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Project Notes

Simple Command Line Tools with begins

Using the begins library to write command line scripts without all the cruft.

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Notes

The begins library replaces conventional argparse/main function pattern with a simple decorator. I found this in 20 Python Libraries You Aren’t Using (But Should), from which I’ve basically snaffled this example.

The following are functionally equivalent. First the traditional way:

import argparse

def add(a, b):
    return a + b

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description="Add two numbers")
    parser.add_argument('-a', help='First value', type=float, default=0)
    parser.add_argument('-b', help='Second value', type=float, default=0)
    args = parser.parse_args()
    print(add(args.a, args.b))

And now using begins (python3 syntax):

import begin

@begin.start(auto_convert=True)
def add(a: 'First value' = 0.0, b: 'Second value' = 0.0):
    """ Add two numbers """
    print(a + b)

Setup

Use the requirements.txt to install begins:

$ pip install -r requirements.txt

The examples that follow use both python 2 and python 3. the begins library needs to installed for both.

Running the Examples

add.py is the conventional approach, with argparse and an explicit main section:

$ python add.py -h
usage: add.py [-h] [-a A] [-b B]

Add two numbers

optional arguments:
  -h, --help  show this help message and exit
  -a A        First value
  -b B        Second value

$ python add.py -a 3 -b 4
7.0

add_with_begins.py uses begins and python 2 compatible syntax:

$ python add_with_begins.py -h
usage: add_with_begins.py [-h] [--a A] [--b B]

Add two numbers

optional arguments:
  -h, --help   show this help message and exit
  --a A, -a A  (default: 0.0)
  --b B, -b B  (default: 0.0)

$ python add_with_begins.py -a 3 -b 4
7.0

add_with_begins3.py uses begins and python 3 compatible syntax:

$ python3 add_with_begins3.py -h
usage: add_with_begins3.py [-h] [--a A] [--b B]

Add two numbers

optional arguments:
  -h, --help   show this help message and exit
  --a A, -a A  First value (default: 0.0)
  --b B, -b B  Second value (default: 0.0)

$ python3 add_with_begins3.py -a 3 -b 4
7.0

Credits and References

About LCK#76 pythonCLI
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This page is a web-friendly rendering of my project notes shared in the LittleCodingKata GitHub repository.

LittleCodingKata is my collection of programming exercises, research and code toys broadly spanning things that relate to programming and software development (languages, frameworks and tools).

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