Frequently asked questions for LightningCLI¶
What does CLI stand for?¶
CLI is short for command line interface. This means it is a tool intended to be run from a terminal, similar to commands
What is a yaml config file?¶
A YAML is a standard for configuration files used to describe parameters for sections of a program. It is a common tool in engineering and has recently started to gain popularity in machine learning. An example of a YAML file is the following:
# file.yaml car: max_speed:100 max_passengers:2 plane: fuel_capacity: 50 class_3: option_1: 'x' option_2: 'y'
If you are unfamiliar with YAML, the short introduction at realpython.com#yaml-syntax might be a good starting point.
What is a subcommand?¶
A subcommand is what is the action the LightningCLI applies to the script:
python main.py [subcommand]
See the Potential subcommands with:
python main.py --help
... fit Runs the full optimization routine. validate Perform one evaluation epoch over the validation set. test Perform one evaluation epoch over the test set. predict Run inference on your data. tune Runs routines to tune hyperparameters before training.
use a subcommand as follows:
python main.py fit python main.py test
What is the relation between LightningCLI and argparse?¶
LightningCLI makes use of jsonargparse
which is an extension of argparse. Due to this,
LightningCLI follows the same arguments style as many POSIX command line tools. Long
options are prefixed with two dashes and its corresponding values are separated by space or an equal sign, as
--option=value. Command line options are parsed from left to right, therefore if a setting appears
multiple times, the value most to the right will override the previous ones.
What is the override order of LightningCLI?¶
The final configuration of CLIs implemented with
LightningCLI can depend on default
config files (if defined), environment variables (if enabled) and command line arguments. The override order between
these is the following:
Defaults defined in the source code.
Existing default config files in the order defined in
Entire config environment variable, e.g.
Individual argument environment variables, e.g.
Command line arguments in order left to right (might include config files).
How do I troubleshoot a CLI?¶
The standard behavior for CLIs, when they fail, is to terminate the process with a non-zero exit code and a short
message to hint the user about the cause. This is problematic while developing the CLI since there is no information to
track down the root of the problem. To troubleshoot set the environment variable
JSONARGPARSE_DEBUG to any value
before running the CLI:
export JSONARGPARSE_DEBUG=true python main.py fit
When asking about problems and reporting issues, please set the
JSONARGPARSE_DEBUG and include the stack trace
in your description. With this, users are more likely to help identify the cause without needing to create a