A Python implementation of JavaScript switches

switch.py

"""
swtich.py -- JS switches in Python (proof of concept)
Author: Garin Wally; Nov 2016

Just took the JavaScript tutorial at codecademy and thought switches were
pretty cool, so I coded one up in Python.
I have to admit, this implementation is not great, not pretty, and likely
not shorter than a standard if/elif/else block.
"""

class Switch(object):
    def __init__(self, cases={}):
        self.cases = cases
    def add_case(self, key, value):
        self.cases[key] = value
    def set_default(self, default):
        self.cases['default'] = default
    def __call__(self, case):
        if self.cases == {}:
            raise KeyError("No switch cases exist")
        elif "default" not in self.cases.keys():
            raise KeyError("No default case set")
            
        if case in self.cases.keys():
            if callable(self.cases[case]):
                return self.cases[case]()
            else:
                return self.cases[case]
        else:
            if callable(self.cases['default']):
                return self.cases['default']()
            else:
                return self.cases['default']


# Ideally, you'd import switch and the above code would
#  already be taken care of

switch = Switch()

# Test function
def _test():
    """Namespaced test function."""
    switch = Switch()

    # Setup cases
    def case1():
        return "Switch case 1 activated"

    def case2():
        return "Switch case 2 activated"

    case3 = "Switch case 3 activated"

    # Setup the default case
    def default():
        return "Default case activated"

    # Then add your cases to the switch
    switch.add_case("case1", case1)
    switch.add_case("case2", case2)
    switch.add_case("case3", case3)
    switch.set_default(default)

    # Then use it
    assert switch("case1") == "Switch case 1 activated"
    assert switch("case3") == "Switch case 3 activated"  # non-callable string
    assert switch("not an option") == "Default case activated"
    print("tests passed")