streamlit/streamlit · error · RuntimeError

main_dg is not set

Error message

main_dg is not set

What it means

Error "main_dg is not set" thrown in streamlit/streamlit.

Source

Thrown at lib/streamlit/delta_generator_singletons.py:236

        return self._ensure_context_var().__hash__()


# we don't use the default factory here because `main_dg` is not initialized when this
# module is imported. This is why we have our own ContextVar wrapper.
context_dg_stack: ContextVarWithLazyDefault[tuple[DeltaGenerator, ...]] = (
    ContextVarWithLazyDefault(
        "context_dg_stack", default=lambda: (get_dg_singleton_instance().main_dg,)
    )
)


def get_default_dg_stack_value() -> tuple[DeltaGenerator, ...]:
    """Get the default dg_stack value with which the dg_stack should
    be initialized and reset if needed.
    """
    instance = get_dg_singleton_instance()
    if instance._main_dg is None:
        raise RuntimeError("main_dg is not set")

    return (instance._main_dg,)


def get_last_dg_added_to_context_stack() -> DeltaGenerator | None:
    """Get the last added DeltaGenerator of the stack in the current context.

    Returns None if the stack has only one element or is empty for whatever reason.
    """
    current_stack = context_dg_stack.get()
    # If set to "> 0" and thus return the only delta generator in the stack -
    # which logically makes more sense -, some unit tests fail.
    # It looks like the reason is that they create their own main delta generator
    # but do not populate the dg_stack correctly. However, to be on the safe-side,
    # we keep the logic but leave the comment as shared knowledge for whoever will look
    # into this in the future.
    if len(current_stack) > 1:
        return current_stack[-1]

View on GitHub (pinned to 202661fc55)

When it happens

Trigger: Thrown at lib/streamlit/delta_generator_singletons.py:236 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of streamlit/streamlit@202661fc55 (2026-08-26). Data as JSON: /api/errors/51890abfd56676cb. Report an issue: GitHub.