What is urls.py file in Django?

URLs.py file is an essential component of a Django web application. Django is a high-level Python web framework that encourages rapid development and clean, pragmatic design, and the urls.py file plays a critical role in routing and handling requests in Django.

In Django, whenever a user makes a request for a page from your web application, Django controller takes over to look for the appropriate view. The urls.py file is where Django stores the list of mappings between URLs and views. This set of mappings is written as a Python module and is the basic element of Django’s URL handling mechanism.

Here’s an example of what urls.py might look like:

```
from django.urls import path

from . import views

urlpatterns = [ path(‘articles/2003/’, views.special_case_2003), path(‘articles//’, views.year_archive), path(‘articles///’, views.month_archive), path(‘articles////’, views.article_detail),
]
```
In this example, each call to the `path` function corresponds to a pattern for a URL. When Django evaluates these, it starts at the top and goes down the list sequentially until it finds one that matches.

Each `path` function has at least two required arguments: a route and a view. The route is a string that contains a URL pattern. When processing a request, Django starts at the first pattern in urlpatterns and makes its way down the list, comparing the requested URL against each pattern until it finds one that matches.

When one pattern is found that matches, Django imports and calls the given view, which is a Python function (or a class-based view). The view gets passed the following arguments:

1. An instance of `HttpRequest`.

1. If the matched route resulted in captured arguments, those are passed as keyword arguments.

1. The remaining keyword arguments are passed from the optional `kwargs` argument to `path()`.

The `views.py` file then processes the request and sends a HTTP response back to the user’s web browser.

To put it simply, the urls.py file in Django is like a table of contents for your Django project. It’s a map that tells Django which code to run for each URL pattern.

These explanations are based on the information from the Django’s official documentation (https://docs.djangoproject.com/en/3.2/topics/http/urls/), which is the most comprehensive and reliable source on Django.

In addition to official Django documentation, other educational sources such as Mozilla Developer Network (https://developer.mozilla.org/en-US/docs/Learn/Server-side/Django/skeleton\_website) and Real Python (https://realpython.com/tutorials/django/) also provide detailed explanations and examples of Django’s urls.py file, making them useful resources for learning Django’s URL dispatching mechanism.