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How to check if a string is a valid URL in Python

How to check if a string is a valid URL in Python.

Here's a step-by-step tutorial on how to check if a string is a valid URL in Python:

Step 1: Import the necessary modules​

To perform URL validation in Python, you will need to import the re module, which provides support for regular expressions. You can import it using the following line of code:

import re

Step 2: Define a function to check if a string is a valid URL​

Create a function called is_valid_url that takes a string as input and returns a boolean value indicating whether the string is a valid URL. Inside the function, you can use regular expressions to validate the URL. Here's an example implementation:

def is_valid_url(url):
    # Regular expression pattern to match a valid URL
    pattern = re.compile(
        r'^https?://'  # http:// or https://
        r'([a-z0-9.-]+)'  # domain name
        r'(\.[a-z]{2,4})'  # dot-something
        r'(/[a-zA-Z0-9%._-]+)*'  # path
        r'(\?[a-zA-Z0-9&=]+)*'  # query string
        r'(#[a-zA-Z0-9_-]+)?$'  # fragment identifier
        , re.IGNORECASE)
    
    # Use the pattern to match the URL
    match = re.match(pattern, url)
    
    # Return True if the URL is valid, otherwise False
    return bool(match)

Let's break down the regular expression pattern used in this example:

  • ^https?://: Matches the start of the string followed by http:// or https://.
  • ([a-z0-9.-]+): Matches the domain name, which can consist of lowercase letters, numbers, dots, and hyphens.
  • (\.[a-z]{2,4}): Matches the top-level domain (e.g., .com, .org). It allows 2 to 4 lowercase letters.
  • (/[a-zA-Z0-9%._-]+)*: Matches the path, which can include alphanumeric characters, percent-encoded characters, dots, underscores, and hyphens. The path can be optional and can contain multiple segments separated by slashes.
  • (\?[a-zA-Z0-9&=]+)*: Matches the query string, which can include alphanumeric characters, ampersands, and equals signs. The query string can be optional.
  • (#[a-zA-Z0-9_-]+)?$: Matches the fragment identifier (e.g., #section). The fragment identifier can be optional.

Step 3: Test the function with example URLs​

You can now test the is_valid_url function with different URLs to see if it correctly identifies them as valid or invalid. Here are a few examples:

# Test the function with example URLs
print(is_valid_url("https://www.example.com"))  # True
print(is_valid_url("http://example.com"))  # True
print(is_valid_url("www.example.com"))  # False
print(is_valid_url("example.com"))  # False

In this example, the first two URLs are valid and should return True, while the last two URLs are invalid and should return False.

That's it! You now have a function that can check if a string is a valid URL in Python.