• Docs >
  • Handle Lightning App exceptions

Handle Lightning App exceptions

Audience: Users who want to make Lightning Apps more robust to potential issues.

Level: Advanced

What handling Lightning App exceptions does for you

Imagine you are creating a Lightning App (App) where your team can launch model training by providing their own Github Repo any time they want.

As the App admin, you don’t want the App to go down if their code has a bug and breaks.

Instead, you would like the LightningWork (Work) to capture the exception and present the issue to users.

Configure exception handling

The LightningWork (Work) accepts an argument raise_exception which is True by default. This aligns with Python default behaviors.

However, for the user case stated in the previous section, we want to capture the Work exceptions. This is done by providing raise_exception=False to the work __init__ method.

import lightning as L

MyCustomWork(raise_exception=False)  # <== HERE: The exception is captured.

# Default behavior
MyCustomWork(raise_exception=True)  # <== HERE: The exception is raised within the flow and terminates the app

And you can customize this behavior by overriding the on_exception hook to the Work.

import lightning as L

class MyCustomWork(L.LightningWork):

    def on_exception(self, exception: Exception):
        # do something when an exception is triggered.

Exception handling example

This is the pseudo-code for the application described above.

import lightning as L

class RootFlow(L.LightningFlow):
    def __init__(self):
        self.user_jobs = L.structures.Dict()
        self.requested_jobs = []

    def run(self):
        for request in self.requested_jobs:
            job_id = request["id"]
            if job_id not in self.user_jobs:
                # Note: The `GithubRepoLauncher` doesn't exist yet.
                self.user_jobs[job_id] = GithubRepoLauncher(
                    raise_exception=False, # <== HERE: The exception is captured.

            if self.user_jobs[job_id].status.stage == "failed" and "printed" not in request:
                print(self.user_jobs[job_id].status) # <== HERE: Print the user exception.
                request["printed"] = True

© Copyright Copyright (c) 2021-2022, Lightning-AI et al...

Built with Sphinx using a theme provided by Read the Docs.