3.3 Using Browser from Python

To create a custom Python library that uses the same Browser instance as your Robot Framework tests, you can fetch the already-imported Browser library instance from Robot Framework.

Important: avoid doing this in __init__.

Robot Framework tooling often instantiates (and introspects) libraries when generating keyword documentation and editor features. If your __init__ touches external resources (for example, expects a Browser/Playwright connection to exist), these tools can break.

This is why a lazily-evaluated cached_property is a good fit:

• LibDoc initializes the class to generate docs; if __init__ tries to access external resources, doc generation can fail.
• RobotCode (code completion) also uses LibDoc-style introspection; __init__ gets executed just to discover keywords.
• Keeping __init__ lightweight avoids unnecessary work when Robot Framework creates multiple instances even if no keyword is ever executed.

cached_property (from Python's standard library functools) computes the value once per instance on first access and then caches it on the object. Later accesses return the cached value.

@library
class CarConfigLibrary:
    ROBOT_LIBRARY_SCOPE = "GLOBAL"
    ROBOT_LIBRARY_VERSION = VERSION

    @cached_property
    def b(self) -> Browser:
        """Return the already-imported Browser library instance.

        Resolved lazily so LibDoc/RobotCode introspection does not require Browser/Playwright to be available.
        """
        try:
            return BuiltIn().get_library_instance("Browser")
        except RuntimeError:
            raise ImportError("You have to import the library 'Browser' as well.")

With this property (self.b), you can then access all Browser keywords directly.

Example:

    @keyword
    def login_user(self, user: str, password: str):
        """Login a User"""
        self.b.type_text("#input_username", user)
        self.b.type_text("#input_password", password)
        self.b.click("#button_login")

See the example files.

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