Logging

cache-results logs with Python’s standard logging, to the cache_results.decorators logger. Configure it in your LOGGING setting like any other.

What is logged

ERROR

A call whose arguments can’t be part of a key, and so runs uncached. It is logged once per process for each function and reason, then at DEBUG, so that a frequently called function can’t flood your logs. See Arguments and Cache Keys.

INFO

Every cache hit, miss and invalidation, when logging is enabled for the function: by its decorator’s logging_enabled=True, or by the LOGGING_ENABLED setting.

DEBUG

The same events when logging isn’t enabled, and calls made before Django is ready.

Messages name the function and the type of its result, never the result itself, so that cached data doesn’t end up in your logs:

INFO cache_results.decorators.@cache_results() caching dict for get_book_summary: myapp.books.get_book_summary()_3f0c..., with timeout 3600
INFO cache_results.decorators.@cache_results() cache hit for get_book_summary: myapp.books.get_book_summary()_3f0c... (dict)

Arguments are added only when VERBOSE_LOGGING is on. Turn it on only where arguments can’t hold personal data.

Turning logging on at runtime

LOGGING_ENABLED and VERBOSE_LOGGING can be callables, called on every cached call. Point them at a feature flag to switch cache logging on in production without a redeploy:

# myapp/cache.py
from waffle import switch_is_active


def cache_logging_enabled() -> bool:
    return switch_is_active("cache_logging")

# settings.py
CACHE_RESULTS = {"LOGGING_ENABLED": "myapp.cache.cache_logging_enabled"}

The callable may query the database: for async functions it is called in a worker thread. Keep it fast, or cache its answer, because it runs on every call.

Formatting the prefix

LOG_PREFIX formats the start of each message, e.g. to color hits and misses in a development console:

def log_prefix(text: str, event: str) -> str:
    colors = {"hit": "\033[32m", "miss": "\033[31m", "invalidate": "\033[37m"}
    color = colors.get(event)
    return f"{color}{text}\033[0m" if color else text