86 lines
3.0 KiB
Python
86 lines
3.0 KiB
Python
# Copyright (c) Streamlit Inc. (2018-2022) Snowflake Inc. (2022-2025)
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from __future__ import annotations
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from typing import TYPE_CHECKING, Any, Final
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from streamlit.logger import get_logger
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_LOGGER: Final = get_logger(__name__)
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if TYPE_CHECKING:
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from streamlit.runtime.state.session_state import SessionState
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def apply_presenter(
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session_state: SessionState, widget_id: str, base_value: Any
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) -> Any:
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"""Return the user-visible value for a widget if it has a ``presenter``.
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If the widget's metadata defines a ``presenter`` callable, it is used to
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transform the stored value into its presentation form. Any exception raised
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while resolving metadata or invoking the presenter is swallowed and
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``base_value`` is returned, so presentation never interferes with core
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behavior.
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Notes
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-----
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Presentation is applied exclusively for user-facing access paths such as:
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- `st.session_state[... ]` via `SessionState.__getitem__`
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- `SessionState.filtered_state`
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Internal serialization paths (for example `WStates.as_widget_states()` and
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`SessionState.get_widget_states()`) must operate on base (unpresented)
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values to ensure stable and lossless serialization. Do not use
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`apply_presenter` in serialization code paths.
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Parameters
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----------
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session_state : SessionState
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The current session state object that holds widget state and metadata.
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widget_id : str
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The identifier of the widget whose value is being presented.
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base_value : Any
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The raw value stored for the widget.
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Returns
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-------
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Any
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The value that should be shown to the user.
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"""
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try:
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meta = session_state._get_widget_metadata(widget_id)
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presenter = getattr(meta, "presenter", None) if meta is not None else None
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if presenter is None:
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return base_value
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# Ensure the presenter is callable to avoid silently failing on a
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# TypeError when attempting to invoke a non-callable value.
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if not callable(presenter):
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_LOGGER.warning(
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"Widget '%s' has a non-callable presenter (%r); returning base value.",
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widget_id,
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presenter,
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)
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return base_value
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try:
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return presenter(base_value, session_state)
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except Exception:
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return base_value
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except Exception:
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# If metadata is unavailable or any other error occurs, degrade gracefully.
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return base_value
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