Opt-in 'Clear all' button on a function's form

streamlitfront/elements/elements.py

@@ -111,6 +111,18 @@ def render_views(self):
         view_runner()  # runs the page with the state
 
 
+def _clear_inputs(input_keys):
+    """Forget the state of every widget under ``input_keys`` (the input itself, its view,
+    "None" toggle, ``*args`` count and fields), so each falls back to its default.
+
+    Meant as a button ``on_click``: Streamlit lets callbacks drop widget keys before the rerun.
+    """
+    prefixes = tuple(f"{k}_" for k in input_keys)
+    for key in list(st.session_state.keys()):
+        if key in input_keys or key.startswith(prefixes):
+            del st.session_state[key]
+
+
 class View(FrontContainerBase):
     def render(self):
         st.markdown(f"""## **{self.name}**""", help=self.tooltip)
@@ -152,6 +164,7 @@ def __init__(
         on_submit: Callable[[Any], None] = None,
         use_expander: bool = True,
         submit_button_label: str = "Submit",
+        clear_button_label: str = None,
         authentification: bool = False,
         tooltip: str = None,
     ):
@@ -167,6 +180,7 @@ def __init__(
         )
         self.use_expander = use_expander
         self.submit_button_label = submit_button_label
+        self.clear_button_label = clear_button_label
         self.authentification = authentification
         if authentification:
             if on_submit is None:
@@ -192,12 +206,27 @@ def _render_section_content(self):
         for uploader in _file_uploaders(self.children):
             uploader._slot = None
         inputs = self._render_inputs()
+        if self.clear_button_label:
+            st.button(
+                self.clear_button_label,
+                key=f"{self.name}_clear_all",
+                on_click=_clear_inputs,
+                args=(self._input_keys(),),
+                help="Reset every field to its default",
+            )
         if self.auto_submit or st.button(self.submit_button_label):
             try:
                 self._submit(inputs)
             except ValidationError as e:
                 st.error(e)
 
+    def _input_keys(self) -> list:
+        return [
+            child.input_key
+            for child in self.children
+            if isinstance(child, InputBase) and child.input_key
+        ]
+
     def _render_inputs(self):
         """Render the inputs; a ``*args`` parameter gets a "+" button and one field per press."""
         inputs = {}

tests/test_clear_all.py

@@ -0,0 +1,38 @@
+"""An opt-in "Clear all" button resets a view's fields to their defaults
+(i2mint/streamlitfront#29). Runs the app headlessly with ``AppTest``."""
+
+import pytest
+
+pytest.importorskip("streamlit.testing.v1")
+from streamlit.testing.v1 import AppTest
+
+APP = """
+from front import RENDERING_KEY
+from streamlitfront import mk_app
+def greet(who: str = "world", times: int = 1):
+    return (who + " ") * times
+mk_app([greet], config={RENDERING_KEY: {"greet": {"execution": {"clear_button_label": "Clear all"}}}})()
+"""
+
+NO_CLEAR = APP.replace('"clear_button_label": "Clear all"', '"auto_submit": False')
+
+
+def _button(at, label):
+    return next((b for b in at.button if b.label == label), None)
+
+
+def test_clear_all_restores_defaults():
+    at = AppTest.from_string(APP, default_timeout=30).run()
+    assert not at.exception
+    at.text_input[0].set_value("moon").run()
+    at.number_input[0].set_value(4).run()
+    assert at.text_input[0].value == "moon"
+    _button(at, "Clear all").click().run()
+    assert not at.exception
+    assert at.text_input[0].value == "world"
+    assert at.number_input[0].value == 1
+
+
+def test_no_clear_button_by_default():
+    at = AppTest.from_string(NO_CLEAR, default_timeout=30).run()
+    assert _button(at, "Clear all") is None