Introduction

Flask is one of the most popular Python web development frameworks. It's a lightweight web framework, yet it offers a variety of built-in methods that can be used for hassle-free deployment of efficient web applications.

In this guide, we will get the IP address of the user who visits the web application created using Flask.

We'll create a simple REST API that handles the incoming requests to the / endpoint, returning the IP address of the user as the response.

Creating a Basic Web App Using Flask

Create a new Flask project for this tutorial. We'll create a basic app that returns "Hello World" with requests to the / endpoint:

from flask import Flask

# Creating the instance of the class Flask
app = Flask(__name__)

# Using the decorator to create the URL for the web application
@app.route('/')
# The function will return the information displayed on the webpage
def hello_world():
    return '<h1> Hello World</h1>'

# Run the application
if __name__ == '__main__':
    app.run(debug=True)

Now that we have our app set up, let's collect the IP addresses associated with a user's request.

How to Find the IP Address Of a User in Flask?

Whenever a client requests a page - they send an HTTP GET request, with a certain payload. Amongst other information - their distinctive IP address is included. In Flask - every route has access to the request variable, which represents the incoming request from the user. From this request, we can extract various elements - and the IP address is denoted as the remote_addr property:

@app.route('/')
def hello_world():
    ip_addr = request.remote_addr
    return '</code><h1><code> Your IP address is:' + ip_addr

</code></h1></pre>

We can also get the remote address through the request context's environment. The <code>environ</code> dictionary of the <code>request</code> object holds various keys and their respective values, pertaining to the request. The <code>REMOTE_ADDR</code> is one of the server variables (keys) that is mapped to the IP address of the client or the server:

@app.route('/client') def client(): ipaddr = request.environ['REMOTEADDR'] return '

Your IP address is:' + ip_addr

But the above two options won't work if your user is making a request behind a proxy. In that case we have to check the headers of the request. In particular, we're looking for the HTTP_X_FORWARDED_FOR header:

@app.route('/proxy-client')
def proxy_client():
    ip_addr = request.environ['HTTP_X_FORWARDED_FOR']
    return '</code><h1><code> Your IP address is:' + ip_addr

</code></h1></pre>

Now, even this approach would not work if the header is not set. So a common strategy is to use the <code>get()</code> method so that if the header is not set, we can default to the remote address:

@app.route('/proxy-client') def proxyclient(): ipaddr = request.environ.get('HTTPXFORWARDEDFOR', request.remoteaddr) return '

Your IP address is:' + ip_addr

Note: Trying to get a value from a non-existent key returns None. The get() method of the dict class allows you to set a default value to be used if get() fails to find a key. If HTTP_X_FORWARDED_FOR is None, the request.remote_addr value is used instead.

        With these in mind, we can choose from any of the following three approaches to get the IP address of a user, via their incoming request:

```

from flask import Flask, request

app = Flask(name)

@app.route('/') def helloworld(): ipaddr = request.remoteaddr return '

Your IP address is:' + ipaddr

@app.route('/client') def client(): ipaddr = request.environ['REMOTEADDR'] return '

Your IP address is:' + ip_addr

@app.route('/client') def proxyclient(): ipaddr = request.environ.get('HTTPXFORWARDEDFOR', request.remoteaddr) return '

Your IP address is:' + ip_addr if __name__ == '__main__': app.run(debug=True)

Conclusion

In this article, we learned three different methods to get the IP address of a user. We access the remote address directly with request.remote_addr, through the REMOTE_ADDR key from request.environ, and in the cases where the user is using a proxy we should check the HTTP_X_FORWARDED_FOR key of request.environ.

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