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The author describes the second line of code in Listing 7 as follows:

"The second line tells Tk to put the focus on our entry widget. That way the cursor will start in that field, so the user doesn't have to click in it before starting to type."

And finally , the author describes the third line of code in Listing 7 as follows:

"The third line tells Tk that if the user presses the Return key (Enter on Windows) anywhere within the root window, that it should call our calculate routine, the same as if the user pressed the Calculate button."

Now back to the calculate function

The calculate function, which is shown in Listing 8 , is executed whenever the user presses the calculate button or hits the Enter key on the keyboard as described above .

Listing 8 . The calculate function.
def calculate(*args): try:value = float(feet.get()) meters.set((0.3048 * value * 10000.0 + 0.5)/10000.0)except ValueError: pass

The input value in feet

Any value that is entered into the Entry widget is stored in the StringVar object referred to by feet as shown in Listing 3 and Listing 4 and as described above .

The StringVar object has a method named get that returns the string stored in the object. The code in the try block of Listing 8 calls the get method on the StringVar object and attempts to convert the string to type float .

Either save the float or pass

If the string cannot be converted to a float , a ValueError is thrown and control is passed to the pass statement. This causes the function to exit without doing anything.

If the string can be converted to a float , that float value is stored in the variable named value .

Calculate and display the result in meters

A StringVar object also has a method named set that can be used to store a value in the object. The code in the try block performs the arithmetic to convert the value in feet to a value in meters and then calls the set method on meters to store that value in the StringVar object referred to by meters in Listing 3 .

Storing a value in that StringVar object causes the value to appear in the Label immediately to the left of the word meters in Figure 2 due to the textvariable argument in Listing 5 . Once again, if you connect a widget to a StringVar object using a textvariable argument, a change in the contents of either will cause a corresponding change in the other.

Make everything run

Finally, the last statement in the program, which is shown in Listing 9 , causes Tk to enter its event-handling loop and causes everything to run. The code in this loop will monitor for an event indicating that the user has pressed the calculate button. When that happens, the calculate function will be executed causing the conversion from feet to meters to take place and causing the resultsof the calculation to be displayed as shown in Figure 2 . This is an infinite loop that will continue to run and monitor for events untilthe program is terminated.

Run the program

I encourage you to copy the code from Listing 9 . Execute the code and confirm that you get results similar to those shown in Figure 2 or Figure 4 . Experiment with the code, making changes, and observing the results of your changes. Make certain that youcan explain why your changes behave as they do.

Complete program listing

A complete listing of the program is shown in Listing 9 .

Listing 9 . Complete program listing.
# Illustrates a Python GUI using tkinter. # Published by Mark Roseman at TkDocs under a Creative Commons # Attribution-NonCommercial-ShareAlike 2.5 Canada (CC BY-NC-SA 2.5 CA) license.#------------------------------------------------------------------------------ from tkinter import *from tkinter import ttk def calculate(*args):try: value = float(feet.get())meters.set((0.3048 * value * 10000.0 + 0.5)/10000.0) except ValueError:passroot = Tk() root.title("Feet to Meters")mainframe = ttk.Frame(root, padding="3 3 12 12") mainframe.grid(column=0, row=0, sticky=(N, W, E, S))mainframe.columnconfigure(0, weight=1) mainframe.rowconfigure(0, weight=1)feet = StringVar() meters = StringVar()feet_entry = ttk.Entry(mainframe, width=7, textvariable=feet) feet_entry.grid(column=2, row=1, sticky=(W, E))ttk.Label(mainframe, textvariable=meters).grid(column=2, row=2, sticky=(W, E)) ttk.Button(mainframe,text="Calculate", command=calculate).grid(column=3, row=3, sticky=W) ttk.Label(mainframe, text="feet").grid(column=3, row=1, sticky=W)ttk.Label(mainframe, text="is equivalent to").grid(column=1, row=2, sticky=E) ttk.Label(mainframe, text="meters").grid(column=3, row=2, sticky=W)for child in mainframe.winfo_children(): child.grid_configure(padx=5, pady=5) feet_entry.focus()root.bind('<Return>', calculate) root.mainloop()


This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Itse1359-1610-GUI Programming
  • File: Itse1359-1610.htm
  • Published: 10/28/14
  • Revised: 01/31/16

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.

Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.


Questions & Answers

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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