mock_now() — langchain Function Reference

Architecture documentation for the mock_now() function in utils.py from the langchain codebase.

Function python Observability TelemetryUtilities calls 1

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Observability→ TelemetryUtilities→ mock_now() — langchain Function Reference

Dependency Diagram

graph TD
  134db6ff_44dc_a037_5d16_5637e58f9750["mock_now()"]
  b77fd012_b825_e350_c8f5_a8f1b44997d9["utils.py"]
  134db6ff_44dc_a037_5d16_5637e58f9750 -->|defined in| b77fd012_b825_e350_c8f5_a8f1b44997d9
  a7fdd325_2e44_73a8_fe05_2212f3ba1948["now()"]
  134db6ff_44dc_a037_5d16_5637e58f9750 -->|calls| a7fdd325_2e44_73a8_fe05_2212f3ba1948
  style 134db6ff_44dc_a037_5d16_5637e58f9750 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/utils/utils.py lines 74–113

def mock_now(dt_value: datetime.datetime) -> Iterator[type]:
    """Context manager for mocking out datetime.now() in unit tests.

    Args:
        dt_value: The datetime value to use for datetime.now().

    Yields:
        The mocked datetime class.

    Example:
        ```python
        with mock_now(datetime.datetime(2011, 2, 3, 10, 11)):
            assert datetime.datetime.now() == datetime.datetime(2011, 2, 3, 10, 11)
        ```
    """

    class MockDateTime(datetime.datetime):
        """Mock datetime.datetime.now() with a fixed datetime."""

        @classmethod
        @override
        def now(cls, tz: datetime.tzinfo | None = None) -> "MockDateTime":
            # Create a copy of dt_value.
            return MockDateTime(
                dt_value.year,
                dt_value.month,
                dt_value.day,
                dt_value.hour,
                dt_value.minute,
                dt_value.second,
                dt_value.microsecond,
                dt_value.tzinfo,
            )

    real_datetime = datetime.datetime
    datetime.datetime = MockDateTime  # type: ignore[misc]
    try:
        yield datetime.datetime
    finally:
        datetime.datetime = real_datetime  # type: ignore[misc]