Logger

easy · levels, filtering, sink injection

Brief-reported interview attribution (unverified): Amazon, Microsoft

Design a logging framework. Levels are DEBUG < INFO < WARN < ERROR. The logger is created with a level; messages below that level are dropped. log(level, message) formats a message as "[LEVEL] message". Output goes to a sink callable passed to the constructor, or to an internal list (read via messages()) when no sink is given. Invalid levels raise ValueError.

class Logger:
    def __init__(self, level="INFO", sink=None):
        # sink: callable taking one formatted string, or None
    def set_level(self, level):
        # raises ValueError for an unknown level
    def log(self, level, message):
        # raises ValueError for an unknown level; drops messages below the set level
    def debug(self, message):
    def info(self, message):
    def warn(self, message):
    def error(self, message):
    def messages(self):
        # -> list of formatted strings (empty when a sink is used)

Rules. The default level is "INFO". set_level and log with an unknown level raise ValueError. A dropped message is never sent to the sink and never stored.

Tests use explicit inputs and injected clocks/callbacks. No network, real threads or application-server execution is involved.

Public demo

# Public demo: run after implementing the class API above.
l = Logger()
l.debug('dropped')
l.info('started')
l.warn('slow')
l.error('failed')
print(l.messages())

Starter code

class Logger:

    def __init__(self, level='INFO', sink=None):
        """sink: callable taking one formatted string, or None"""
        pass

    def set_level(self, level):
        """raises ValueError for an unknown level"""
        pass

    def log(self, level, message):
        """raises ValueError for an unknown level; drops messages below the set level"""
        pass

    def debug(self, message):
        """Implement the return value and rules in the API contract."""
        pass

    def info(self, message):
        """Implement the return value and rules in the API contract."""
        pass

    def warn(self, message):
        """Implement the return value and rules in the API contract."""
        pass

    def error(self, message):
        """Implement the return value and rules in the API contract."""
        pass

    def messages(self):
        """-> list of formatted strings (empty when a sink is used)"""
        pass

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