/* PR_START p--misc 04 */ Allow lazy evaluation of arguments in LazyFormat.

Author: plypaul

metricflow-semantics/metricflow_semantics/mf_logging/lazy_formattable.py

@@ -1,12 +1,15 @@
 from __future__ import annotations
 
+import logging
 from functools import cached_property
 from typing import Callable, Union
 
 from typing_extensions import override
 
 from metricflow_semantics.mf_logging.pretty_print import mf_pformat_dict
 
+logger = logging.getLogger(__name__)
+
 
 class LazyFormat:
     """Lazily formats the given objects into a string representation for logging.
@@ -40,7 +43,8 @@ def __init__(self, message: Union[str, Callable[[], str]], **kwargs) -> None:  #
 
         Args:
             message: The message or a function that returns a message.
-            **kwargs: A dictionary of objects to format to text when `__str__` is called on this object.
+            **kwargs: A dictionary of objects to format to text when `__str__` is called on this object. To allow for
+            lazy evaluation of argument values, a callable that takes no arguments can be supplied for a key's value.
         """
         self._message = message
         self._kwargs = kwargs
@@ -52,7 +56,23 @@ def _str_value(self) -> str:
             message = self._message()
         else:
             message = self._message
-        return mf_pformat_dict(message, self._kwargs, preserve_raw_strings=True)
+
+        evaluated_args = {}
+        for arg_name, arg_value in self._kwargs.items():
+            if callable(arg_value):
+                try:
+                    evaluated_args[arg_name] = arg_value()
+                    continue
+                except Exception:
+                    logger.warning(
+                        f"Got an exception while evaluating {arg_name=} {arg_value=}. Since this is an error with "
+                        f"formatting log output, this should not result in system issues. However, the exception "
+                        f"indicates a bug with how the logging call is made and should be investigated.",
+                        exc_info=True,
+                    )
+
+            evaluated_args[arg_name] = arg_value
+        return mf_pformat_dict(message, evaluated_args, preserve_raw_strings=True)
 
     @override
     def __str__(self) -> str:

metricflow-semantics/tests_metricflow_semantics/mf_logging/test_lazy_format.py

@@ -9,6 +9,8 @@
 
 logger = logging.getLogger(__name__)
 
+_NOT_FORMATTED_ASSERTION_MESSAGE = "This should not have been formatted as a string."
+
 
 def test_log_kwargs() -> None:
     """Test that objects included via keyword args are formatted."""
@@ -36,12 +38,11 @@ def test_lambda() -> None:
 
 def test_lazy_object() -> None:
     """Test that formatting of objects are done lazily and not when the logging level is not appropriate."""
-    assertion_message = "This should not have been formatted as a string."
 
     class _NotFormattedObject:
         @override
         def __repr__(self) -> str:
-            raise AssertionError(assertion_message)
+            raise AssertionError(_NOT_FORMATTED_ASSERTION_MESSAGE)
 
     # Logging level is INFO, so DEBUG messages shouldn't be logged / formatted.
     recorded_logger: logging.Logger
@@ -51,14 +52,35 @@ def __repr__(self) -> str:
 
 
 def test_lazy_lambda() -> None:
-    """Test that a lambda input is not evaluated when the logging level is not appropriate."""
-    assertion_message = "This should not have been formatted as a string."
+    """Test that a lambda message is not evaluated when the logging level is not appropriate."""
 
     def _should_not_be_called() -> str:
-        raise AssertionError(assertion_message)
+        raise AssertionError(_NOT_FORMATTED_ASSERTION_MESSAGE)
 
     # Logging level is INFO, so DEBUG messages shouldn't be logged / formatted.
     recorded_logger: logging.Logger
     handler: RecordingLogHandler
     with recorded_logging_context(logger, logging.INFO) as (recorded_logger, handler):
         recorded_logger.debug(LazyFormat(lambda: f"{_should_not_be_called()}"))
+
+
+def test_lambda_argument() -> None:
+    """Tests that a callable that's supplied as an argument value is evaluated."""
+    recorded_logger: logging.Logger
+    handler: RecordingLogHandler
+    with recorded_logging_context(logger, logging.INFO) as (recorded_logger, handler):
+        recorded_logger.info(LazyFormat("Example message", arg_0=lambda: 1))
+        assert handler.get_last_message() == "Example message (arg_0=1)"
+
+
+def test_lazy_lambda_argument() -> None:
+    """Test that a lambda input is not evaluated when the logging level is not appropriate."""
+
+    def _should_not_be_called() -> str:
+        raise AssertionError(_NOT_FORMATTED_ASSERTION_MESSAGE)
+
+    # Logging level is INFO, so DEBUG messages shouldn't be logged / formatted.
+    recorded_logger: logging.Logger
+    handler: RecordingLogHandler
+    with recorded_logging_context(logger, logging.INFO) as (recorded_logger, handler):
+        recorded_logger.debug(LazyFormat("Example message", arg_0=lambda: f"{_should_not_be_called()}"))