Lazy Evaluation

Use opt(lazy=True) to defer message evaluation until the log is actually emitted.

Lazy Message Arguments

from logly import logger

def get_user_data():
    print("Expensive query executed")
    return {"name": "alice", "role": "admin"}

logger.opt(lazy=True).debug("User data: {}", get_user_data)
# "Expensive query executed" only prints if DEBUG is enabled
logger.complete()

Lazy with Lambda

from logly import logger

items = list(range(1000))
logger.opt(lazy=True).debug("Processing {} items", lambda: len(items))
logger.complete()

Exception Capture

from logly import logger

try:
    risky_operation()
except Exception:
    logger.opt(exception=True).error("Operation failed")
logger.complete()

Performance benefit

Lazy evaluation avoids the cost of string formatting or function calls when the log level is filtered out.

Combine with exception=True

logger.opt(exception=True) captures the current exception and appends the traceback automatically.