A callable dictionary useful for functional programming

callable_dict.py

from typing import Optional, Hashable, TypeVar

class CallableDict(dict):
    V = TypeVar('V')
    
    """ A callable dictionary useful for functional programming """
    def __call__(self, key: Hashable, default: Optional[V]=None) -> Optional[V]:
        return self.get(key, default)


label_nums = CallableDict({
    'app.launch': 0, 
    'app.exit': 1,
    'app.pause': 2,
    'app.resume': 3,
})

print(label_nums['app.pause'])

print(list(map(label_nums, [
    'app.launch', 'app.pause', 'app.resume', 'app.exit', 'app.launch', 'app.pause', 'app.exit', 
    'app.launch', 'app.exit',
])))

Python has a native syntax to do functional processing on anything: list comprehensions.

    print(list(map(label_nums, [
        'app.launch', 'app.pause', 'app.resume', 'app.exit', 'app.launch', 'app.pause', 'app.exit', 
        'app.launch', 'app.exit',
    ])))

Is simply:

    print([label_nums[key] for key in [
            'app.launch', 'app.pause', 'app.resume', 'app.exit', 'app.launch', 'app.pause', 'app.exit', 
            'app.launch', 'app.exit',
        ]])

Benefits:

• no side effects
• clear intents
• native idiomatic syntax
• can be turned into a generator if you want to

Although most Python dev would probably reformat it and provide a default value this way:

events = [
    'app.launch', 
    'app.pause', 
    'app.resume', 
    'app.exit', 
    'app.launch', 
    'app.pause', 
    'app.exit', 
    'app.launch', 
    'app.exit',
]      

print([label_nums.get(event, 'default') for event in events)]

Use Python the way it's intended to be.