In [ 86 ]: sr.disc_list
Out[86]: array([[ 1. , 0.97530991, 0.95122942, 0.92774349, 0.90483742
]])
Cash Flow Series Class with GUI
The last example in this section is about the cash_flow_series class. In principle, we
have seen in the previous example the basic workings of traits when it comes to
presenting results within a GUI window. Here, we only want to add some twists to the
story: for example, a slider to easily change the value for the short rate. In the class
definition that follows, this is accomplished by using the Range function, where we
provide a minimum, a maximum, and a default value. There are also more output fields to
account for the calculation of the present values and the net present value:
In [ 87 ]: class cash_flow_series(trapi.HasTraits):
name = trapi.Str
short_rate = trapi.Range(0.0, 0.5, 0.05)
time_list = trapi.Array(dtype=np.float, shape=( 1 , 6 ))
cash_flows = trapi.Array(dtype=np.float, shape=( 1 , 6 ))
disc_values = trapi.Array(dtype=np.float, shape=( 1 , 6 ))
present_values = trapi.Array(dtype=np.float, shape=( 1 , 6 ))
net_present_value = trapi.Float
update = trapi.Button
def _update_fired(self):
self.disc_values = np.exp(-self.short_rate * self.time_list)
self.present_values = self.disc_values * self.cash_flows
self.net_present_value = np.sum(self.present_values)
v = trui.View(trui.Group(trui.Item(name = ‘name’),
trui.Item(name=‘short_rate’),
trui.Item(name=‘time_list’, label=‘Time List’),
trui.Item(name=‘cash_flows’, label=‘Cash Flows’),
trui.Item(‘update’, show_label=False),
trui.Item(name=‘disc_values’,
label=‘Discount Factors’),
trui.Item(name=‘present_values’,
label=‘Present Values’),
trui.Item(name=‘net_present_value’,
label=‘Net Present Value’),
show_border=True, label=‘Calculate Present Values’),
buttons = [trui.OKButton, trui.CancelButton],
resizable = True)
Apart from the slightly more complex class definition, the usage is still the same:
In [ 88 ]: cfs = cash_flow_series()
In [ 89 ]: cfs.configure_traits()
Figure 13-8 shows the new GUI without any actions taken so far (i.e., empty). Notice the
slider and all the new fields for the cash flow values, the present values, and the net
present value.
Figure 13-9 shows a version of the GUI where input data has been typed in already, but no
other action has taken place.
Finally, Figure 13-10 presents the GUI with both input data and results data — i.e., after
pushing the Update button. Although this is still quite a simple example, the result can
almost be considered an application. We have:
Input
The GUI allows for inputting data to initialize all object attributes.
Logic
There is application logic that calculates discount factors, present values, and an
