Python has a few options for creating GUIs (Graphical User Interfaces). We will learn Tkinter because it is part of the standard library and easy to use.
GUIs are a type of user interface that allows users to run your program using viusal indicators like buttons, text boxes, and scroll bars. If you are creating a program that will be run by a casual user, a GUI is a good option.
Tkinter provides a python interface to the Tk GUI toolkit. Tk is a cross platform library that allows creating of native desktop GUI elements.
Tkinter is a module, so to start, we will have to import it
import Tkinter
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import tkinter
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root = Tkinter.Tk()
That didn't do much, did it. To actually create the window you have to run the mainloop function on your main window
root.mainloop()
This creates the window and starts listening for actions that the user takes. This is an infinite loop, and is one of the cases where an infinite loop is actually useful (don't worry, clicking the close button on the window will break out for the loop).
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root.mainloop()
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root.destroy()
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So far our GUI has been pretty boring. To make it useful we have to add "widgets" to it. Widgets are things like buttons, textboxes, labels, etc. Anything you would expect to have in a desktop application.
You need to create the widget after creating the main window, but before running mainloop
You will also need to let Tkinter know how to layout your widgets. Right now we will just use the pack method with no arguments.
widget.pack()You can create a button that when pressed will run a function. To do that you run the Button function. It takes the parent window as the first parameter, and then a list of key value params as options for look and feel, text, and command - the function that will run when the button is pushed. It returns a reference to the widget.
my_button = Tkinter.Button(window, text='my text', callback=myfunction)
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# A basic button
root = Tkinter.Tk()
# Widgets go here
w = Tkinter.Button(root, text='Hello')
w.pack()
# Run the gui
root.mainloop()
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# a button with a callback
def my_callback():
print("Here i am")
root = Tkinter.Tk()
# Widgets go here
w = Tkinter.Button(root, text='Hello', command=my_callback)
w.pack()
# Run the gui
root.mainloop()
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# A basic label
root = Tkinter.Tk()
# Widgets go here
w = Tkinter.Label(root, text='Hello')
w.pack()
# Run the gui
root.mainloop()
If you want to be able to update the text in a label, you will need to use a StringVar for the text, and instead of using text keyword param, you will use textvaribale keyword parameter.
var = Tkinter.StringVar()
l = Label(root, texvariable=var)
l.pack()
var.set('New text')
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# A changeable label
root = Tkinter.Tk()
# Widgets go here
v = Tkinter.StringVar()
w = Tkinter.Label(root, textvariable=v)
w.pack()
v.set('Aaaah')
# Run the gui
root.mainloop()
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# A basic entry
root = Tkinter.Tk()
e = Tkinter.Entry(root)
e.pack()
root.mainloop()
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# An entry where we get the text entered.
def what_entered():
print(e.get())
root = Tkinter.Tk()
e = Tkinter.Entry(root)
e.pack()
# Click to button to see what teh text entered is
b = Tkinter.Button(root, text='Say What?', command=what_entered)
b.pack()
root.mainloop()
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There are many other types of widgets including canvas for drawing images and shapes, menubutton for creating menus, radio and lists for making selection, and lots of other. Look to the documentation for more info: https://docs.python.org/2/library/tkinter.html
GUI programming uses a different model of programming than we are used to. In the past our program has run from top to bottom and the only way to change the outputs was to change the inputs (or use random...)
In GUIs we use event driven programming where we create our application and then listen for events like a user clicking a button or entering some data. When an event is created, then the callback function associated with that event runs. Then the next event causes a callback to run. This all happens in an infinite loop (mainloop) which is broken by you either calling destroy or close in your code in response to an event or by clicking the close button for the window.
In Event driven programming, the user determines the workflow. It will take some time to get used to thinking in these terms.
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# A basic button
root = Tkinter.Tk()
# Widgets go here
w = Tkinter.Button(root, text='Hello', width=50, height=1)
w.pack()
# Run the gui
root.mainloop()
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# A basic button
root = Tkinter.Tk()
# Widgets go here
w = Tkinter.Button(root, text='Hello', fg="red", bg="#00aaff")
w.pack()
# Run the gui
root.mainloop()
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# A basic button
root = Tkinter.Tk()
# Widgets go here
w = Tkinter.Button(root, text='Hello')
w.pack(side=Tkinter.LEFT)
# Run the gui
root.mainloop()
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# A basic button
root = Tkinter.Tk()
# Widgets go here
for i in range(3):
for j in range(4):
text = "{}-{}".format(i, j)
w = Tkinter.Button(root, text=text)
w.grid(row = i, column = j)
# Run the gui
root.mainloop()
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You will create a gui that calculates BMI. The formula is
(weight/ height^2) x 703
with weight in pounds and height in inches.
heightweightbmi
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