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Create CLIs with classes and type hints.

Project description

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Cliar is yet another Python package to create commandline interfaces. It focuses on simplicity, extensibility, and testability:

  • Creating a CLI is as simple as creating subclassing cliar.Cliar.
  • Extending a CLI is as simple as subclassing from the base CLI class.
  • Testing a CLI is as simple as unittesting a class.

Cliar's mission is to let the programmer focus on the business logic instead of building an interface for it. At the same time, Cliar doesn't want to stand in the programmer's way, so it provides means to customize the generated CLI.


pip install cliar

Cliar runs with Python 3.6+ on Windows, Linux, and Mac. There are no dependencies outside Python's standard library.

Basic Usage

Let's create a calculator app. Version 1.0.0 will implement only addition of two real numbers.

Here's how you do it with Cliar:

from cliar import Cliar

class Calculator(Cliar):
    '''Calculator app.'''

    def add(self, x: float, y: float):
        '''Add two real numbers.'''

        print(f'The sum of {x} and {y} is {x+y}.')

if __name__ == '__main__':

Save this code as and run it with different inputs:

$ python run add 12 34
The sum of 12.0 and 34.0 is 46.0.

$ python run foo bar
usage: add [-h] x y add: error: argument x: invalid float value: 'foo'

$ python run -h
usage: [-h] {add} ...

Calculator app.

optional arguments:
  -h, --help  show this help message and exit

  {add}       Available commands:
    add       Add two real numbers.

$ python add -h
usage: add [-h] x y

Add two real numbers.

positional arguments:

optional arguments:
  -h, --help  show this help message and exit

There are a few things to note in the code above:

  • It's a regular Python class with a regular Python method. You don't need to learn any new syntax to use Cliar.
  • The add method was converted into add command, and its positional params were converted into positional commandline args.
  • We don't convert x or y to float or handle any potential conversion errors in the add body. Instead, we treat x and y as if they were already guaranteed to be floats. That's because Cliar does the validation and conversion for us, using the information from add's type hints. Note how invalid input doesn't even reach your code.
  • The --help and -h flags are added automatically and the help messages were generated from the docstrings.

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