Graphical User Interfaces (GUIs)

Dr Andy Evans

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Graphical User Interfaces (GUIs)

  • In general, Python isn't much used for user interfaces, but there's no reason for not doing so.
  • Build up WIMP (Windows; Icons; Menus; Pointers) Graphical User Interfaces (GUIs).
  • The default package to use is TkInter.
  • This is an interface to the basic POSIX language Tcl ("Tickle", the Tool Command Language) and its GUI library Tk.
  • Also more native-looking packages like wxPython: https://www.wxpython.org/

Basic GUI

import tkinter

root = tkinter.Tk() # Main window.

c = tkinter.Canvas(root, width=200, height=200)
c.pack() # Layout
c.create_rectangle(0, 0, 200, 200, fill="blue")

tkinter.mainloop() # Wait for interactions. 		GUI

Event Based Programming

  • Asynchronous programming, where you wait for user interactions.
  • In Python, based on callbacks: where you pass a function into another, with the expectation that at some point the function will be run.
  • You register or bind a function with/to an object on the GUI. When an event occurs, the object calls the function.

Simple Event

import tkinter
def run():
    pass

# Just showing menu elements
root = tkinter.Tk()
menu_bar = tkinter.Menu(root)
root.config(menu=menu_bar)
model_menu = tkinter.Menu(menu_bar)
menu_bar.add_cascade(label="Model", menu=model_menu)
model_menu.add_command(label="Run model", command=run)

tkinter.mainloop() # Wait for interactions. 		GUI

The user experience

  • Many people design for geeks.
  • Users learn by trying stuff - they rarely read manuals, so think carefully about what the default behavior of any function should be.
  • We need to design for the general public, but make advanced functions available for those that want them.
  • We should try to help the user by...
    • Using familiar keys and menus (e.g. Ctrl + C for copy).
    • Including help systems and tutorials.

Designing for users

  • At every stage when designing the GUI, think "is it obvious what this does?"
  • Make all screens as simple as possible.
  • Turn off functionality until needed, e.g.:
    model_menu.entryconfig("Run model", state="disabled")
    # Until the user has chosen files, then:
    model_menu.entryconfig("Run model", state="normal")
  • Hide complex functionality and the options to change defaults in 'Options' menus.
  • Most of all consult and test. There is a formal element of software development called 'usability testing' in which companies watch people trying to achieve tasks with their software.