Modified IDLE

23 Sep, 2018

Dean B writes:

I'm on page 137 of your book Python For Kids (chapter 10). I noticed a sentence at the top of the page, and have a question on it. It says "This won't work if you're using the modified version of IDLE that we set up in Chapter 1." I didn't remember seeing anything in chapter 1 on a modified version of IDLE. I looked back through chapter 1, but still don't see anything on the matter.

Would you please tell me what page that is on? I'm more curious than anything. I was frustrated with the "New File" window so I did a search and found IDLEX extensions and installed that. It works quite well for me. I would like to know though how your modified version works.

I'm new to programming and after searching for a good programming language to start with I chose Python, and after looking through a lot of books I chose your book "Python For Kids". I’m a senior citizen and have found this book to be a great introduction to Python. Certainly not just for kids as long as the adults are okay with the kid like context. Works for me, and thanks for such a good book.

Apologies for the confusion there -- this was a miss when we updated the book for later versions of Python 3. When Python for Kids was released in 2013 (end of 2012), you needed to make a minor modification to the shortcut used for starting up IDLE, to turn off "subprocess mode". Without going into too much detail about what that is, effectively if you ran IDLE with subprocess mode on, some of the graphical examples (tkinter, etc) would cause the Shell to hang. This was fixed in a later version of the IDLE runtime, and I removed those instructions from the first chapter on installation -- but completely missed the reference on page 137. Thanks very much for letting me know and I've updated the errata here.


Pygame or App Development using Kivy or XCode?

19 May, 2018

Sunil writes:

I would, first of all, like to thank you for the amazing book you have written "Python for Kids"
It's really helped my nephew learn Coding in a very exciting and fun way.
He is now very keen on continuing with Python. He is 8.
But at this point, I do not know what would be the next set of things to teach him. Should we proceed with learning Pygame or App Development using Kivy or XCode. I am a little confused on this matter.
I tried a bit of reading online, but it did not help my decision making.

What would you suggest is the best Python learning path for an 8-year-old after having followed your book.

I'm quite partial to the idea of Pygame as a natural progression from the games in the book. Adapting the Bounce or Stickman game to use Pygame, instead of tkinter, seems like a good way to get started, and then Pygame has support for audio (mixer) and joystick modules, so there's opportunities to enhance and extend the games to add new features. This would be building on learning from the book, which I think is a nice way to move forward. It's certainly going to be the easiest way to get some instant feedback as well (since it's not hard to get up-and-running), so thumb's up from that perspective.

I don't know a lot about Kivy - so I can't really comment on how suitable it would be for an 8 year old -- but even if it proved too difficult, if he's interested in mobile apps, then I don't think that time would be wasted.

XCode will probably mean learning a new language (depending on what your nephew wants to do with it). If iOS apps, then the options are Objective-C or Swift -- which is not to say you're entirely limited to those languages, but you're going to find the most community support with one of the primary languages. Of the two, Swift is the most approachable (IMO), but I still wouldn't call that easy going for a child to pick up.

So with very limited experience in the other two options, I guess my personal preference would be Pygame, then Kivy, finally XCode. Do let me know how you get on...

Reference links for other readers:


A question about tkinter update

09 May, 2018

Feng writes:

I bought a chinese version of your book. when i tried the paddle ball at this step: 'Bounce (example 4) - ball moving up and down' at the first part of the code, you add a line tk.update(). I cannot see why this is necessary, since there are no balls moving at all. Then, i comment it with a '#'.

Now, it comes with a problem, i failed to see the ball move down, it seems stuck at the top line of the canvas. I tried to print the variable 'pos', and it shows as follows:
------------------(some part of the outcome)
[255.0, 1.0, 270.0, 16.0]
[255.0, 0.0, 270.0, 15.0]
[255.0, -1.0, 270.0, 14.0]
how did this happen, why the first 'tk.update()' cannot be omitted?

The first call to tk.update() isn't strictly necessary - but what it does do is to force a "wait" until all the Tk user interface events have been processed.

When you call pack to tell your Tk components to resize and display themselves in the right place, you're actually sending a message to a whole separate process (this is the Tk event loop). Let's imagine it took 1 minute for each component to set itself up, and you had 10 components in the window. If you called pack it wouldn't take 10 minutes to complete that function call -- it would actually complete almost instantly. Behind the scenes however, the components are busy re-arranging themselves to fit in the window (and in this imaginary scenario, that process would then take 10 minutes to complete).

Try running this code (create a file and run it in IDLE):

from tkinter import *
tk = Tk()
canvas = Canvas(tk, width=500, height=400, bd=0, highlightthickness=0)
canvas.pack()
print(canvas.winfo_height())

You'll get 1. That's because the canvas hasn't finished rearranging itself by the time you call winfo_height. Now try typing the first 4 lines of the code into the IDLE shell -- wait a few seconds then enter the last line:

print(canvas.winfo_height())

Now you'll get 400 (i.e. 400 pixels high). Because you've given the canvas time to complete.

In summary, pack is saying "ok Tk components, re-arrange yourselves on the screen" and update is saying: "ok Tk, I want to wait for that to complete". Which is why, if you remove the update call, inside the __init__ function of the Ball class, it calculates a height of 1, and the code no longer works correctly.


Just in time?

01 Apr, 2018

Perhaps just in time for Google shutting down its goo.gl url shortener, here's a potential alternative: nimwhistle, an algorithmic URL shortener loosely based on the ideas in Whistle, but with a few minor modifications (URL patterns in the form of dir/YYYY/mm/dd/filename; 'favourite', fixed or non-standard URLs stored in a fixed-line-length file), and a CGI-based redirection service. 462KB compiled, Apache2 licensed. Not guaranteed for any purpose, because it was a hack-job/experiment, put together in a few hours.

Update: somewhat stupidly, forgot to mention, nimwhistle is already in use here (for example, https://jasonrbriggs.com/u/f1 redirects to Python for Kids)


Restarting the Bounce game (revisited)

04 Mar, 2018

Robin T writes (excerpted):

I am currently at chapter 14, i already made my first game called "Bounce". When the game is over, i want the user to push a button or a mouse click to restart the game. But i don't know how to do this.

Someone else asked a similar question a few years ago, so here's my post from back then, with some ideas about adding a restart button: "Restarting the game". In terms of creating a function to restart the game, you might want to use the canvas coords function to move the ball and paddle back to their starting position, and then set the values of all the other variables to the same as they started as well (for example, setting the hit_bottom variable to False; if you've added a score, setting the score back to zero; and so on). coords takes 5 parameters: the id of the object to move, the x and y position and the width and height of the object. So moving both objects back to their starting position might look something like this:

self.canvas.coords(self.paddle.id, 200, 300, 300, 310)
self.canvas.coords(self.ball.id, 245, 100, 260, 115)

Hopefully that helps.