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[Feature Request] Partial Pattern Matching #3764
Description
Summary
I use Dash pattern-matching callbacks extensively in my multi-page apps and make heavy use of the ALL wildcard. However, the callback architecture of my apps could be simplified further by introducing an option to allow partial matches, where a pattern with fewer keys matches components that have a superset of those keys.
This proposes an opt-in partial=True flag on Input, Output, and State.
Motivation
Currently, pattern-matching callbacks require the pattern and component to share exactly the same set of keys:
# Pattern: {"type": "btn", "index": ALL}
# Only matches: {"type": "btn", "index": 1}, {"type": "btn", "index": 2}
# Does NOT match: {"type": "btn", "index": 1, "page": "home"}This forces developers to either:
- Ensure all related components have identical key sets (rigid, often impractical)
- Create separate callbacks for each key combination (verbose, duplicated logic)
- Use
callback_contextworkarounds to multiplex unrelated callbacks
I find with my apps I frequently have components that share a conceptual "type" but differ in their additional metadata keys — pages, sections, tabs, permissions, etc.
Proposed API
from dash import Input, Output, State, ALL, MATCH
# Literal partial: matches all components with type="btn", regardless of extra keys
@app.callback(
Output("output", "children"),
Input({"type": "btn"}, "n_clicks", partial=True),
)
def handle_all_btns(n_clicks_list):
# Receives a list (implicitly multi-valued since multiple components match)
return f"Total: {sum(c or 0 for c in n_clicks_list)}"
# With ALL wildcard: collects all components that have a "type" key
@app.callback(
Output("output", "children"),
Input({"type": ALL}, "n_clicks", partial=True),
)
def handle_any_type(n_clicks_list):
return f"Collected {len(n_clicks_list)} components"
# With MATCH: one-at-a-time on the shared key, ignoring extra keys
@app.callback(
Output({"type": "display", "index": MATCH}, "children", partial=True),
Input({"type": "btn", "index": MATCH}, "n_clicks", partial=True),
)
def handle_one(n_clicks):
return f"Clicked {n_clicks} times"
Activity