from tkinter import TclError
class WidgetRedirector:
"""Support for redirecting arbitrary widget subcommands.
Some Tk operations don't normally pass through tkinter. For example, if a
character is inserted into a Text widget by pressing a key, a default Tk
binding to the widget's 'insert' operation is activated, and the Tk library
processes the insert without calling back into tkinter.
Although a binding to <Key> could be made via tkinter, what we really want
to do is to hook the Tk 'insert' operation itself. For one thing, we want
a text.insert call in idle code to have the same effect as a key press.
When a widget is instantiated, a Tcl command is created whose name is the
same as the pathname widget._w. This command is used to invoke the various
widget operations, e.g. insert (for a Text widget). We are going to hook
this command and provide a facility ('register') to intercept the widget
operation. We will also intercept method calls on the tkinter class
instance that represents the tk widget.
In IDLE, WidgetRedirector is used in Percolator to intercept Text
commands. The function being registered provides access to the top
of a Percolator chain. At the bottom of the chain is a call to the
original Tk widget operation.
"""
def __init__(self, widget):
'''Initialize attributes and setup redirection.
_operations: dict mapping operation name to new function.
widget: the widget whose tcl command is to be intercepted.
tk: widget.tk, a convenience attribute, probably not needed.
orig: new name of the original tcl command.
Since renaming to orig fails with TclError when orig already
exists, only one WidgetDirector can exist for a given widget.
'''
self._operations = {}
self.widget = widget # widget instance
self.tk = tk = widget.tk # widget's root
w = widget._w # widget's (full) Tk pathname
self.orig = w + "_orig"
# Rename the Tcl command within Tcl:
tk.call("rename", w, self.orig)
# Create a new Tcl command whose name is the widget's pathname, and
# whose action is to dispatch on the operation passed to the widget:
tk.createcommand(w, self.dispatch)
def __repr__(self):
w = self.widget
return f"{self.__class__.__name__,}({w.__class__.__name__}<{w._w}>)"
def close(self):
"Unregister operations and revert redirection created by .__init__."
for operation in list(self._operations):
self.unregister(operation)
widget = self.widget
tk = widget.tk
w = widget._w
# Restore the original widget Tcl command.
tk.deletecommand(w)
tk.call("rename", self.orig, w)
del self.widget, self.tk # Should not be needed
# if instance is deleted after close, as in Percolator.
def register(self, operation, function):
'''Return OriginalCommand(operation) after registering function.
Registration adds an operation: function pair to ._operations.
It also adds a widget function attribute that masks the tkinter
class instance method. Method masking operates independently
from command dispatch.
If a second function is registered for the same operation, the
first function is replaced in both places.
'''
self._operations[operation] = function
setattr(self.widget, operation, function)
return OriginalCommand(self, operation)
def unregister(self, operation):
'''Return the function for the operation, or None.
Deleting the instance attribute unmasks the class attribute.
'''
if operation in self._operations:
function = self._operations[operation]
del self._operations[operation]
try:
delattr(self.widget, operation)
except AttributeError:
pass
return function
else:
return None
def dispatch(self, operation, *args):
'''Callback from Tcl which runs when the widget is referenced.
If an operation has been registered in self._operations, apply the
associated function to the args passed into Tcl. Otherwise, pass the
operation through to Tk via the original Tcl function.
Note that if a registered function is called, the operation is not
passed through to Tk. Apply the function returned by self.register()
to *args to accomplish that. For an example, see colorizer.py.
'''
operation = str(operation) # can be a Tcl_Obj
m = self._operations.get(operation)
try:
if m:
return m(*args)
else:
return self.tk.call((self.orig, operation) + args)
except TclError:
return ""
class OriginalCommand:
'''Callable for original tk command that has been redirected.
Returned by .register; can be used in the function registered.
redir = WidgetRedirector(text)
def my_insert(*args):
print("insert", args)
original_insert(*args)
original_insert = redir.register("insert", my_insert)
'''
def __init__(self, redir, operation):
'''Create .tk_call and .orig_and_operation for .__call__ method.
.redir and .operation store the input args for __repr__.
.tk and .orig copy attributes of .redir (probably not needed).
'''
self.redir = redir
self.operation = operation
self.tk = redir.tk # redundant with self.redir
self.orig = redir.orig # redundant with self.redir
# These two could be deleted after checking recipient code.
self.tk_call = redir.tk.call
self.orig_and_operation = (redir.orig, operation)
def __repr__(self):
return f"{self.__class__.__name__,}({self.redir!r}, {self.operation!r})"
def __call__(self, *args):
return self.tk_call(self.orig_and_operation + args)
def _widget_redirector(parent): # htest #
from tkinter import Toplevel, Text
top = Toplevel(parent)
top.title("Test WidgetRedirector")
x, y = map(int, parent.geometry().split('+')[1:])
top.geometry("+%d+%d" % (x, y + 175))
text = Text(top)
text.pack()
text.focus_set()
redir = WidgetRedirector(text)
def my_insert(*args):
print("insert", args)
original_insert(*args)
original_insert = redir.register("insert", my_insert)
if __name__ == "__main__":
from unittest import main
main('idlelib.idle_test.test_redirector', verbosity=2, exit=False)
from idlelib.idle_test.htest import run
run(_widget_redirector)
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