canni/switch

The missing Python switch statement

Switch

Changelog

• v1.1.0: No BC breaks, new features:

  • Multiple case test within single case (see examples)
  • Cases now support regexp matching (see examples)

• v1.0.4: 15% performance improvement, no BC breaks
• v1.0.3: Maintenance release, no significant code changes
• v1.0.2: 100% unit test coverage

Simple example:

from switch import Switch

def simple_example(val):
    values = []

    with Switch(val) as case:
        if case(1):
            values.append('Found 1')

        if case(2, 3):
            values.append('Found 2 or 3')

    return values

assert simple_example(1) == ['Found 1']
assert simple_example(2) == ['Found 2 or 3']
assert simple_example(3) == ['Found 2 or 3']
assert simple_example('anything else') == []

Simple example with default case:

from switch import Switch

def simple_example_with_default(val):
    values = []

    with Switch(val) as case:
        if case(1):
            values.append('Found 1')

        if case(2, 3):
            values.append('Found 2 or 3')

        if case.default:
            values.append('No love for 1, 2 or 3?')

    return values

assert simple_example_with_default(1) == ['Found 1']
assert simple_example_with_default(2) == ['Found 2 or 3']
assert simple_example_with_default(3) == ['Found 2 or 3']
assert simple_example_with_default('anything else') == ['No love for 1, 2 or 3?']

Fall through example:

from switch import Switch

def fall_through_example(val):
    values = []

    with Switch(val) as case:
        if case(1, fall_through=True):
            values.append('Found 1')

        if case(2, 3):
            values.append('Found 2 or 3')

        if case.default:
            values.append('No love for 1, 2 or 3?')

    return values

assert fall_through_example(1) == ['Found 1', 'Found 2 or 3']
assert fall_through_example(2) == ['Found 2 or 3']
assert fall_through_example(3) == ['Found 2 or 3']
assert fall_through_example('anything else') == ['No love for 1, 2 or 3?']

Cases can have callable test:

from switch import Switch

def ouh_callable_too(val):
    values = []

    with Switch(val) as case:
        if case(1):
            values.append('Found 1')

        if case.call(lambda v: v < 100):
            values.append('Found <100')

        if case.default:
            values.append('No love for anything lower than 100?')

    return values

assert ouh_callable_too(1) == ['Found 1']
assert ouh_callable_too(50) == ['Found <100']
assert ouh_callable_too('anything else') == ['No love for anything lower than 100?']

Cases can have test against regexp:

from switch import Switch

def test_regexp(val):
    values = []

    with Switch(val) as case:
        if case(1):
            values.append('Found 1')

        if case.match(r'10|ten'):
            values.append('Found 10')

        if case.default:
            values.append('No love for 1 or 10?')

    return values

assert test_regexp(1) == ['Found 1']
assert test_regexp(10) == ['Found 10']
assert test_regexp('ten') == ['Found 10']
assert test_regexp('anything else') == ['No love for 1 or 10??']

Fall through by default:

from switch import CSwitch, Switch

def fall_through_by_default(val):
    values = []

    with Switch(val, fall_through=True) as case:
        if case(1):
            values.append('Found 1')

        if case(2):
            values.append('Found 2')

        if case(3, fall_through=False):
            values.append('Found 3')

        if case(4):
            values.append('Found 4')

        if case.default:
            values.append('No love for 1, 2, 3 or 4?')

    return values


def cswitch_shortcut(val):
    values = []

    with CSwitch(val) as case:
        if case(1):
            values.append('Found 1')

        if case(2):
            values.append('Found 2')

        if case(3, fall_through=False):
            values.append('Found 3')

        if case(4):
            values.append('Found 4')

        if case.default:
            values.append('No love for 1, 2, 3 or 4?')

    return values

assert fall_through_by_default(1) == ['Found 1', 'Found 2', 'Found 3']
assert fall_through_by_default(2) == ['Found 2', 'Found 3']
assert fall_through_by_default(3) == ['Found 3']
assert fall_through_by_default(4) == ['Found 4']
assert fall_through_by_default('anything else') == ['No love for 1, 2, 3 or 4?']

assert cswitch_shortcut(1) == fall_through_by_default(1)
assert cswitch_shortcut(2) == fall_through_by_default(2)
assert cswitch_shortcut(3) == fall_through_by_default(3)
assert cswitch_shortcut(4) == fall_through_by_default(4)
assert cswitch_shortcut('anything else') == fall_through_by_default('anything else')

Having a case after a default is a bad thing:

• Unless some case executes early and finishes without fall through.

from switch import Switch

def case_after_default_is_baad(val):
    values = []

    with Switch(val) as case:
        if case(1):
            values.append('Found 1')

        if case.default:
            values.append('Found default')

        if case('this is baad'):
            values.append('Should not happen!')

    return values

assert case_after_default_is_baad(1) == ['Found 1']

try:
    case_after_default_is_baad('this is baad')
    assert False
except SyntaxError:
    assert True