Add 'on_demand' option to interact() so that long-running functions can be started only when explicitly requested

IPython/html/widgets/interaction.py

@@ -23,7 +23,7 b' from inspect import getcallargs'
 from IPython.core.getipython import get_ipython
 from IPython.html.widgets import (Widget, TextWidget,
     FloatSliderWidget, IntSliderWidget, CheckboxWidget, DropdownWidget,
-    ContainerWidget, DOMWidget)
+    ContainerWidget, DOMWidget, ButtonWidget)
 from IPython.display import display, clear_output
 from IPython.utils.py3compat import string_types, unicode_type
 from IPython.utils.traitlets import HasTraits, Any, Unicode
@@ -175,6 +175,7 b' def interactive(__interact_f, **kwargs):'
     """Build a group of widgets to interact with a function."""
     f = __interact_f
     co = kwargs.pop('clear_output', True)
+    on_demand = kwargs.pop('on_demand', False)
     kwargs_widgets = []
     container = ContainerWidget()
     container.result = None
@@ -194,10 +195,15 b' def interactive(__interact_f, **kwargs):'
     # so that traitlets notices the update. We skip any objects (such as fixed) that
     # are not DOMWidgets.
     c = [w for w in kwargs_widgets if isinstance(w, DOMWidget)]
+
+    # If we are only to run the function on demand, add a button to request this
+    if on_demand:
+        on_demand_button = ButtonWidget(description="Run %s" % f.__name__)
+        c.append(on_demand_button)
     container.children = c
 
     # Build the callback
-    def call_f(name, old, new):
+    def call_f(name=None, old=None, new=None):
         container.kwargs = {}
         for widget in kwargs_widgets:
             value = widget.value
@@ -214,6 +220,12 b' def interactive(__interact_f, **kwargs):'
                 ip.showtraceback()
 
     # Wire up the widgets
+    # If we are doing on demand running, the callback is only triggered by the button
+    # Otherwise, it is triggered for every trait change received
+    # On-demand running also suppresses running the fucntion with the initial parameters
+    if on_demand:
+        on_demand_button.on_click(call_f)
+    else:
     for widget in kwargs_widgets:
         widget.on_trait_change(call_f, 'value')