predica

Predicates for use in higher-order functions.

Tasks

• Keep API as simple as possible. For instance, P.* to access all predicates.
• Predicates or P should only evalaute as predicates or return predicates.
• Extend P.and_ and P.or to take containers of predicates.
• Improve usage example.

Installation

pip install predica

Usage

Let's illustrate usage with three examples, gradually improving the composability of the code:

Simple example -

from predica import P  # you can import `Predicates` too

ages = [1, 10, 100, 1000, '1']

# before
ages_no_str = list(filter(lambda x: not isinstance(x, str), ages)) # [1, 10, 100, 1000]

# after
new_ages_no_str = list(filter(P.not_instanceof(str), ages)) # [1, 10, 100, 1000]

Suppose you have a pre-existing function is_str -

def is_str(x: str) -> bool:
    return isinstance(x, str)

# before
ages_no_str = list(filter(lambda x: not is_str(x), ages))  # [1, 10, 100, 1000]

# after
new_ages_no_str = list(filter(P.negation(is_str), ages))  # [1, 10, 100, 1000]

IMO this works best with returns library or result library, following is example with Result from returns.result -

from returns.result import Result
from functools import partial

ages = Result.from_value([1, 10, 100, 1000, '1'])

ages.map(partial(filter, P.not_instanceof(str))).map(list)  # Success([1, 10, 100, 1000])
# or
ages.map(partial(filter, P.negation(is_str))).map(list)  # Success([1, 10, 100, 1000])

Much better 😮