# Tutorial: Adding an Interactive Tool

This section provides a guided tutorial on adding an interactive utility to PyARPES. Internally, support is provided to make it straightforward to add an interactivity using

1. bokeh: an option for interactivity inside Jupyter

2. matplotlib + Qt: interactive popout Matplotlib figures

3. Native Qt Applications: Fast native applications for heavier applications

This section will cover the third option and show how Qt5 and pyqtgraph can be used to make an interactive tool that allows you to tune function parameters applied to a spectrum. Examples of the other options can be found in the source for bokeh_tool/.S.show (bokeh) and widgets.py (matplotlib).

## Structure

We will put our utility into two files, one which will contain the code for the tool, another with a manual test harness so we can start it quickly. Relative to the source root, these files can be

1. arpes/plotting/dynamic_tool.py

2. scripts/test_dynamic_tool.py

## Test Harness

Let’s first write the test script. This is straightforward since we can use the example data with our function using arpes.io.load_example_data.

In order to provide a parameterized function that we can test on the data we we can also define the function adjust_gamma which rescales the intensity in a spectrum according to $$x \rightarrow x^\gamma$$.

Finally, we can invoke our not-yet existent function make_dynamic which we can decide will take the function as the first argument and the data as the second argument.

from arpes.io import load_example_data
from arpes.plotting.dynamic_tool import make_dynamic

def adjust_gamma(data, gamma: float = 1):
"""
Equivalent to adjusting the display gamma factor, just rescale the data
according to f(x) = x^gamma.

:param data:
:param gamma:
:return:
"""
return data ** gamma



To test our code, we can now run this script which will handle the imports and data loading for us. Currently, it fails because we have not yet defined the module arpes.plotting.dynamic_tool

## Writing the Interactive Utility

Now that we have a script we can use to call our utility while we write it, we can focus on scripting the UI and dealing with the business logic.

### Application Structure and Lifecycle

Qt-based applications in PyARPES are managed according to their lifecycle. A summary of the lifecycle of an interactive utility in PyARPES is included here for reference.

For the most part, you should not need to modify the parts in blue boxes, although you can do so if needed. Generally, you will need to fill out the layout function as well as before_show where you may perform additional layout logic or initialization as required by your application.

Although not typically required a hook after_show is also available in case any Qt or pyqtgraph settings need adjusting after the initial draw to the screen.

Once running, interaction is provided through mouse and keyboard handlers, until a request is made to close it. This can occur due to an unhandled Exception, the user pressing Esc, the user clicking the window close button, or programmatically.

### Getting a Window

There’s a bit of starter code we need before we get too deep. As a first step we will add only as much as is needed to spawn a window.

from PyQt5 import QtWidgets
from arpes.utilities.qt import qt_info, SimpleApp, SimpleWindow, BasicHelpDialog

__all__ = ('DynamicTool', 'make_dynamic',)

qt_info.setup_pyqtgraph()

class DynamicToolWindow(SimpleWindow):
HELP_DIALOG_CLS = BasicHelpDialog

class DynamicTool(SimpleApp):
WINDOW_SIZE = (5,5,) # 5 inches by 5 inches
WINDOW_CLS = DynamicToolWindow
TITLE = '' # we will use the function name for the window title

def __init__(self, function):
self._function = function
self.main_layout = QtWidgets.QGridLayout()
self.data = None

super().__init__()

def set_data(self, data):
pass

def layout(self):
return self.main_layout

def make_dynamic(fn, data):
tool = DynamicTool(fn)
tool.set_data(data)
tool.start()


As we can see, we added two classes DynamicToolWindow, which handles responding to events like keyboard shortcuts, and DynamicTool, which handles the logic of our application and is responsible for actually drawing and delegating the UI.

We will add more code to each later. For now, notice that we declare a help page class via HELP_DIALOG_CLS = BasicHelpDialog: this will provide a help panel summarizing the available keyboard shortcuts. You can open this panel by pressing ‘H’ on any running interactive application in PyARPES.

In DynamicTool, we set the window size desired in inches on the screen, as well as the window class which we set to DynamicToolWindow. We can leave the window title blank because later we will set it to the name of the function we call the panel with.

### Displaying Data

A next step is to display the original data.

class DynamicTool(SimpleApp):
...

def configure_image_widgets(self):
self.generate_marginal_for((), 0, 0, 'xy', cursors=False, layout=self.content_layout)
self.generate_marginal_for((), 1, 0, 'f(xy)', cursors=False, layout=self.content_layout)

def update_data(self):
self.views['xy'].setImage(self.data.S.nan_to_num())
self.views['f(xy)'].setImage(self.data.S.nan_to_num()) # for now just display the same data

pass

def before_show(self):
self.configure_image_widgets()
self.update_data()

def set_data(self, data: DataType):
self.data = normalize_to_spectrum(data)


To display the data, we added logic in the before_show lifecycle hook to generate plots for the data (xy) and the transformed data (f(xy)). To do this we used the utility function generate_marginal_for that can be used to create browsable marginal plots for high dimensional data sets. Here we do not want to integrate out any dimensions so we passed an tuple as the first argument. With the rest of the invokation we specify to add the plot to the layout self.content_layout in the locations (0,0) and (1,0). Because we are not linking plots we don’t need cursors.

We can also add a function update_data in order to set the data on each of these views.

### Generating controls from the function

In order to generate controls, we need to know the types and default values of arguments. Using inspect.getfullargspec we can introspect the arguments to the supplied function. We will make the reasonable assumption that the user is supplying type annotations but that default values may not be available.

class DynamicTool(SimpleApp):
...
def __init__(self, function):
...
self.current_arguments = {}

super().__init__()

def calculate_control_specification(self):
argspec = inspect.getfullargspec(self._function)

# we assume that the first argument is the input data
args = argspec.args[1:]

defaults_for_type = {
float: 0.,
int: 0,
str: '',
}

specs = []
for i, arg in enumerate(args[::-1]):
argument_type = argspec.annotations.get(arg, float)
if i < len(argspec.defaults):
argument_default = argspec.defaults[len(argspec.defaults) - (i+1)]
else:
argument_default = defaults_for_type.get(argument_type, 0)

self.current_arguments[arg] = argument_default
specs.append([
arg,
argument_type,
argument_default,
])

return specs


Now that we can generate from a type annotated function a description of the parameters, we can use this to generate UI inputs (controls) for these parameters and render them into our utility.

For each control, we will “subscribe” to changes in the value so that we can update the plot with the new value of the function called with the updated parameters. To do this, we will add two new functions add_controls and build_control_for. build_control_for is simple, it just takes the description of the parameter we computed with calculate_control_specification and returns an appropriate widget. Notice that we pass an ID with the parameter name when we construct the UI element. This allows us to find the control later and subscribe to changes.

In add_controls we:

1. Calculate the parameter description

2. Inside CollectUI(ui) iterate across these parameter descriptions and group them into a “Controls” tab of the UI.

3. Iterate across the controls and attach a function which responds to changes in the UI update_argument

4. Add the tabbed region to the main UI (self.main_layout.addWidget(controls, 1, 0))

Finally, in update_data we modify the code to invoke the function with the new parameters and update the view.

class DynamicTool(SimpleApp):
...
def update_data(self):
self.views['xy'].setImage(self.data.S.nan_to_num())
try:
mapped_data = self._function(self.data, **self.current_arguments)
self.views['f(xy)'].setImage(mapped_data.S.nan_to_num())
except:
pass

specification = self.calculate_control_specification()

ui = {}
with CollectUI(ui):
controls = tabs(
['Controls', horizontal(
*[vertical(*[vertical(label(s[0]), self.build_control_for(*s)) for s in pair])
for pair in group_by(2, specification)])],
)

def update_argument(arg_name, arg_type):
def updater(value):
self.current_arguments[arg_name] = arg_type(value)
self.update_data()

return updater

for arg_name, arg_type, _ in specification:
ui[f'{arg_name}-control'].subject.subscribe(update_argument(arg_name, arg_type))

controls.setFixedHeight(qt_info.inches_to_px(1.4))