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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def connect_float_text(instance, prop, widget, fmt="{:g}"):
 """ Connect a numerical callback property with a Qt widget containing text. Parameters instance : object The class instance that the callback property is attached to prop : str The name of the callback property widget : QtWidget The Qt widget to connect. This should implement the ``setText`` and ``text`` methods as well optionally the ``editingFinished`` signal. fmt : str or func This should be either a format string (in the ``{}`` notation), or a function that takes a number and returns a string. """


    if callable(fmt):
        format_func = fmt
    else:
        def format_func(x):
            return fmt.format(x)

    def update_prop():
        val = widget.text()
        try:
            setattr(instance, prop, float(val))
        except ValueError:
            setattr(instance, prop, 0)

    def update_widget(val):
        if val is None:
            val = 0.
        widget.setText(format_func(val))

    add_callback(instance, prop, update_widget)

    try:
        widget.editingFinished.connect(update_prop)
    except AttributeError:
        pass

    update_widget(getattr(instance, prop))