Truediv | Marcel Blijleven

I’m a big fan of the way the / operator can be used to ‘build’ Path objects. For example, Path("foo") / "bar" becomes foo/bar. So what makes this possible?

Turns out it’s the __truediv__ method. This method allows you to modify the behaviour of a class when the / operator is used. This opens up all sorts of cool things, for example building an url using the builtin urljoin function.

In the following example I use Pydantic’s RootModel to create a FancyUrl model that calls the urljoin function inside the __truediv__ method and returns the output. I then use this in a ‘Settings’ object to demonstrate a use-case.

from urllib.parse import urljoin
from pydantic import RootModel
from pydantic_settings import BaseSettings


class FancyUrl(RootModel):
    root: str

    def __truediv__(self, other: str) -> str:
        return urljoin(self.root, other)

    def __str__(self) -> str:
        return self.root


class Settings(BaseSettings):
    blog: FancyUrl


settings = Settings(blog="https://marcelblijleven.com")

# This prints https://marcelblijleven.com
print(settings.blog)
# This prints https://marcelblijleven.com/blog/truediv
print(settings.blog / "blog/truediv")

This is already quite nice, but what if you want to add more segments? If you run settings.blog / "blog" / "foo" you’ll be presented with an error:

TypeError: unsupported operand type(s) for /: 'str' and 'str'

This is because we return a str and not a FancyUrl. So let’s improve the __truediv__ method a bit.

...
from typing import Self  # This import is added
...

class FancyUrl(RootModel):
    root: str

    def __truediv__(self, other: str) -> Self:
        # We now set self.root here
        self.root = urljoin(self.root, other)
        # And return self
        return self

    def __str__(self) -> str:
        return self.root

...

This solves the issue and lets you chain the / operator on your new FancyUrl!

Tags:

python

code