Adventures in Machine Learning

Mastering URL Construction in Python: urljoin() and posixpathjoin()

Joining URLs with urljoin() method

Are you finding it challenging to join URLs to create a unique address? You’re not alone.

The good news is that there’s an effortless and efficient way to do it. The urljoin() method is the key function you need to master to accomplish the task effortlessly.

Using urljoin() to Join a Base URL with Another URL

The urljoin() method is a member of the Python standard library’s urllib.parse module. It allows you to join a base URL and another URL to create a complete URL.

The function can handle both absolute and relative URLs. The syntax for using the method is as follows:

“`urljoin(base_url, url_to_join)“`

The base_url is the primary URL used when constructing a URL, while the url_to_join is the secondary address to be added to the base.

Joining URL Path Components When Constructing a URL

URL path components are an essential part of constructing a URL. If you’re not careful, you may forget to include even just one section of the path, creating a broken URL or even an entirely different file from the one intended.

Fortunately, the urljoin() method can help ensure that the different path components are correctly joined and create a valid URL. If you’re working with a URL that has distinct path components, you can use the join() method provided by Python’s urllib.parse module.

The join() method automatically eliminates any duplicate slashes, as well as any trailing slashes that may occur, creating a URL that’s neat and tidy. The syntax is as follows:

“`urlparse.urljoin(‘’, ‘/path2/file.html’)“`

Example of Using urljoin() Method

Forward Slashes and URL Components

One feature of the urljoin() method to note is that the function takes into account the presence or absence of forward slashes in the URL components. If the base_url does not end with a forward slash (i.e., /), and the url_to_join does not start with one, then the urljoin() will join the two URLs without adding an extra forward slash between them.

For instance, the following code joins two URLs without adding the forward slash:

“`urljoin(“”, “page.html”)“`

If the base_url ends with a forward slash, and the url_to_join doesn’t start with one, the urljoin() function will add an extra forward slash between the two URLs. For instance, the following code joins two URLs with an added forward slash:

“`urljoin(“”, “/directory/file.html”)“`

Assumed Root When the Second Component Starts With a Forward Slash

When the url_to_join begins with a forward slash, the urljoin() method ignores any base_url and assumes it to be the root directory. The resulting URL will consist only of the domain name and the second URL component.

This feature is especially useful when creating an absolute URL. For instance:

“`urljoin(“”, “/images/picture.png”)“`



The root directory for the second URL component (/images/picture.png) has assumed that the base_url is the root and has only used the domain name when constructing the new URL.


Using the urljoin() method provides an effortless and more efficient way of constructing URLs. It takes care of the task of joining various URL components, dealing with forward slashes and assuming roots in a seamless process. Understanding the function’s features and syntax will help to ensure that your URLs are accurate, functional and built with ease.

Joining URL Path Components with Posixpath.join()

When constructing URLs, it’s not uncommon to have to join multiple path components to create a valid address. While the urljoin() method is great for combining URLs, you may need to use the posixpath.join() method when working with path components.

Here, we’ll take a look at how to use this function to combine URL path components, its syntax, and unique features. Using posixpath.join() Method to Join URL Path Components

The posixpath module provides a function called join() that can be used to combine or join multiple path components together, including URLs, paths, and subdirectories.

This join method supports both Windows and Unix-style paths.

Here’s an example:

“`from posixpath import join

url = ‘’

folder = ‘images’

filename = ‘picture.png’

full_url = join(url, folder, filename)


This code uses the join() function to construct a complete URL, by joining together the various path components.

The final output of this code will be:


The join() function completes this task by joining all parts together, and automatically takes care of removing any double slashes between the segments. Posixpath.join() Method Can Be Passed More Than 2 Paths

The posixpath.join() function can also be passed more than two paths at once.

This is useful when creating URLs for subdirectories or nested folders since consecutive calls to posixpath.join() would create a longer, more complicated program.

“`from posixpath import join

url = ‘’

parent_folder = ‘media’

sub_folder = ‘images’

sub_folder2 = ‘car_images’

filename = ‘mustang.jpg’

full_url = join(url, parent_folder, sub_folder, sub_folder2, filename)


Here, we’re passing multiple strings to join together to create an entire path that consists of a combination of URL path components.

The output of the above code will be:


This approach makes it much easier to construct complex URLs with numerous subdirectories and files, without the need to make dozens of calls to the join() method.

Related Tutorials

To learn more about joining URL path components or to become more familiar with other Python Web Development resources, here are some related tutorials you may find useful:

1. Documentation – The official Python documentation is always a good resource for information on modules, functions, and methods, such as urljoin() and posixpath.

Visit 2.

SoloLearn – SoloLearn provides a comprehensive learning app for Python, including topics on web development using Python, and specifically URL construction/cleaning. Visit

3. Udemy – Udemy offers various courses on Python web development covering Flask, REST APIs, Django Web Framework, and more.

Visit 4.

RealPython – RealPython is an online platform that offers numerous Python tutorials, including URL manipulation, as well as web development resources. Visit, or


Joining URL path components is a fundamental task in Python web development. The urljoin() method and posixpath.join() function are both effective tools to combine URL path components, whether you’re working with multiple URLs, subdirectories, or files.

Understanding how to use these functions is essential to create URLs that are valid, functional, and build with ease. With the added resources provided, you have everything you need to become more proficient at Python Web Development.

In summary, constructing valid and functional URLs is a fundamental aspect of Python web development. The urljoin() and posixpath.join() functions are essential tools to join URL components and create URLs efficiently and accurately.

Understanding these functions’ features and syntax will make it easy to combine different path components, including multiple URLs, subdirectories, and files. With the additional resources provided, developers can continue to enhance their Python web development skills and create URLs that are efficient, robust and functional.

Overall, mastering these functions adds a vital skill to your arsenal, making you more productive in any web development project.

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