(app.wsgi_app, x_proto=1, x_host=1)

@app.route('/example')
def example():
    request_attrs = {'foo': 'bar'}
    for key, value in request_attrs.items():
        setattr(request.environ['werkzeug.request'], key, value)
    foo_value = request.foo
    # do something with foo_value
    return 'Success'

In this example, we first import the ProxyFix middleware and wrap the app.wsgi_app attribute with it. We also pass x_proto=1 and x_host=1 to ProxyFix to indicate that we want the middleware to use the X-Forwarded-Proto and X-Forwarded-Host headers to determine the URL scheme and host of the request.

In the example route, we set the foo attribute of the request.environ[‘werkzeug.request’] object (which is the request proxy object) using setattr. We can then access this attribute using request.foo. Note that we need to use request.environ[‘werkzeug.request’] instead of just request to get the actual proxy object.

Callbacks and Error in Flask

In Flask, you can also use the request object to pass data to callbacks and error handlers.

To pass data to a callback function, you can use the callback_kwargs parameter when registering the route. Here is an example:

#DataFlair
from flask import Flask, request

app = Flask(__name__)

@app.route('/example', methods=['POST'], endpoint='example_endpoint')
def example():
    request_data = request.get_json()
    request_attrs = request_data.get('attrs', {})
    for key, value in request_attrs.items():
        setattr(request, key, value)
    return 'Success'

def callback_func():
    foo_value = request.foo
    # do something with foo_value

app.add_url_rule('/another-route', endpoint='another_endpoint', view_func=callback_func, methods=['GET'], callback_kwargs={'foo': 'bar'})

In this example, we define a Flask route example that sets request attributes, and a callback function callback_func that retrieves the foo attribute from the request object.

When registering the route for callback_func with app.add_url_rule, we pass callback_kwargs={‘foo’: ‘bar’} to specify the value of the foo attribute. This value will be available as an argument to callback_func.

To pass data to an error handler, you can use the app.handle_exception method. Here is an example:

#DataFlair
from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route('/example', methods=['POST'])
def example():
    request_data = request.get_json()
    request_attrs = request_data.get('attrs', {})
    for key, value in request_attrs.items():
        setattr(request, key, value)
    return 'Success'

@app.errorhandler(Exception)
def handle_exception(e):
    error_message = str(e)
    error_code = getattr(request, 'error_code', 500)
    return jsonify({'error_message': error_message, 'error_code': error_code}), error_code

@app.route('/error-example')
def error_example():
    raise Exception('An error occurred', 400)

with app.app_context():
    app.handle_exception = handle_exception

In this example, we define a Flask route example that sets request attributes, and an error handler handle_exception that retrieves the error_code attribute from the request object (defaulting to 500 if it’s not present) and returns a JSON response with the error message and code.

To register the error handler with the Flask app, we use app.handle_exception = handle_exception within a with app.app_context() block.

In the error-example route, we raise an exception with an error message and code of 400. The error handler will catch this exception and return a JSON response with the error message and code.

Conclusion

In this article, we explored the Flask request object, and how to use it to access and manipulate incoming request data in our web applications. We looked at how to access query parameters, form data, and JSON data using the args, form, and json properties of the request object. With the Flask request object, we can build powerful and flexible web applications that can handle a wide range of incoming request data.