CLI Rack - Lightweight set of tools for building pretty-looking CLI applications in Python

python, cli, terminal, modular, oop
pip install cli-rack==1.0.4


CLI Rack Cover Picture

CLI Rack

Lightweight set of tools for creating pretty-looking CLI applications in Python. This library tends to simplify and unify the approach to structuring CLI related code. At the moment it covers:

  • Managing terminal output - verbosity levels, colored output, logger configuration
  • Parsing arguments
  • Modular application design - each module could extend argument parser with own command
  • Modules discovery - scanning packages to find cli extension modules
  • Module availability support - module might declare a method to verify if environment is suitable (e.g. all dependencies are present). If not, module will be automatically excluded from CLI interface
  • Sync and Async execution managers
  • Loading external components
  • Installing optional dependencies


CLI output

The module provides built-in methods to output information for the end user. It is configured to pint direct informational messages, errors and warnings to the stderr and execution result to stdout.

The functionality is available via special object called CLI. Consider the following example:

from cli_rack import CLI


CLI.print_info("This is just a message to user")
CLI.print_warn("This is a warning")
CLI.print_error("This is an error message")
CLI.print_error(ValueError("This is an exception"))
CLI.print_data("This text comes to STDOUT, not STDERR")

CLI.setup() must be invoked in the very beginning of the program as it determines terminal capabilities and configures logger, filters and formatters. It is also possible to configure verbosity level on this stage. See Section Verbosity configuration for details.

Methods CLI.print_* have very similar interface and are designed for printing information of specific type. It is highly important to avoid simple built-in print function and use CLI.print_* methods instead as it allows to keep output clean, consistent and well formatted. Also, verbosity control won't work for any data written directly into output stream. It is also possible to override formatting options for individual message see Section Formatting capabilities for more details.

CLI.print_info(msg: str, style: Optional[ansi.AnsiCodeType] = None)

Verbosity configuration


Debug mode


Formatting capabilities



Preconfigured logger


Streamlined interface for tuning configuration


Loading external libraries

If you are building modular application you might want to allow your app with external components loaded from remote repository/server/registry. cli_rack.loader package streamlines development of this feature.

The example below illustrates the main idea:

from cli_rack import CLI, ansi
from cli_rack.loader import LoaderRegistry

CLI.print_info("Loading module using loader registry\n", ansi.Mod.BOLD)

LoaderRegistry.target_dir = "generated"

resource_meta = LoaderRegistry.load("github://logicify/healthcheckbot")

Here we configure loader to put downloaded modules into generated folder. Then ask to download module using the following resource locator github://logicify/healthcheckbot. LoaderRegistry tries to find loader capable to handle this type of locator (built-in GithubLoader in this case) and passes control to particular loader.

Loader will check if the local copy of the package is already present and it is up to date. If this is the case nothing will be downloaded. Otherwise, it will download data and put it under target_dir.

The data in the remote location might have different directory layout and it is highly likely you don't need file from the root, but rather interested in some subdirectory. For this purpose you could create a path_resolver function like this:

import os
from cli_rack.loader import LoadedDataMeta, InvalidPackageStructure, LoaderRegistry

def packages_dir_resolver(meta: LoadedDataMeta) -> str:
    if os.path.isdir(os.path.join(meta.path, "packages")):
        return "packages"
    raise InvalidPackageStructure(meta, "Folder \"packages\" must be present in directory root")

LoaderRegistry.target_dir = "generated"
resource_meta = LoaderRegistry.load("github://corvis/esphome-packages", packages_dir_resolver)





Extending cli_rack.loader with custom loader

It is pretty trivial to implement custom loader to fetch data from other sources (e.g. your proprietary company NAS):

  1. Implement cli_rack.loader.BaseLocatorDef and cli_rack.loader.BaseLoader (you might want to use GithubLoader as an example).
  2. Register it in LoaderRegistry:
from cli_rack.loader import LoaderRegistry

Modular application architecture

* Global options
* Commands
* Params
* Dynamic available commands discovery
* Commands availability
* Automatic dependencies installation


  • Dmitry Berezovsky, author


This module is licensed under MIT. This means you are free to use it in commercial projects.

The MIT license clearly explains that there is no warranty for this free software. Please see the included LICENSE file for details.