Class VarTrace

Lib/idlelib/configdialog.py:2217–2275

Maintain Tk variables trace state.

class VarTrace:
    """Maintain Tk variables trace state."""

    def __init__(self):
        """Store Tk variables and callbacks.

        untraced: List of tuples (var, callback)
            that do not have the callback attached
            to the Tk var.
        traced: List of tuples (var, callback) where
            that callback has been attached to the var.
        """
        self.untraced = []
        self.traced = []

    def clear(self):
        "Clear lists (for tests)."
        # Call after all tests in a module to avoid memory leaks.
        self.untraced.clear()
        self.traced.clear()

    def add(self, var, callback):
        """Add (var, callback) tuple to untraced list.

        Args:
            var: Tk variable instance.
            callback: Either function name to be used as a callback
                or a tuple with IdleConf config-type, section, and
                option names used in the default callback.

        Return:
            Tk variable instance.
        """
        if isinstance(callback, tuple):
            callback = self.make_callback(var, callback)
        self.untraced.append((var, callback))
        return var

    @staticmethod
    def make_callback(var, config):
        "Return default callback function to add values to changes instance."
        def default_callback(*params):
            "Add config values to changes instance."
            changes.add_option(*config, var.get())
        return default_callback

    def attach(self):
        "Attach callback to all vars that are not traced."
        while self.untraced:
            var, callback = self.untraced.pop()
            var.trace_add('write', callback)
            self.traced.append((var, callback))

    def detach(self):
        "Remove callback from traced vars."
        while self.traced:
            var, callback = self.traced.pop()
            var.trace_remove('write', var.trace_info()[0][1])