Booleans

Booleans are also valid types on Platitudes CLIs, however, they behave differently to other types. Booleans always are expressed and behave as optional parameters but in contrast to normal optional values it is mandatory to pass them unless a default argument has been given to them in the function signature. That is:

1. There name is prefixed with -- on the CLI;
2. They can be provided at any position;
3. The don't count towards the positional arguments even if they don't have a default value;

In addition to the rules above Platitudes generates 2 variants optional parameters for each boolean according to the rules of argparse.BooleanOptionalAction. Here are some examples to make all of this clearer:

Automatic bool option generation

For each bool two variants representing True/False are generated. In the example below these would be: - --is-rainy - --no-is-rainy

import platitudes as pl


def weather(is_rainy: bool):
    print(f"Is it rainy: {is_rainy}")


pl.run(weather)

❯ python bool_01.py --is-rainy        
Is it rainy: True

❯ python bool_01.py --no-is-rainy        
Is it rainy: False

Booleans without a default are mandatory

Despite looking like optional parameters (they are prefixed with --) if a default is not provided they must be passed. Using the same example as above this is what happens when no default is provided:

❯ python bool_01.py              
usage: bool.py [-h] --is-rainy | --no-is-rainy
bool.py: error: the following arguments are required: --is-rainy/--no-is-rainy

Booleans with a default are not mandatory

Of course if a default is provided then we don't need to explicitly pass it.

import platitudes as pl


def weather(is_rainy: bool = False):
    print(f"Is it rainy: {is_rainy}")


pl.run(weather)

❯ python bool_02.py
Is it rainy: False

But keep in mind that the --is-rainy variant still represents True! And the --no-xxx variant represents False regardless of the default value.

❯ python bool_02.py  --no-is-rainy
Is it rainy: False

❯ python bool_02.py  --is-rainy
Is it rainy: True

Booleans don't count towards the positional arguments

Even when no default is provided they are still optional in the sense that they can be specified at any location and don't count towards the positional arguments.

import platitudes as pl


# is_rainy should nominally behave as positional but bools are special
def weather(cloud_cover: float, is_rainy: bool, humidity: float, pressure: float = 1.0):
    print(f"The cloud cover is: {cloud_cover}%")
    print(f"Is it rainy: {is_rainy}")
    print(f"The humidity is: {humidity}%")
    print(f"The pressure is {pressure} atm")


pl.run(weather)

And all the following work despite is_rainy being the second argument to the function and not having a default value.

❯ python bool_03.py 10 20 --is-rainy
The cloud cover is: 10.0%
Is it rainy: True
The humidity is: 20.0%
The pressure is 1.0 atm

❯ python bool_03.py 10 20 --pressure 1.1 --is-rainy 
The cloud cover is: 10.0%
Is it rainy: True
The humidity is: 20.0%
The pressure is 1.1 atm