Python switch statement

switch.py

"""
Python switch statement

Usage:
```
from datetime import datetime

# import switch and case (below)


def spring_message(coils=3, is_expanded=False):
    msg = ('\/' if is_expanded else '|/') * coils
    print(msg)
    return msg

def summer_message(current_time):
    msg = "Summertime (at {time}) and the living's easy.".format(time=current_time.strftime('%I:%M%p'))
    print(msg)
    return msg

def fall_message():
    msg = 'Have a nice trip - see you next fall!'
    print(msg)
    return msg

def winter_message(periods=1):
    msg = 'Winter is coming{ellipsis}'.format(ellipsis='.' * periods)
    print(msg)
    return msg

season = 'spring'

switch(
    season,
    dict(
        spring=case(spring_message, coils=7, is_expanded=False),
        summer=case(summer_message, current_time=datetime.utcnow().time()),
        fall=case(fall_message),
        winter=case(winter_message, periods=5, continue_to='spring'),
    ),
    default=42,
)
```
"""

from functools import partial


class Sentinel:
    pass


def switch(value, cases, default=Sentinel):
    try:
        casing = cases[value]
    except KeyError:
        if default is Sentinel:
            raise
        casing = default
    case_value = casing() if callable(casing) else casing
    if hasattr(casing, 'continue_to') and casing.continue_to is not None:
        return switch(casing.continue_to, cases, default=default)
    return case_value


def case(func, continue_to=None, *args, **kwargs):
    partial_func = partial(func, *args, **kwargs)
    partial_func.continue_to = continue_to
    return partial_func